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Relation of RA to Relative Fitness

In their detailed review of reproductive allocation in plants, Bazzaz and Ackerly (1992) maintained that if two plants of equal size differ in their allocation to reproduction, the individual with the higher allocation would be expected to have higher reproductive success in terms of contribution to future regeneration of the population. If RA is to be meaningful to the evolutionary ecology of plant populations, it should be clearly associated with fitness (Reekie, 1999). Unfortunately, definitions of fitness may be difficult to develop, especially in clonal species where traditional measures based on sexually produced seeds or fruits are inappropriate (Pedersen and Tuomi, 1995 Wikberg, 1995 Winkler and Fischer, 1999). For the annual Triplasis purpurea, a measure of relative fitness based on seed output is reasonable, since the recruitment of new individuals is only possible from a seed. Cheplick and Wickstrom (1999) performed a competition experiment designed to investigate the...

Multidimensional space of realized fitness

Multidimensional Space

Potential fitness of potential fitness of Fig. 3.4 Model of costs and benefits of induced defense in the multi-dimensional space of environmental conditions. Within this space, each plant genotype has a limited opportunity to realize a certain fitness level. The realized fitness of a genotype with increased resistance to one or more environmental stresses can be restricted under a variety of conditions. Fitness of genotype II (light gray) with increased anti-herbivores defense is lower than that of the less-defended genotype I (dark gray) in environments with high levels of competition, drought, or attack by pathogen C (right dotted line). However, in environments with high levels of herbivore attack (left dotted line), the realized fitness of genotype II is greater than that of genotype I. In intermediate stress environments (in the center of the overlapping areas), the two genotypes have similar realized fitness levels The empirical evidence for costs of induced defense remains...

Concepts And Definitions

The resistance concept has its roots in plant breeding research (e.g., Painter 1958 Maxwell and Jennings 1980). During recent years ecologists have elaborated on the breeding concepts but without consistency in terminology. This is not the place to thoroughly discuss the conceptual basis of resistance and related terms, but it is important to define a few key concepts. For the purpose of this chapter I follow, with some modifications, the definitions proposed by Karban and Baldwin (1997), and Strauss and Agrawal (1999). This view is different from the Painter (1958) definition in that it separates resistance from tolerance (see Fig. 1). Painter's definition focuses on damage to the plant any plant characters that minimize damage will contribute to resistance, be they toxins, deterrents or compensatory processes. Thus, he viewed compensation, or tolerance, as one component of resistance, and others after him have adopted this view (e.g., Berenbaum and Zangerl 1992a). Research during...

Empirical Patterns in Reproductive Allocation

RA is central to several questions in life history theory, as it is assumed that patterns of RA are directly related to fitness (Calow and Townsend, 1981). In the words of Stearns (1976) The key life-history traits are brood size, size of young, the age distribution of reproductive effort, the interaction of reproductive effort with adult mortality, and the variation in these traits among an individual's progeny.

Evolutionary significance of bryophytes

Evolution is the result of a suite of incessant attempts to improve fitness and take advantage of opportunities, such as escaping competition and occupying a new habitat. Pilgrims, fleeing the biotic interactions in the aquatic habitat, faced severe abiotic selection forces on land. How many attempts were made to conquer land is not known, but at least one of them led to the successful establishment of a colony. At least one population of one species had acquired a suite of traits that allowed it to complete its life cycle and persist on land. The ancestor to land plants was born. It may have taken another 100 million years for plants to overcome major hurdles, but by the Devonian Period (approximately 400 mya), a diversity of plants adapted to the terrestrial environment and able to absorb water and nutrients, and transport and distribute them throughout their aerial shoots, occupied at least some portions of the land masses. Soon thereafter, plants were freed from the necessity of...

Resistance In The Context Of Complex Interactions

In natural systems, plant resistance is one of many selective agents affecting herbivore fitness. It is particularly important to recognize that effects of plant resistance traits on insect growth and survival can be much modified by natural enemies, i.e., tri-trophic level effects (Price et al. 1980 Agrawal 2000b). In certain interactions the insect has not only evolved mechanisms to cope with plant secondary metabolites but has taken advantage of their toxic properties for use in defense against its enemies (Rowell-Rahier and Pasteels 1992). This type of defense probably offers a considerable fitness gain, and thus could have been an important factor in the evolution of host plant specialization in herbivorous insects (Bernays and Graham 1988). For example, larvae of the leaf beetle Phratora viteiiinae suffer higher mortality from generalist predators when forced to feed on willow leaves lacking salicin, the precursor of its anti-predator defense, than larvae fed leaves of its...

Resistance And Insect Population Dynamics

Time scale is an essential component for assessments of the importance of plant resistance to insects. When testing hypotheses on an evolutionary time scale, it may be appropriate to ask, for example, whether or not differences in resistance among plant genotypes lead to statistically significant variation in insect fitness. If so, then there is potential for plant traits to influence the evolution of insect life history traits. However, when examining processes on an ecological time scale, the magnitude of the effect, not only statistical significance, needs to be taken into account (Fowler and Lawton 1985 Kyto et al. 1996). For example, whether or not variation in a particular resistance trait can account for ups or downs in insect numbers needs to be examined in the context of other factors influencing the performance of the insect, in particular, density dependent factors that may overshadow any effects that plant traits have on the performance of insect individuals (Hunter 1997).

Further Adventures and Advances

Although the mechanism of quenching has largely been resolved, numerous questions about the xanthophyll cycle remain. The physiology of the cycle is not well understood. The pool size of violaxanthin and the fraction of the pool that is active in the cycle vary among plant species and growth conditions (Demmig-Adams et al., 1999, this volume). There is a growing body of evidence that the cycle's operations may be related to more than just NPQ (Yokthongwattana and Melis, this volume). If the cycle has multiple functions, how are these functions regulated Mutant studies suggest that the cycle in not essential for photosynthesis (Jung and Niyogi, this volume) and yet, as far as I am aware, all wild-type plants have the xanthophyll cycle. Why has nature retained this complex, apparently multifunctional system if it is not of some critical advantage Did the system provide the adaptability to light environments needed for terrestrialization over multiple generations Is it simply...

Life histories reproductive strategies and allocation

The strategy of producing both vegetative offspring and seeds may maximize fitness by combining the advantages of both forms of reproduction. Asexually reproducing animals such as water fleas and aphids usually have a sexual phase in their life cycle, often after a number of asexual generations. Green & Noakes (1995) provide a model demonstrating that even a small component of sexual reproduction can be highly advantageous in an otherwise clonal life cycle. Plants can often switch between the two modes of reproduction in a phenotypic response to changing conditions, especially to increased density (Abrahamson, 1975 Douglas, 1981). Many species that form large clones have mechanisms for avoiding inbreeding. Nettles (Urtica dioica), dog's mercury (Mercurialis perennis), creeping thistle (Cirsium arvense) and butterbur (Petasites hybridus) all have clones that are either male or female (that is, the species are dioecious). This separation of the sexes ensures that only outbreeding...

Diversifying Selection Results from Direct RAvr Recognition

If an R protein detects an Avr protein by direct interaction and triggers host resistance, selection pressure should be imposed on the pathogen carrying the Avr gene to evade recognition. This could be achieved by structural changes in the Avr protein through mutations without necessarily affecting its virulence function. In this case, the Avr recognition by the R gene may be unrelated to its virulence function, so mutations that abolish recognition may retain function with little or no fitness penalty to the pathogen (Dodds et al. 2006). Once the host resistance is overcome, the selection pressure would be on the plant to generate a new R gene to recognize the mutated Avr. This R-Avr coevolutionary arms-race may have two outcomes. One is that single R (Avr) alleles of the corresponding genes sweep through the host (pathogen) populations, due to directional selection for advantageous alleles (Bergelson et al. 2001). However, this situation has rarely been documented in natural plant...

Direct Defenses in Plants and Their Induction by Wounding and Insect Herbivores

Resistance factors for direct plant defense against herbivorous insects comprise plant traits that negatively affect insect preference (host plant selection, oviposition, feeding behavior) or performance (growth rate, development, reproductive success) resulting in increased plant fitness in a hostile environment. Such traits include morphological features for physical defense, like thorns, spines, and trichomes, epicu-ticular wax films and wax crystals, tissue toughness, as well as secretory structures and conduits for latices or resins. They also include compounds for chemical defense, like secondary metabolites, digestibility reducing proteins, and antinutritive enzymes. All these traits may be expressed constitutively as preformed resistance factors, or they may be inducible and deployed only after attack by insect herbivores. The induction of defensive traits is not restricted to the site of attack but extends to non-infested healthy parts of the plants. The systemic nature of...

General Model for Evolution of the Plant R Gene System

Fig. 1 A general model for plant-pathogen coevolution. Plants possess a multilayered defense system to ward off potential pathogens. MAMP-triggered immunity (MTI) constituted an important part of non-host resistance (Phase I). The pathogen delivered effector proteins a and b into the host cell to suppress the MTI and eventually overcame non-host resistance (Phase II). In response to the pathogen-imposed pressure, the plant evolved specific R proteins 1 and 2 to recognize the effector protein (referred to as Avr factors) a directly in a receptor-ligand interactive manner and b indirectly by detecting its virulence activity, respectively, thereby inducing a stronger defense response (Phase III). In response to the plant-imposed pressure, the pathogen accumulated mutations that change the structure of effector a to escape recognition by R protein 1 , resulting in suppression of R-resistance. In the other scenario, effector gene b might have been deleted in the pathogen population if this...

Inducible Resistance Factors for Direct Defense

Since the initial observation of proteinase inhibitor accumulation in wounded tomato and potato plants, inducibility by herbivory has been shown for a large number of other potential resistance factors (Walling 2000 Gatehouse 2002). In the light of recent studies analyzing induced responses at the level of the entire transcriptome, we now begin to appreciate the full breadth and highly dynamic nature of plant-insect interactions. Numerous studies have shown that herbivory causes large-scale changes in gene expression (Cheong et al. 2002 Delessert et al. 2004 Reymond et al. 2004 Smith et al. 2004 Voelckel and Baldwin 2004 Zhu-Salzman et al. 2004 De Vos et al. 2005 Schmidt et al. 2005 Ralph et al. 2006b Thompson and Goggin 2006 Broekgaarden et al. 2007). In hybrid poplar, for example, it is estimated that 11 of the transcriptome is differentially regulated by insect feeding (Ralph et al. 2006a). However, inducibility of a certain gene or enzyme per se is not sufficient evidence for a...

Photoacclimation Yin Yang and the Compromise between Photoinactivation and Photoprotection

Thus the ecotypes of Solanum dulcamera ( bittersweet ) discovered by Gauhl (1976) were used to uncover the limiting role of nitrogen nutrition in shade-sun acclimation with increased sensitivity to photoinhibition under low nitrogen (Ferrar and Osmond, 1986). Nitrogen dependence was also established for photoacclimation and survival of intertidal Ulva ro-tundata in seawater (Henley et al., 1991) and the possibility emerged that a nitrogen-depleting biotic stress, such as severe virus infection, could also influence photoacclimation (Balachandran and Osmond, 1994) and the fitness of infected plants in shaded and sun habits (Funayama et al., 2001). In general, limiting nitrogen prevents acclimation, i.e. increase in light-saturated photosynthesis, presumably because of the huge nitrogen investment in Rubisco, and renders plants more sensitive to photoinhibition. Indeed, Kato et al. (2003) have now shown that the first order rate constant for PS II photoinactivation is determined by the...

The everchanging weed spectrum

Climate change is predicted to have significant effects on both the geographical distribution of weeds and on the severity of weed infestations. Evolutionary rate (for instance, in the development of herbicide resistance) has been demonstrated to vary dependent upon both temperature and moisture availability. This is probably a result of a combination of factors including generation time, population size and relative fitness of herbicide-resistant individuals. All of these factors may be affected by increased average global temperatures and subsequent differences in regional weather patterns (Anon., 2000). In addition, milder winters and warmer summers may allow for survival and population growth of species that were previously unsuited to a region's climate. Increases in the occurrence of Phalaris grasses in the UK in recent years may be a direct result of this (A.H. Cobb and J.P.H. Reade, personal observations).

Coevolution of Plants and Their Pathogens

Co-evolution includes population-level processes of reciprocal adaptation of interacting species. Reciprocal traits involved in co-evolution include pathogen infectivity and host resistance. As host defences may reduce the fitness of parasite, host and parasites may co-evolve, defining co-evolution as the process of reciprocally adaptive genetic change in two or more species. Accordingly three conditions that should meet for host pathogen co-evolution are (1) genetic variation in the relevant host and pathogen traits (2) reciprocal effects of the relevant traits of the interaction on the fitness of host and pathogen (3) dependence of the outcome of the host-pathogen interaction on the combination of host and pathogen genotypes involved 34 . For plant-virus co-evolution taking Arabidopsis thaliana as model system, there are only partial evidences regarding the detrimental effects of highly virulent viruses in crop production. In such cases, the infection is not necessarily linked to a...

How to Detect Approaching Allogeneic Cells as Foreign and to Eliminate Them Allorecognition and Cell Lineage

These allorecognition responses play a fundamental role in maintaining the genetic and physiological integrity of the colony (Yund et al. 1987 Buss and Yund 1988 Yund and Parker 1989) because the germ line is not sequestered and because interstitial cells migrate within Hydractinia colonies. Thus, since allogeneic colonies which have the appropriate haplotype will fuse despite the fact that the rest of their genomes are different, in permanent fusions there is competition at the level of cell lineages. This may be as significant as selective death in rejections since, depending on the outcome of allorecognition reactions, the original members of the chimera risk losing access to the germ line, and thus risk reduced fitness, through somatic cell parasitism (Buss 1982 Buss and Shenk 1990).

Metabolic Reconfiguration to Shift from a Growthto a Defense Oriented State

Efficient mobilization of plant resources is likely to facilitate the expression of costly resistance traits, including the accumulation of defense proteins, the synthesis of secondary metabolites, and the formation of structural defenses. On the other hand, mobilization of resources may also contribute to plant tolerance of herbivory. Unlike resistance, tolerance does not affect herbivore preference or performance, but rather allows the host plant to minimize the fitness consequences of tissue loss. Tolerance and resistance are therefore viewed as alternative and complementary strategies for plant defense against insect herbivores (Karban and Myers 1989 Mauricio 2000 Weis and Franks 2006). Whereas tolerance is still not well-understood at the molecular level, it may include the mobilization of leaf carbon and nitrogen that is threatened by herbivory, and temporary storage of these resources for later re-growth. The induction of protein turnover, lipid and carbohydrate metabolism, and...

Plants exhibit mitotic senescence postmitotic senescence and cell quiescence

Cell quiescence also occurs in plants. Cells of apical meristems will stop dividing under unfavorable conditions. For example, the apical meristems of many trees will stop proliferative process when they perceive the short-day photoperiod signal short day often means that the winter season is coming. These meristem cells retain their division capability during winters and will resume division activity when spring is coming. Therefore, the short-day-induced cell quiescence is an evolutionary fitness strategy. A recent study shows that ethylene and abscisic acid may play a role in regulating the temporary 'arrest' of tree meristem (Ruonala et al., 2006).

The Assumptions of the Models

The first model (Eqs (2.1)-(2.4)) and the model of Huber and During (2001) predicted that there often is an intermediate optimum of allocation to reproductive meristems. The models assumed that reproductive allocation is constant over time. The second model, Eqs (2.5)-(2.7), showed that bang-bang reproduction has the highest fitness. Optimal control models of the resource budgets of annual plants often predict a similar allocation pattern as the latter model (Cohen, 1971 Perrin and Sibly, 1993). The great majority of plant species, however, do not follow either of the strategies reproductive allocation is not concentrated in the end of the life span, although it is plastic.

The Function of Dormant Buds

Dormant buds may well be an indication of resource limitation, but other possibilities also exist. Dormant buds may form a reserve that is mobilized if active shoots are lost. Several bud bank models have been presented to explain compensatory responses of plants to herbivores (van der Meijden, 1990 Vail, 1992 Tuomi et al., 1994). The starting point has been to explain controversial observations of overcompensatory responses, according to which plants may have higher fitness when damaged than when they are left intact (Paige and Whitham, 1987 Lennartsson et al., 1997). The general idea of the bud bank models is that when herbivory pressure is high and predictable, it is beneficial to produce dormant buds in locations protected from herbivores. Additional conditions for the evolution of overcompensation are that activation of dormant buds is not possible without a signal from damage and that probability of repeated damage is low (Nilsson et al., 1996 Lehtila, 2000). More generally,...

Nematode Microbial Associations Diversity Enemies of Their

Biofilm-like structure that resembles the one formed by Yersinia sp (Couillault and Ewbank 2002). A natural endosymbiont of C. elegans has yet to be found. The second example relates to virus associations. The vector relationship between plant-parasitic nematodes and plant viruses has been long known. Nematode vectors demonstrate great efficiency and specificity in those viruses they transmit of the several hundred PPN species no more than few species in the genera Xiphinema, Longidorus, Trichodorus and Paratrychodorus are able to transmit viruses. Virus particles are retained on the cuticular lining of the oesophagus and can be maintained after extended periods of starvation. During molting, and as they shed their cuticles, juveniles also lose their ability to transmit viruses. It has been generally assumed that nematodes are only passive virus vectors. This is because virions do not replicate within their hosts and do not seem to affect nematode reproduction (Das and Raski 1969)....

PsbS and its Relatives

From the discussion of sustained NPQ in photoinhibited evergreens in the previous section, the question arises as to whether or not ApH-independent NPQ is facilitated by PsbS. PsbS facilitates ApH-dependent NPQ (Li et al., 2000, 2002b Jung and Niyogi, this volume) and increases plant fitness under moderate, intermittent levels of excess light (K lheim et al., 2002) as shown in the model for short-lived species, Arabidopsis. PsbS is protonated during the development of excess light, and is thus thought to act as the pH sensor that triggers ApH-dependent, flexible NPQ (Li et al., 2002b Jung and Niyogi, this volume). But does

Life History Strategy LHS of Gigasporaceae as Revealed Using Monoxenic Cultures

Life histories patterns are often related to variation in reproductive activity, or reproductive effort which measures the amount of available resources allocated to reproduction over time (Begon et al. 1996). However, reproductive effort is difficult to measure. One simple way to have an idea about reproductive effort is by calculating the Malthusian fitness (MF). The MF, in this case, compared the instantaneous change of spore production over time in relation to the starting inoculum (Fig. 2B). For a discussion about the application of MF to filamentous fungi, the reader can refer to Pringle and Taylor (2002). The evolution of the MF in S. reticulata was clearly different from that of the Glomus species (Fig. 2B). The same trend was observed in other species of these two families cultured under monoxenic culture conditions (Fig. 3). Gigasporaceae species studied in monoxenic culture have shown a short overlap of sporulation with the active growing phase of the roots, while Glomus...

The Functional Ecology of Water in the Life of a Flower

That flowers are costly to the water budget of the plant is supported by geographical patterns of sex allocation in relation to drought stress. The frequency of self-pollination coupled with reduced allocation to floral display and flower longevity correlates with habitat aridity (Guerrant, 1984 but see Jonas and Geber, 1999). In subdioecious species made up of male, female, or hermaphroditic sex morphs, unisexuality typically increases with habitat aridity (Barrett, 1992 Costich, 1995 Weller et al., 1995 Case and Barrett, 2001). This trend suggests that the water cost of simultaneous allocation to both male and female sexual functions imposes a fitness disadvantage for plants with hermaphroditic flowers that favors the maintenance of dioecy under drought (Webb, 1999). In subdioecious Wurmbea dioica, cosex-ual plants have reduced rates of leaf transpiration and higher water use efficiency compared to unisexual individuals, suggesting a history of selection for conservative water use...

The Impact Of Pathogens On Plant Interference And Allelopathy

Pathogenesis can have both detrimental and beneficial impacts on plant fitness. As such, pathogens are important forces that influence the structure and dynamics in natural and manipulated plant ecosystems. Plant production and numbers within a community are constrained by environmental limitations, which are often mediated through plant interference. Competition for resources and allelopathy (chemical interactions) are the two most important ways that plants interfere with each other. This chapter reviews the effects of pathogens on the competitiveness and allelopathic ability of their hosts. In most cases, pathogens reduce the competitive ability of their host, making the host prone to displacement by neighbouring, resistant plants. However, pathogens may simultaneously increase the allelopathic ability of their hosts, thereby offsetting their loss in competitiveness to varying degrees. Evidence for enhanced allelopathy by infected plants comes in two forms (i) pathogens...

Water Relations and the Evolution of Floral Traits

Under arid conditions, allocation of water to support floral display can be costly to future growth and survival. Nobel (1977) modeled costs associated with diversion of water from leaves to inflorescences of the desert succulent, Agave deserti. His analysis suggests that the water cost of flowering is sufficient to explain the death of the vegetative plant after a single bout of reproduction. The resource cost hypothesis (Galen, 1999) postulates that when allocation costs of flower production and maintenance have significant fitness consequences, they may select for reductions in floral display countering selection exerted by animal pollinators. Ashman and Schoen (1994) make a similar argument for the impact of flower maintenance costs on the evolution of floral longevity. While their hypothesis addresses the physiological costs associated with the amount of time spent in pollen transfer rather than pollinator attraction per se, water figures prominently in both trade-offs. Water use...

Basal Constitutive Response

DAF-16 is required in the intestine to extend the life-span of daf-2 mutants (Libina et al. 2003). Long-lived worms with mutations in daf-2 show increased resistance to many pathogens (Garsin et al. 2003 Troemel et al. 2006) and have also enhanced evasion behavior (Hasshoff et al. 2007). It is therefore possible that one of the roles of the DAF-16 immune effector targets is to contribute to longevity of the worm. Reflecting also the overlap in the mechanisms by which DAF-16 mediates pathogen resistance and responses to stress, Chavez et al. observed that genes required for oxidative stress under the control of DAF-16 (including the superoxidase dismutase sod-3, and the catalases ctl-1 and ctl-2) are also required for the enhanced pathogen resistance afforded by daf-2 mutants. The authors hypothesized that by overproducing oxidative stress enzymes, daf-2 mutants may increase their fitness towards controlling the damage occurring during the pathogen interaction (Chavez et al. 2007).

Flexible Energy Dissipation

For a high light-grown leaf, such increases in thermal energy dissipation and decreases in maximal PS II efficiency are flexible they are rapidly reversible upon transition to non-excessive light or darkness as the de-protonation of PsbS presumably leads to a rapid disengagement of Z + A from their thermal dissipating function and a return to high PS II efficiency in limiting light. Hence NPQ is designated as NPQflex in Fig. 1A. Upon such transitions, however, Z + A are converted much more slowly to V by zeaxanthin epoxidase, and under these conditions the linear correlation between the amount of Z + A and the level of thermal energy dissipation no longer exists. On the other hand, retention of Z + A under such conditions permits a more rapid engagement of energy dissipation upon a subsequent exposure to excessive light (Demmig-Adams et al., 1989b Barker et al., 2002), since it only requires the rapid protonation of PsbS without the (slower) enzymatic conversion of V to Z + A. This...

Low Nutritive Quality Of Douglasfir Foliage

Likewise, Douglas-fir trees resistant to budworm defoliation had higher levels of sugars in their foliage than susceptible trees at all three sites (Clancy, 2001). This is in agreement with results from artificial diet bioassays budworm fitness was best on artificial diets with sugar (i.e., sucrose) concentrations of 6 dry weight, which is near the lower limit observed for Douglas-fir foliage (Clancy, 1992b) (Fig. 3). Clancy et al. (1992) evaluated the effects of terpene compounds on budworm survival and reproduction by forming gelatin-walled microcapsules around eight terpenes that are common constituents of Douglas-fir oleoresin. The microencapsulated terpenes were mixed into artificial diets to determine the effects they had on budworm fitness, using the three generation bioassay technique developed by Clancy (1991b). Five monoterpenes tested (a-pinene, 3-pinene, camphene, myrcene, and limonene) had little or no detectable effect on budworm fitness, when they were tested at...

The multiple origins and mechanisms of syncarpy in the angiosperms

The major evolutionary advantage of syncarpy is probably to allow a regular repartition of pollen tubes within the gynoecium by the formation of a 'compitum', which consists of tissues that permit pollen tube transfer between carpels (Endress, 1982). Accordingly, a visit to a syncarpic by a single pollinator might result in full seed set. Another potentially important advantage of syncarpy results from the enhanced competition between pollen tubes that this phenomenon produces, which may act as a filter of fitness by selecting for vigorous male parents. Syncarpy also allows the production of larger fruits, with potentially more complex and efficient seed dispersal mechanisms (Walker, 1978 Endress, 1982 Armbruster et al., 2002). A further advantage of syncarpy may stem from its potentially lesser requirement for cell wall synthesis, compared to an apocarpic gynoecium of similar total size.

Genetic and Functional Analyses of Transporters in Pollen Development and Tube Growth

The expectation is that most of the 746 pollen-expressed transporters in Ara-bidopsis will eventually be found to contribute to the development or fitness of pollen. The following are examples of gene knockout approaches that combined with other results have begun to reveal insights into pollen transporter functions. Although gene knockouts provide powerful tools, additional insights are expected from experimental strategies that include silencing, overexpression, and the use of dominant negative transgenes (Twell et al., this volume Guermonprez et al., this volume).

Implications For Pathogen Aggressiveness And Evolution

(b) Under the above conditions, chance mutation favours the appearance of a novel resistance gene preventing pathogenesis through enhanced resistance. These resistant individuals have a greater fitness than their susceptible neighbours and, consequently, increase in frequency within the population. (d) As resistance is broken down, the advantage of the previously resistant host genotype in terms of plant fitness is lost, and its frequency within the population falls. The importance of virulence (the degree or measure of pathogenicity) in determining the ability of a pathogen to infect a particular host is central to the concept of co-evolution of plants and pathogens. Despite this, its importance has often been emphasised to the exclusion of another component of pathogen fitness - aggressiveness (Burdon, 1987). In plant pathology, the term aggressiveness has been defined inconsistently (Jarosz and Davelos, 1995 Kirchner and Roy, 2002) or considered synonymous with virulence (Parker...

Channels VIC Family

In SPIK AKT6 (At2g25600) showed decreased rate of tube growth in K+ ext ranging from 5 M to 1 mM, and reduced hyperpolarization activated K+ n current (Mouline et al. 2002). The channel properties suggest SPIK is active at the PM and that it mediates bulk transport involved in K+ nutrition. The spik-1 mutation did show a general decrease in pollen fitness, suggesting that SPIK mediates K+ uptake in growing pollen tube, and has a role in pollen tube development and pollen competitive ability. The residual K+-dependent germination in the spik-1 mutant is likely due to other K+ permeable channels. However, gene disruption of another pollen-specific K+ n channel, TPK4 (KCO4), did not appear to alter pollen tube growth (Becker et al. 2004), though the ratio of the instantaneous current to the steady state current was reduced in the mutant pollen tube. TPK4 may be related to the spontaneously activating K+ channel characterized in lily pollen (Dutta and Robinson 2004). Localized to the PM,...

Siderophore mediated competition for iron and rhizosphere competence

Pseudomonads are not alone in their ability to use heterologous siderophores, and it appears that the ability to use a variety of siderophore types can provide an advantage to rhizosphere microorganisms. Examples of the diversity of systems that can be carried by individual species of bacteria include E. coli where various strains have been isolated that have transport systems for enterobactin, ferrioxamine B, ferrichrome, and citrate or various combinations of the above. Another example is Bradyrhizobium japonicum which uses the hydroxamate-type siderophores ferrichrome and rhodotorulate, ferric citrate, and is also able to use pseudobactin (Plessner et al., 1993). The advantage of being able to cross feed on different siderophores is nonetheless difficult to demonstrate as a consistent one. For example, a strain of Pseudomonas spp. carrying the plasmid pCUP2 which codes for a membrane receptor that allows use of ferric pseudobactin M114 was shown to be cross fed by a variety of...

Environmental control of carbon dioxide exchange

A plant survives only where the annual environmental regime includes periods favourable for metabolism and growth and where, in the case of perennials, there are no periods of lethal stress. Most polar plants, vascular and non-vascular, are perennials, and must therefore show resistance to both elastic and plastic stress. Levitt (1980) defines a biological stress as 'any environmental factor capable of inducing a potentially injurious strain in living organisms' a plastic stress is one producing irreversible chemical or physical change, e.g. frost damage, while an elastic stress results in a reversible change such as a major reduction in net assimilation rate (NAR) under suboptimal conditions. This chapter begins to examine the features that enable bryophytes and lichens to survive under the apparently severe stress of Arctic and Antarctic environments. Such features include, first, general characteristics of these plants that confer fitness under polar conditions and, second,...

Allometry of Modules

Figure 4.4 Relation of relative fitness to RA (upper) and plant mass (lower) for Plantago asiatica. Mature plants at the fruiting stage were collected from habitats along an altitudinal gradient in Japan. Data are from Table 2 of Kawano and Matsuo (1983). See text and Table 4.1 for regression results. Figure 4.4 Relation of relative fitness to RA (upper) and plant mass (lower) for Plantago asiatica. Mature plants at the fruiting stage were collected from habitats along an altitudinal gradient in Japan. Data are from Table 2 of Kawano and Matsuo (1983). See text and Table 4.1 for regression results.

Determinants of Allometry

Indirect effects of other plant traits Investigations into the allometry of RA should also explore the many other interacting plant traits that typically impact vegetative mass. Not surprisingly, both morphological and physiological traits have been shown to influence vegetative mass and consequently, individual reproductive fitness (Farris and Lechowicz, 1990 Callahan and Waller, 2000 Gibson, 2002). For example, in the annual Triplasis purpurea,

Environmental Stress and Role of Arbuscular Mycorrhizal Symbiosis

Mycorrhizae are widespread symbioses between plant roots and soil fungi, involved in the absorption of nutrients from the soil. Arbuscular mycorrhizae (AMs) are made up of a wide range of land plants, including at least 80 angiosperms, and fungi belonging to the glomeromycota. They generally have a positive effect on plant growth and nutrition, and improve the absorption of relatively immobile nutrients, such as phosphate, particularly in low nutrient soils or under drought. Moreover, AMs have been shown to promote plant fitness under a variety of stress conditions. In this chapter, we provide an overview of the effects of AM colonization on host plants subjected to drought stress and soil pollution, two of the most common types of stress that limit plant growth, and of the possible mechanisms involved in the beneficial effects of AM fungi.

Additional Functions Of Floral Scents

The primary function of floral scent in flowering plants is to attract and guide pollinators.43-121-124 However, additional functions are ascribed to the presence of volatile chemicals in flowers (reviewed in Pichersky and Gershenzon125), including defense and protection against abiotic stresses. These additional functions may help explain some of the abundance and variety of different constituents detected. Because flowers produce pollen and ovules for the next generation, they have a high fitness value to the plant, and the finding of chemicals that defend flowers against herbivores and pathogens is not surprising. Apart from attracting pollinators, floral scent chemicals may also increase the risk of herbivore attack on floral structures, as shown in Nicotiana attenuata, and floral tissues may therefore require relatively more protection from enemies.87 In N. attenuata, this was achieved through a herbivore-induced increase in corolla pools of nicotine, a biocidal defense...

Responses of Community Members to Induced Indirect Plant Defense

Induced infochemicals (sensu Dicke and Sabelis 1988), once released from the plant, can be exploited by any of its community members, including neighboring plants, herbivores, predators, parasitoids, pollinators and other community members, both above- and belowground (Fig. 2.3). The infochemicals can function as a direct defense by repelling herbivores. For example, butterflies avoid oviposi-tion on plants that are induced by either the presence of eggs or feeding damage (Rothschild and Schoonhoven 1977 Landolt 1993 De Moraes et al. 2001). High levels of direct defense may deter herbivores from feeding or ovipositing on a plant, and may also slow down development of larvae, rendering them more vulnerable to natural enemies (Rothschild and Schoonhoven 1977 Stout and Duffey 1996 Thaler et al. 1996). However, direct and indirect defense mechanisms can act antagonistically. Plant toxins that are ingested by the herbivore may be sequestered to affect the development of carnivores, or...

Avenues for Mitigating the Cost of Reproduction

Some of the resources invested in reproduction are recoverable and this may partially mitigate proximate costs. Any structure that remains attached to the parent plant, rather than being abscised or dispersed at maturity, contains potentially reclaimable nutrients. For example, reabsorption of unremoved nectar occurs in some plant species (e.g., Burquez and Corbet, 1991), and there is evidence that reabsorption of these energy-rich sugars increases fruit quality and seed fitness in an epiphytic orchid (Luyt and Johnson, 2002). A study in Sidalcea oregana revealed that in contrast to plant parts shed at maturity (pollen and seeds), 50-80 of nitrogen and phosphorus is reabsorbed from floral structures that remain attached to the plant (calyces, petals, unfertilized ovules Ashman, 1994b). There is also potential for the reabsorption of resources from early aborted fruits, although there is little evidence to address it (Obeso, 2002). In contrast to unfertilized ovules, plants are not...

Responses of Members of the Third Trophic Level

Plants can benefit in terms of fitness gain from carnivores that attack the herbivores (Van Loon et al. 2000 Fritzsche-Hoballah and Turlings 2001). Herbivores, however, are under selection to be inconspicuous, and are small in comparison to the plants they are feeding on. Consequently, carnivorous arthropods often depend on plant cues to locate their herbivorous victims (Turlings et al. 1990 Steinberg et al. 1992 Vet and Dicke 1992 Geervliet et al. 1994). Even though host-derived

Facultative Hemiparasite to Obligate Hemiparasite Increased Host Specificity

Hosts that may reduce, rather than increase, relative fitness. Factors directly influencing this balance include the level of fluctuation in yearly host populations, combined with the level of genetic variation for both autotrophic and heterotrophic abilities maintained in parasite populations.

Potential Causes of Sexspecific Physiology

This hypothesis has several prerequisites - foremost, evidence of genetic variation and heritability of physiological traits (Geber and Dawson, 1997 Arntz and Delph, 2001 Arntz et al, 2002). Given evolutionary potential, this hypothesis assumes that sexual dimorphism in physiology follows, rather than precedes, the separation of the sexes. Phylogenetic studies or sister comparisons of groups differing in sexual system may help elucidate the order in which sexually dimorphic traits evolved (e.g., Miller and Venable, 2003). Artificial selection experiments may also reveal the potential for divergence once separate sexes are established (e.g., Delph et al, 2004). If sex morphs can be artificially selected to vary in a physiological trait of interest, e.g., photosynthetic rate or water use efficiency, one could relate this variation to an estimate of fitness for each sex. The creation of broad intramorph variation in physiology via artificial selection that is not entirely explained by...

Ectomycorrhizal Associations and Their Significance for Phytoremediation

Mycorrhizal fungi play a key role in nutrient cycling and ecosystem functioning and have a profound effect on the composition of plant and microbial communities and thereby also on the capability of these communities to degrade anthropogenic pollutants. ECM fungi enhance the uptake of phosphate (P) and nitrogen (N), and can also contribute to the supply of the host with trace elements, such as copper (Cu) and zinc (Zn) (Smith and Read 2008). Furthermore, mycorrhizal plants have a higher resistance against abiotic (e.g., drought, heavy metals) and biotic (plant pathogens) stresses (Smith and Read 2008). In return, for these beneficial effects on nutrient uptake and stress resistance, the plant transfers between 10 and 20 of its photosynthetically fixed carbon to the fungus (Finlay and Soderstrom 1992). However, despite the widely acknowledged significance of ECM fungi for plant growth, fitness and community composition particularly in difficult environments, their contribution to...

Development Of Transgenic Plants That Display Broad Resistance Against Pathogens

Genetic analysis of plant disease resistance has demonstrated that single R gene products control resistance by mediating specific recognition, either directly or indirectly, of complementary AVR proteins produced by pathogens. Plant breeders have often used R genes to introduce resistance into cultivated crops. However, the intro-gressed R genes, with only a few exceptions, have been shown to lack long-term durability in the field (Stuiver and Custers, 2001). Early evidence arose from studies on the rust fungi P. graminis f. sp. tritici and M. lini which suggested a possible relationship between the durability of R genes and pathogen variation Avr genes with low mutation rates corresponded to more durable resistance (Flor, 1958). Flor (1958) proposed that easily mutated Avr genes in pathogen populations were likely to be less critical to pathogen fitness than those that mutate rarely. Thus, if loss of avirulence function is associated with a

Responses of Neighboring Plants

Plants may gain a fitness benefit from responding to herbivore-induced volatiles from neighboring plants that are being attacked. Such a signal is indicative of the imminent danger, and the receiving plant may profit from exploiting this information by readying its defense (Dicke and Bruin 2001). Herbivore-induced plant signals can be exploited by neighboring plants of the same and of different species alike (Engelberth et al. 2004 Baldwin et al. 2006). Strong signals may immediately activate plant defenses, while lower (more common in nature) concentrations of signaling molecules can prime the plant for attack (Turlings and Ton 2006). This was nicely shown in a field study by Kessler et al. (2006) reporting that plant volatiles from damaged sagebrush plants can prime the induction of proteinase inhibitors in nearby tobacco plants. The primed tobacco plants received less damage from subsequent herbivore attack as compared to non-exposed control plants. Not only volatile emission, but...

Epistemic Status of the Developmental Systems

Here, we provide a way to translate the conceptual framework introduced in Sect. 12.3.1 into measurable phenomena and empirically based scientific knowledge. A DS can be modeled by a state space and the law of growth can be formulated in a such state-space. Usually, any system's goal is formulated as an attractor point or region in the state space of the properties of the systems or as a maximization or minimization of an index derived from the space parameters (e.g., ascendency in ecology). Here, we introduce the goal of growth through an underived variable (e.g., biomass) or set of variables (accounting for the life cycle of the organism) in the state space and the laws of growth through mathematical functions relating the numerical values of goal variable(s) and the numerical values of other parameters of the state space. We mention without demonstration that efficiency and effectiveness of the DS can be introduced from the form of these mathematical functions, and apparent and...

Ecological explanations

Excitement about the possible selective advantages of color production during leaf senescence was aroused from recent reviews (Hamilton and Brown, 2001 Archetti and Brown, 2004). Hamilton's reputation in evolutionary theory gave this hypothesis (now called a theory) all the more impact, and it was published nearly coincident with his untimely death in Africa. Hamilton and Brown postulated that brightly colored leaves during autumn could be a handicap signal, warning egg-laying insects against increased defensive compounds in those trees and reducing herbivory by newly hatched individuals the following year. They tested the hypothesis by a meta-analysis of the literature on aphid herbivory on trees. They found a significant repellent effect of yellow colors against aphids in the autumn, but not a significant association with red anthocyanic leaves. Evidence consistent with predictions of the hypothesis has been reported in two studies. In the mountain birch (Betula pubescens), Hagen...

Outcrossing and Inbreeding

Most vertebrate species consist of separate male and female individuals. In contrast, the majority of flowering plants are hermaphroditic, with both pollen and ovules produced by the same plant. As a consequence, many flowering plants are capable of self-fertilization (selfing), with seeds resulting from pollen and eggs produced by the same plant. The self pollen that fertilizes the egg may be produced by the same flower (called autogamy) or by different flowers on the same plant (geitonogamy). Selfing or mating among close relatives (inbreeding) often results in offspring that have reduced vigor and produce fewer offspring compared to offspring from matings between unrelated plants (outcrossing). This reduction in fitness of selfed offspring relative to outcrossed offspring is referred to as inbreeding depression. If both selfing levels and levels of inbreeding depression are high, natural selection may favor mechanisms that promote outcrossing. High levels of inbreeding depression...

The Role Of Mycorrhizae In Plant Primary Production

We saw in Chap. 2 how the saprotrophic fungal community in association with bacteria and soil fauna make mineral nutrients available for plant growth. Similar processes occur in both freshwater and marine ecosystems to provide nutrients for both pelagic and rooted vegetation. In both the terrestrial and, to a more limited extent, in freshwater and estuarine ecosystems, a symbiotic association between mycorrhizal fungi and plant roots influences the uptake of mineral nutrients from the substratum into plants for biomass production. This functional group of fungi have evolved along with their host plants and have a variety of ways in which they interact with both readily and poorly available nutrient resources to enhance plant growth. They are also important in protecting host plants against pathogens. In addition to these factors, these fungi may be more important than previously thought in influencing competition among component plant species of a plant community. This can occur by...

Addressing Insulin Resistance

Consumption of lower-GI foods and physical fitness will contribute to decreased insulin secretion and resistance, respectively. For patients who receive treatment for this syndrome, insulin regulation is indicated. Borrowing from our knowledge of treating diabetes with natural medicines, many of the same treatment principles may be applied as part of this treatment regimen, including consumption of specific nutrients via diet or supplementation. The remainder of this chapter concentrates on supplementation and exercise.

Gametophyte carbon and light stress relations

Fern gametophytes have intrinsic limitations for taking up and storing water, therefore, water relations may be an important area of gametophyte physiological ecology. As discussed above, and as will probably emerge from future studies, fern gametophytes are true poikilohydric plants. Poikilohydric taxa have evolved complicated morphological, biochemical, and anatomical mechanisms to cope with limited water and are robust in tolerating periods of drought. These plants face the additional complication of stress derived from exposure to excess light when their vegetative tissues experience reduced water contents. Light in excess of that which the photosynthetic machinery can transfer can result in photoinhibition (the light mediated depression of photosynthesis) and eventually significant photodamage (wholesale destruction of photosystems). Such depression can severely limit plant fitness. Low water content combined with excess light can be a deadly mix. Thus, even the most advanced...

Chemical Defense Based On Alkaloids

Overall, plants are quite capable of defending themselves from diverse microorganisms, herbivores, and other plants. Candidates for this protective role are their allelochemicals, which may possess deterrent repellent or toxic properties for a wide range of competitors.37 Included in the allelochemicals are the alkaloids, which are generally considered to be bitter (e.g., quinine, brucine) and in some cases very toxic (e.g., tetrodotoxin, batrachotoxin). Although at a glance the alkaloids appeared to be outstanding candidates to play defensive roles for their producers, they were initially described as secondary metabolites , as if their functions were not at all adaptive. Furthermore, plant-derived natural products were regarded as waste products that were equivalent to functionless molecules of little selective value.30 However, a concatenation of physiological, ecological, and chemical investigations has unambiguously established the critical role of alkaloids, for both survival...

Alkaloids For Defense And Exploitation

Concentrated in the seeds as an obvious means of promoting reproductive fitness.37 These seeds, which can contain 2-8 alkaloids, have long been utilized as human food, but only after they have been boiled to leach out the bitter and toxic QAs. However, this problem of purification was apparently solved by plant breeders who successfully produced sweet lupines, containing an alkaloid concentration of less than 0.01 , about 100 years ago. But although sweet lupines were indeed very palatable for humans, they were also a gustatory delight to a variety of herbivores. In the virtual absence of QAs, the sweet lupines were readily selected by rabbits and hares, as well as aphids, beetles, and thrips. On the other hand, the QA-fortified plants were almost untouched, clearly demonstrating that these alkaloids were highly active as deterrents for both vertebrate and invertebrate herbivores. It has been suggested that sometimes plant species must make a choice between two herbivorous...

Methods of Describing the Tradeoff Function

The second approach partitions phenotypic correlations into environmental versus genetic components and uses the genetic correlation between current and future reproduction to quantify the cost of reproduction (e.g., Geber, 1990). This is a labor-intensive approach, in that a large number of genetic families (clones, half-sibs, or full-sibs) that differ in reproductive output must be generated. However, it has a major advantage over the previous approach as environmental variation is no longer confounded with differences in reproductive output. Further, the measure of the reproductive cost that is obtained is directly relevant to evolutionary questions, since it is based on genetic variation that can be acted upon directly by selection (Reznick, 1985). The major drawback of this approach is finding sufficient genetic variation in reproductive output to assess reproductive costs. Given that traits closely related to fitness will be subject to strong selection pressure, there may be...

Simulations

Each simulation was started with a population of N individuals, heterozygous at the S-locus. This initial population had k S-alleles in equal frequencies. During each reproductive cycle, a new set of N individuals was created from the parental generation (Fig. 3.1). Each new offspring was formed by randomly selecting a parental individual as the maternal plant, and then allowing it to reproduce either clonally or sexually with probabilities c and 1 - c, respectively. We assumed no differences in any components of fitness among individuals or among sexual and clonal offspring (i.e. t 1), which in turn implies c 1 - y. For sexual reproduction, a new zygote was created by mating the maternal plant with a randomly selected pollen grain. All individuals, regardless of whether they reproduced by seed or vegetatively, contributed to the pollen pool. We assumed the complete expression of SI during the sexual component of the reproductive cycle. If the selected pollen was incompatible with the...

Induced Defenses and the Cost Benefit Paradigm

Defense costs are thought to be the raison d'etre for inducibility, by which costs are only incurred when a defense is needed. Costs can arise when resources are allocated to defenses and consequently not available for growth and reproduction, from the havoc that defenses might wreck with primary metabolism or the plant's ability to respond to other stresses, and from the damage caused by herbivores whose ability to resist plant defenses have been honed by constitutive defense expression. Though the cost-benefit paradigm is widely accepted, empirical evidence is rather slim. Elicitation studies, which elucidate fitness consequences of activating defense responses with elicitors, presented first conclusive evidence, but in these studies disentangling the costs of co-regulated responses is not possible. Quantitative genetics correlate changes in resistance and fitness among different genotypes, but defense-related traits can be genetically linked to other traits unrelated to defense....

Sulphurous Air Pollutants Occurrence and phytotoxicity

Chronic injury by S02 may be caused by (1) the negative consequences of acidification of tissue cells upon after the dissociation of the absorbed S02 (S02 + H20 H+ + HSO3 2H+ + S032 ) or, (2) by its reaction with cellular components that results in a disturbed metabolism, reduced growth and fitness. Visible injury at acute high levels of S02 may be the consequence of (1) severe cellular acidification or, (2) the direct effects of high endogenous toxic sulphite levels. Acute S02 injury also may be (3) the direct consequence of intracellular superoxide mediated free radical chain oxidation of sulphite to sulphate, which may occur in particular in the chloroplasts (De Kok 1990).

Mechanisms of herbicide resistance 1221 Target site resistance

A single mutation in the psbA gene coding for a 32-kD protein that forms part of the Photosystem II (PS II) complex in the thylakoids can lead to resistance to the herbicides that inhibit photosynthesis at PS II (Oettmeier, 1999). These single mutations cause resistance to a number of PS II inhibiting herbicides to varying degrees (see Table 5.2). In some cases 1000 times more herbicide is needed to displace QB from this site. As this binding site is common to many PS II inhibiting herbicides the cross-resistance observed is not surprising. However, cross-resistance does not always extend to all PS II herbicides as is clearly demonstrated in Table 5.2 . The mutation Ser264 Gly results in decreased binding and efficacy of triazines but not other classes of PS II inhibitors. The mutation Ser264 Thr results in a broader spectrum of resistance to phenylureas and the triazine herbicides, for example linuron and atrazine, respectively. Resistance to diuron and metribuzin is conferred by the...

Far RedMediated Perception of Neighboring Plants

Due to these constraints, plants may obtain fitness benefits by reducing their defense investments in situations when future competition is likely (Cipollini 2004) . Surprisingly enough, a connection between far-red sensing and defense induction has indeed been found in a native South American tobacco species, Nicotiana longiflora (Izaguirre et al. 2006) . Miriam Izaguirre and her colleagues exposed plants to either full sunlight or to light with far-red supplementation. Plants were grown in individual pots and thus were not in fact competing, but far-red supplementation to the lateral light mimicked the presence of competitors. Under these conditions, constitutive resistance to specialist herbivores was lower and defense induction was impaired even when the plants were actually being damaged. Additional experiments with tomato mutants that were defective in their far-red sensory systems made an involvement of phytochrome B in this defense suppression highly likely (Izaguirre et al....

Genetic Diversity And Virulence Development In The Nematode

Relatively rapid virulence selection has been demonstrated with M. incognita on cowpea with the resistance gene Rk (Petrillo and Roberts, 2005). Some, but not all, of the resulting virulent lineages displayed reduced fecundity on cowpea, indicating a trade-off between reproductive fitness and virulence. This is consistent with finding in other systems that avirulence genes function as pathogenicity factors and that overcoming resistance thus carries a cost to the pathogen (Bent and Mackey, 2007). In some cases, there appears to be an adverse cost of fitness for gain of virulence to Mi-1 in RKNs (Castagnone-Sereno et al., 2007 Roberts, 1995), suggesting that here, too, the avirulence gene may correspond to a pathogenicity factor.

Dynamic View of Costs and Benefits of Induced Responses

In summary, though many theories about the ecology and evolution of plant defenses are based on tradeoffs between costs and benefits, the evidence for costs is scarce. This is due to the difficulties of separating the fitness costs of a specific defense trait from genetically, metabolically, and functionally linked traits. Methodological advances allow the genetic background and genetic linkage to be controlled for, but The simplistic view of induced defenses - that an initially constitutively expressed defense evolves to become inducible so as to minimize the defense costs when the defenses are not needed - is difficult to harmonize with the complex and flexible nature of plant metabolism. The diverse linkages among various responses to herbivory suggests that a more dynamic view of the costs and benefits of induced defense would be more appropriate. The fitness of a plant depends on internal and external factors (Fig. 3.3A). The latter are the environmental conditions including...

Evolutionary Considerations

Although at least some mechanistic aspects of airborne resistance induction are now well understood at the physiological and even the genetic levels, our knowledge about the fitness effects on both partners involved is surprisingly restricted, and information on the evolutionary consequences of plant-plant communication as well as on its evolutionary origins is apparently lacking. Surprisingly enough, it appears that this interaction usually benefits the receiver, and normally even at the cost of the emitter. Most plants use the information on the presence of (damaged) neighbors to adapt their growth and defensive phenotype according to current environmental conditions (i.e., enemy pressure and competition). Airborne plant-plant communication thus benefits only the receiver in most cases. Since plants usually compete with each other for light, space, water and nutrients, it can even be expected that this communication has detrimental effects on the emitter, which is already damaged....

Defining the Components of Competitive Ability for Betweenspecies Plant Competition Lessons from Withinspecies

For a single population at equilibrium density, where births are balanced by deaths and biomass is at carrying capacity (i.e., competition is intense), we know, by definition, that the average plant leaves exactly one descendant. Yet, as Harper (1977) suggested, it is an intriguing paradox that natural selection continually favors individuals that leave more. We know, therefore, that high fitness (number of descendants) within this population is determined ultimately by relatively high lifetime output of reproductive offspring (i.e., offspring that become reproductive), despite intense lifetime intraspecific competition. Other traits (e.g., large size) may contribute but ultimately, natural selection recognizes only one currency offspring production (Pianka, 1988). The benefit of producing more than one reproducing offspring (higher fitness) is always enjoyed exclusively by the parent plant. In natural vegetation, however, as in Hardin's (1968) tragedy of the commons, the cost of this...

Cost Benefit and the Symbiotic Continuum

Central to this discussion is the evaluation of what are costs and benefits in mycorrhizae, and the degree to which the benefits exchanged are by-products or costly to the symbionts (Herre et al. 1999 Hoeksema and Schwartz 2002 Hoek-sema and Kummel 2003 de Mazancourt et al. 2005). Mycorrhizae can have multiple nonnutritional effects on the host plant that may determine increased survival and fitness such as protection against root and shoot pathogens (e.g., Akema and Futai 2005), protection from toxic minerals (e.g., Hildebrandt et al. 2007 see Chaps. 14 and 18 in this volume), or resistance to drought (e.g., Bogeat-Triboulot et al. 2004). However, it is generally considered that the main benefit to the plant from mycorrhizae is an improved nutrition, while the cost is the C expended in growth and maintenance of the fungus. The outcome of the relationship is presumed to depend on the balance between the two, and negative effects of mycorrhizal colonization are expected to occur when...

Transgene Containment

The expansion of transgenic crops has raised concerns about the flow of transgenes to nearby cross-compatible crops and native plants (Daniell 2002 Chapman and Burke 2006 Lee and Natesan 2006 Brunner et al. 2007). Many factors influence transgene flow, including dispersal via seeds, pollen, or vegetative propagules (Brunner et al. 2007), and the fitness of the plants resulting from genetic exchange with the transgenic crop (Chapman and Burke 2006 Lee and Natesan 2006). No single strategy of containment will be 100 effective in any situation, and the best combined approaches must be determined on a case-by-case basis (Chapman and Burke 2006 Lee and Natesan 2006). Pollen sterility can make a significant contribution toward transgene containment (Brunner et al. 2007). This strategy is suited to species amenable to vegetative propagation, and has been applied to creeping bentgrass (Luo et al. 2005). The maize Plus-Hybrid system can also be adapted to limit transgene flow, through use of a...

Leaf Trichome Formation and Plant Resistance to Herbivory

Leaf trichomes contribute to plant resistance against herbivory. In several plant species, the trichome density of new leaves increases after herbivore damage. Here we review the genetic basis of trichome production and the functional and adaptive significance of constitutive and induced trichome formation. We focus on leaf trichomes and their production in response to damage caused by herbivores. The genetic basis of trichome production has been explored in detail in the model species Arabidopsis thaliana. Recent comparative work indicates that the regulatory networks governing trichome development vary and that trichome production has evolved repeatedly among angiosperms. Induced trichome production has been related to increased levels of jasmonic acid in Arabidopsis, indicating a common link to other changes in resistance characteristics. Damage from insect herbivores is oftentimes negatively related to trichome production, and enhanced trichome production may thus be advantageous...

Interactions Between Plants and Animals

Initial research on plant-animal relations was at the level of individual organisms. Various types of relations were found, e.g. mutualistic relations, where both partners profit, such as animals visiting flowers for nectar or pollen leading to pollination and fruit set. Also there are parasitic relations as well as interactions of advantage to one partner and disadvantage to the other such as herbivory or carnivory. Various forms are distinguished Neutralism where no partner suffers loss of fitness (e.g. chance, random visit to flowers) amensalism where one partner suffers (e.g. visit to rob flowers of seeds) commensalism where one partner is advantaged without negative influences on the other (e.g. visits to flowers as meeting places). Figure 4.3.6 shows three examples of the diversity of relations between plants and animals.

Detoxification of the soil environment

Both laboratory studies referred to earlier and analyses of growth in heathland soil indicate that the roots of ericoid plants such as Calluna are extremely sensitive to the presence of low levels of the organic and metallic compounds which are widely distributed in acid heathland soils. In the absence of mycorrhizal infection, complete inhibition of root growth can occur. Under these circumstances, which have been described as a toxicity syndrome (Read, 1984), it is evident that physico-chemical rather than nutritional constraints are of primary importance in determining survival, and hence fitness , in the environment.

Spatial Distribution of Secondary Compounds Within a Lichen Thallus and Optimal Defense Theory

Reproductive structures like soralia often produce lichen compounds other than the remaining thallus (e.g. Imshaug and Brodo 1966 T0nsberg 1992 Nybakken et al. 2007). Snails avoid soralia in Pseudocyphellaria crocata (Gauslaa 2008) and L. scrobiculata (Asplund et al. 2010c). In the latter species, the snail C. laminata avoided the soralia and grazed on vegetative tissues of control thalli. However, after acetone rinsing, C. laminata instead preferred the soralia (Fig. 7 Asplund et al. 2010c). The soralia contained five times more m-scrobiculin than the vegetative thallus parts, but soralia had almost no usnic acid compared with the vegetative parts. By adding m-scrobiculin and usnic acid to filter paper fed to the snails, it was shown that m-scrobiculin efficiently deterred grazing, whereas usnic acid had almost no deterring effect (Asplund et al. 2010c). Therefore, L. scrobiculata allocates its most efficient grazing-deterrent compound to reproductive parts that likely are most...

Origin and evolution of polar cryptogamic floras

The position is also different in cryptogamic floras, particularly bryophytes, in which the proportion of polar endemics is relatively low (Chapter 1). It thus seems even more likely in the case of cryptogams than of higher plants that the majority of species originated before the retreat of forests and other temperate vegetation, their occurrence in the tundra reflecting tolerance of polar environments rather than evolution in response to the selection pressures exerted by such conditions. This view is consistent with the fact that many of the physiological attributes of polar bryophytes and lichens that appear to confer fitness in severe environments are also to be found among temperate species (Chapter 5).

Ericoid mycorrhizal infection and metal toxicity

Which to identify a mycorrhizal relationship, may itself come to be called into question. In natural ecosystems it is likely to be at least as important to consider reproductive capability or survivorship as indicators of fitness and there is little doubt that, in future, experiments with mycorrhiza will turn increasingly to investigating the hypothesis that the infection is involved at these deeper levels, to ensure survival of the individual components of the community, and hence to sustain the ecosystem itself.

Plant Ecology Introduction

Haeckel included in the science of ecology the areas physiology, morphology and chorology (the science of the distribution of organisms) to understand the conditions for existence and adaptation . In this book, we try to comply with Haeckel's understanding of plant ecology and to include the breadth of ecology as it was demanded by Haeckel. Adaptation to the environment starts at the molecular and cellular level where environmental conditions are detected and the responses to changes in the environment are accomplished. Starting from these physiological mechanisms, the morphological characteristics of organisms plants become important at the level of the whole plant. Cellular metabolic reactions and structural (morphological and anatomical) organisation are the biological tools with which organisms make use of certain environmental conditions, avoid them or adapt to them. The combination of physiological and morphological adaptation is particularly important for plants, as they are...

The Arbuscular Mycorrhizae

Contamination, which can be caused by essential elements in excessive concentrations, by toxic elements and ions or by other organic or inorganic pollutants, which may result from either human activities or natural processes. Many researchers have shown that AM promotes plant fitness under a variety of stress conditions and through various mechanisms. Some of these mechanisms are non-specific, and include enhanced nutrient acquisition and, frequently, enhanced plant growth, regulation of the plant hormone balance, and improving rhizospheric and soil conditions. In addition, AM improves plant growth tolerance with more specific mechanisms in relation to the kind of stress.

Balancing Selection Results from Indirect Recognition

Monitoring the virulence function of Avr proteins, because structural modification of an Avr protein by mutations cannot escape R recognition unless the virulence function is affected. A likely outcome is the deletion of the Avr gene in the pathogen to avoid R-dependent resistance. However, if that virulence activity is important for the pathogen, loss of the Avr could incur a penalty in fitness for the pathogen. In this case, natural selection would balance the benefit (enhanced virulence) and cost (elicited resistance) of keeping this Avr gene in the pathogen population, resulting in a balanced polymorphism at the Avr locus. Likewise, while expression of the R gene has an obvious benefit for the host in the presence of the cognate Avr-expressing pathogen, it may incur a cost of resistance in the absence of the pathogen (Tian et al. 2003). Thus natural selection would also favor a balanced polymorphism at the R locus (Van der Hoorn et al. 2002). The most likely outcome of this R-Avr...

Plasticity of Meristem Allocation

Schmitt's (1993) study on Impatiens capensis (Balsaminaceae), an annual herb, demonstrated that there may be among-population variation in phenotypic plasticity of meristem allocation. One of the study populations came from an open habitat and the other one from a shady environment. Genotypes of both populations were grown in both high and low light. The time of anthesis was plastic for plants from the sunny population. In high light, flowering was delayed and meristems were allocated to branching in the early development of plants from the sunny population. In low light, flowering was early and branches fewer, resulting in a negative association between early reproductive allocation and later growth. Plants from the shady population started to flower earlier than plants from the sunny population, and the time of anthesis was not sensitive to light treatment. Light treatment did not affect branching of plants of the shady population. Donohue et al. (2000a,b, 2001) used...

Influence of microhabitat

Longino (1986) questioned the notion of coevolution between ants and nest-garden plants. The presence of seed lures is not convincing because all myrmecochoric species produce them. Moreover, nest-garden plants may actually reduce ant fitness by clogging brood chambers and slowing temperature-dependent larval development through shading. Extensive root development eventually drives large ant species from nests dominated by certain robust acaulescent (stemless) Anthurium and bromeliad specimens (Fig. 5.11). Habitual poor housekeeping constitutes the best case for specific adaptation among plant-feeding ants (Janzen 1974, but see Davidson and Epstein in press). Iridomyrmex cordatus supposedly packs nutrient-rich refuse in absorptive chambers of Hydnophytum and Myrmecodia tubers in contrast to the habit of ejecting debris purportedly practiced by ants that simply protect their botanical partners.

Genetic Engineering Versus Traditional Tree Breeding

Substantial environmental damage could occur if the transgene increases the fitness of the host tree under wild conditions (Raffa 1989, James 1997, Raffa et al. 1997, DiFazio et al. 1999). The longevity of the escaped GM tree may be greater than that of the original non-GM tree, resulting in increased probability that GM trees could establish in the wild or interbreed with non-GM trees. Hypothetically, GM trees could be more invasive than non-GM trees, thus outcompeting native host trees for available resources. This also could happen if GM trees exhibited an increased growth rate, reaching reproductive maturity earlier than non-GM trees. One way to combat this might be to genetically engineer reproductive sterility. The research group led by Dr. S. H. Strauss at Oregon State University is working on this issue, and has inserted some transgenes that may give sterility (Strauss et al. 1995). This could solve many of the risks associated with the deployment of GM trees.

Applied Aspects Of Bee Pollen

The bee-gathered pollen is pressed into tablets or sold loose, but some companies add a binder of honey and concoct pollen bars-said to have been a favourite of Ronald Reagan (former American President). In Engelholm, Sweden, the Cernelle Company has been making pollen extract products since 1952. Cernelle manufactures a pollen toothpaste, pollen face cream, pollen animal feed and scores of other concoctions. These pure pollen, i.e., usually pollen of same species of plants are consumed in different forms for physical fitness and instant energy. Joggers often eat pollen tablets for general fitness. Pollen are extensively used in health food supplements as their medicinal use was known to man since prehistoric times. Pollen tablets as a nutritional supplement are available in the market (Fig. 12.13). Pollen in liquid form is also available commercially. Pollen is known to possess antibiotic properties and also recommended for certain problems of intestinal functions, respiratory system...

Plant Quality and Nursery Production

It is imperative that the planting stock used in any project, whether for commercial forestry or amenity planting, is of the best possible quality, especially in view of the financial investments (Fig. 9.1 and 9.2). But how do we define quality Obviously quality is very variable and difficult to define precisely, since it is dependent on many factors and features of the plant, the site and on the objectives of the planting. Harris et al. (2003) state that there is no perfect tree. Selection is a compromise among the proposed function of the plants, its adaptation to the site and the amount of care it will require. The relative importance of a particular characteristic will vary as a function of the specific site and management situation. Langerud (1991) proposed the adoption of Willen and Sutton's (1980) definition, i.e. ' The degree to which that stock realizes the objectives of management (to the end of the rotation or achievement of specific sought benefits) at minimum costs....

Architecture and nutritional economy

More succinctly, economies of time and material inherent to the body plan of the Type Five bromeliad should promote fitness wherever drought or infertility slow carbon gain and scattered safe sites, disturbance or any other agency that kills large numbers of pre-reproductive individuals mandate compensatory (elevated) fecundity (Benzing 1978a). Dry-growing Tillandsia experience some of the most stressful (nonproductive) of all the environments colonized by land flora, and they often root on unstable media that mandate rapid plant cycling. Small, mobile seeds, a consistent characteristic of Tillandsioideae, also accord with the scattered and ephemeral nature of bark, which is the substrate these plants use more frequently than any other.

Allometry Theory and RA

Clearly, the application of allometry theory to the principle of allocation is fraught with difficulty, given the diversity of plant life forms and morphological structures. Models of resource allocation to sexual reproduction in clonal plants capable of vegetative reproduction must consider the relative costs and benefits of producing sexual versus asexual propagules (Armstrong, 1982 Loehle, 1987 Bazzaz, 1997). From a practical standpoint, plant size may be difficult to define for large, perennial herbs that produce numerous ramets, and sexual reproduction may not necessarily be related to long-term fitness. For woody plants, size may not be meaningful for allo-metric research because of the massive investment in nonliving, supporting structures. Unfortunately, most models to date do not incorporate the costs of producing supporting structures (e.g., the rachis of an inflorescence) or the carbohydrate costs of storage organs (e.g., roots or corms). Wagner, 1989). A decrease in RA...

Signaling Events During CAM Modulation by Water Availability

Calcium Signal Aba

As with other environmental stresses, water limitation can promote changes in absolute concentration and distribution of plant hormones, which in most cases results in significant changes in the balance between distinct hormonal classes. Generally, water deficit stimulates abscisic acid (ABA) synthesis and inhibits cytokinin (Ck) production in the roots, thus affecting the supply of these hormones to the leaves via transpiration stream (Pospisilova et al. 2005). As a result, the balance between ABA and Cks in foliar tissues represents an important mechanism controlling physiological responses (e.g., the stomatal closure) that culminate in higher adaptive fitness for the whole plant (Hare et al. 1997 Pospisilova et al. 2000, 2005 Tanaka et al. 2006). According to the available data, ABA and Cks are also considered the two major hormonal classes controlling CAM expression, and it is currently speculated that these two hormones might indeed act as root-derived messengers responsible for...

Oxygen Evolving Complex Associated Proteins

Cyanobacteria, green algae, or spinach have a single-copy psbO gene. Sequencing of the Arabidopsis genome (AGI 2000) revealed the existence of two genes coding for two distinct proteins (PsbO1 and PsbO2), which differ only by ten amino acid residues in the mature forms. The expression of these proteins in Arabidopsis was confirmed by proteomic analyses of the thylakoid lumen (Peltier et al. 2002 Schubert et al. 2002). Both genes are expressed in wild-type plants, while the PsbO1 protein is about fourfold more abundant than PsbO2 (Murakami et al. 2002 Lundin et al. 2007b). The lower expression of PsbO2 indicates a regulatory rather than a structural role for this isoform in the function of PSII. Simultaneous RNAi-based suppression of psbO gene expression in Arabidopsis has confirmed the importance of PsbOs for PSII stability and photoautotrophy in plants (Yi et al. 2005). Notably, Arabidopsis mutants with a disrupted psbOl gene display an upregulation of psbO2 expression without...

Signalling Associated with Synthesis of Bioprotective Metabolites

Four main classes of biologically active metabolites have been identified in grass hosts infected with E. festucae peramine, indole diterpenes (principally lolitrem B), ergot alkaloids (principally ergovaline) and lolines. Peramine is a potent feeding deterrent of adult Argentine stem weevil (ASW Listronotus bonariensis), an economically important pest of L. perenne in New Zealand agricultural ecosystems. Lolitrem B also has biological activity against some insect larvae but is better known as the causative agent of ryegrass staggers , a neuromuscular disorder that affects animals grazing on pastures with high toxin levels. Although the fitness benefits of ergot alkaloids are still to be defined, they are implicated in herbivory protection against some insects and nematodes. However, ergot alkaloids are best known for

Hostmistletoe crypsis

Resemblance is greatest among species pairs occupying arid rather than humid parts of Australia (Barlow and Wiens 1977). Excluding the mistletoes from everwet northeastern forests (which show relatively broad host specificity) and the two endemic terrestrials, 78 of Australian loranths bear foliage resembling that of their hosts too closely for coincidence. Barlow and Wiens and others before them have postulated that vegetative similarity constitutes genetically based mimicry which has arisen independently many times in response to selective pressures and confers fitness by hiding mistletoe foliage within matrices of less palatable forage. Leaf form is supposedly especially convergent in Australia because the two dominant tree genera -Acacia and Eucalyptus - have become so well defended (i.e., relatively unpalatable because of sclerophyllous leaves containing the essential oils of Eucalyptus and the phenolics of Acacia) that the parasites have become attractive food items. Mistletoes...

Population Structure and Reproductive Strategies

Eat The Elephant

Proved challenging using standard ecological approaches. The clonal growth form of many seagrass species results in a hierarchy of different organisational levels. The most elementary level of organisation is the ramet (sensu Harper, 1977), the potentially independent individual. In seagrasses, this individual typically is the leaf bundle, a piece of rhizome, and a root bundle (Tomlinson, 1974). Depending on the longevity of rhizome connections between ram-ets, several ramets can form physiologically integrated clusters, the second level of organization. The size of these clusters varies greatly between species, and may comprise several hundreds of leaf shoots in the genus Posidonia. The sexual individual, or genet, are all ramets or ramet clusters which originated from the same zygote. From an evolutionary point of view, it is only the genet that matters and eventually transmits genes to the next generation. Since genets may be exceedingly large, the determination of genet fitness,...

Cell Axis and Plant Development

The architectural response of plant evolution to the challenges of mechanical load had a second consequence, namely, a completely sessile lifestyle. This immobility, in turn, determined plant development with respect to its dependence on the environment. During animal development, body shape is mostly independent of the environment. In contrast, plants have to tune their Bauplan to a large degree to the conditions of their habitat. Morpho-genetic plasticity thus has been the major evolutionary strategy of plants to cope with environmental changes, and fitness seems to be intimately linked to plant shape (Fig. 1).

Costs of Reproduction

We have shown that reproduction lowered the rate of biomass production and shortened the total life period by inducing senescence of the whole vegetative body. These negative effects of reproduction on subsequent growth and survival have been termed as costs of reproduction (Williams, 1966). It has been suggested that plants maximize their fitness by minimizing the cost of reproduction (Reekie and Bazzaz, 1992 Bazzaz, 1997). The cost of reproduction has been classified into two categories direct costs of reproduction, i.e., resource allocation at the time of reproduction, and indirect costs, referred to as indirect, delayed, or demographic costs of reproduction (Bazzaz and Reekie, 1985 Obeso, 2002). Direct costs are commonly referred to as the current reproductive efforts, which are assessed by the fraction of resources allocated to reproductive structures. Indirect costs are assessed by the reduction in survival (survival costs) and in fecundity (fecundity costs), where current...

Effects on Tritrophic Interactions

Leaf trichomes do not only affect herbivores, but also their natural enemies. This may indirectly affect the intensity of damage caused by herbivores. In theory, the effect on the abundance and effectiveness of natural enemies may be neutral (no effect), negative or positive (Fig. 4.1). If we assume that herbivores are affected negatively by leaf trichomes (Fig 4.1 top graph), a neutral effect on the third trophic level will result in natural enemies having an additive effect on plant damage caused by herbivores and on plant fitness. A negative effect on the third trophic level will act antagonistically. Depending on the relative strength of the negative effects of leaf trichomes on herbivores and natural enemies the correlation between trichome density and damage may vary from negative to positive. Plant damage will be (i) negatively correlated with trichome density if the effect on natural enemies is weaker than that on herbivores (dotted line) (ii) uncorrelated with trichome...

Other components of forest ecosystems

Pathogens are major determinants of plant fitness (Burdon, 1987). Therefore, any effects of UV-B radiation on pathogenic organisms have the potential to influence the responses of plants to increased UV-B. The impacts of UV-B on pathogens can take two forms either directly, by effects on the pathogen itself, or indirectly, through effects on the host which then influence interactions with the pathogen (Manning & Many studies have shown direct effects of UV-B radiation on the germination of fungal spores. For example, Semenuik and Stewart (1981) demonstrated that a four-fold increase in UV-BTHIM (biologically effective UV-B weighted with the generalised plant action spectrum of Caldwell (1971) fitted with the mathematical function of Thimijan, Cams and Campbell (1978) and normalised at 300 nm above ambient levels), reduced the infection of a cultivated Rosa sp. by black spot (Diplocarpon rosae Wolf.) between 6 and 18 h after inoculation with the fungus, which was attributed to the...

Exercise

Declining testosterone has multifaceted origins and levels of the hormone can be augmented in numerous ways. Perhaps the most neglected medicine of all, exercise can improve an aging man's testosterone levels (in addition to offsetting andropause-related bone loss, weight gain, muscle loss, and sleep and mood disturbances). Moderate physical activity was shown to increase serum testosterone levels by 39 , SHBG by 19 , free testosterone by 23 , and total serum proteins by 13 , mainly during a period of exercise in one study.26 The transient elevation of testosterone observed in this study was thought to be partly the result of increased SHBG concentration. Testosterone levels returned to baseline in the subjects after the exercise, indicating that hemoconcentration may have contributed partially to the subjects' increased testosterone levels. However, a separate study sought to challenge the observation that perhaps this testosterone elevation was only related to increases in SHBG...

Mating Systems

Mating system estimates provide a more detailed understanding of population processes such as small scale gene flow, the frequency of inbreeding and estimates of inbreeding depression (e.g. Ruckelshaus, 1995 Hammerli and Reusch, 2003b). The consequences of inbreeding can significantly impact a species primarily due to reduction in progeny fitness (Charlesworth and Charlesworth, 1987 Ellstrand and Elam, 1993). For this reason alone, estimates of inbreeding are valuable and should be obtained for a greater range of seagrass species.

Population genetics

Wagenius (2000) studied the diversity and fine-scale population substructure (by mapping individual plants within subpopulations) of wild E. angustifolia in a fragmented prairie region of western Minnesota. He found a strong positive linear correlation of several important estimates of genetic diversity (proportion of polymorphism, allelic richness, and gene diversity) with population size, that is, the smaller the population, the less diversity (Wagenius, 2000). Small local populations also had more spatial genetic structure, indicating a reduction in random mating (Wagenius, 2000). Wagenius (2000) concluded that small population size was a factor in lowered fitness as measured by pollen limitation (the absence of compatible pollen inferred from style persistence) and progeny vigor. It would be interesting to see how values of genetic identity and interpopulation distances as measured by other molecular markers compared to these results.

New Perspectives

A high fitness penalty of Avr genes in the pathogen could be used for predicting the durability of the cognate R genes (Leach et al. 2001), as a high fitness penalty would set constraints for Avr genes to escape from R recognition. But it may not be accurate in situations where Avr genes directly recognized by R genes may evade recognition by mutations that do not necessarily affect its virulence function (see Section 6.1). Also it may be practically difficult to assess the fitness penalty of Avr genes. One of the most exciting inferences from R-Avr coevolution is that R-Avr indirect recognition leads to stable balanced polymorphisms at the R and Avr loci (Table 2), which implies that R genes of this category are likely to be durable. Even though this rule needs to be vigorously tested with more R and Avr pairs, it gives a promising molecular tool to identify and predict durable R genes that guard critical virulence targets based on the feature of the sequence...

Concluding Remarks

Figure 1.5 The role of fungi in carbon cycling as proposed by Harley (1971). The left side of the model is driven by fungal symbionts and pathogens, which directly utilize plant photosynthates. The right side of the model represents the decomposition cycle, utilizing dead plant and animal parts. Open arrows at the top indicate feedback effects on photosynthesis (plant fitness). Figure 1.5 The role of fungi in carbon cycling as proposed by Harley (1971). The left side of the model is driven by fungal symbionts and pathogens, which directly utilize plant photosynthates. The right side of the model represents the decomposition cycle, utilizing dead plant and animal parts. Open arrows at the top indicate feedback effects on photosynthesis (plant fitness).

Meristem Models

We can evaluate by means of mathematical models how meristem allocation patterns affect individual fitness. Development and structure of meristem systems produce regular patterns that make them amenable to modeling. Meristem systems resemble structured populations, where different meristem states correspond to different types of individuals. Models derived from It is possible to use an analytical approach to the problem. If a plant without reproduction has Nt-1 growing meristems at time t -1 and each meristem contributes to the meristem number at the next time step by, on average, n meristems, the number of meristems at time t will be Nt nNt-1. In reproductive plants, a fraction r ( n) of the meristems are allocated to reproduction. In this case, Nt (n - r)Nt-1. If one reproductive meristem produces k seeds, the reproductive output at time t is Rt krNt. The total fitness up to time t, Wt, can be calculated as a sum of Ris where i 1 t. The coefficient n includes both the average...

Top Down Control

The Red Queen Hypothesis (RQH) was originally formulated as a species extinction law (Van Valen 1973), and has since been developed and expanded to include a range of ecological aspects of host-parasite interactions. The hypothesis is based on the Red Queen character of the Lewis Carroll book 'Through the Looking Glass', saying to Alice 'here, you see, it takes all the running you can do to keep in the same place'. The RQH attempted to reconcile the biotic (and genetic) aspects of interactions between organisms with the environmental parameters that result in natural selection and evolution (Van Valen 1975). In order to avoid (local) extinction, the organisms at loss must evolve rapidly to improve their fitness, and this process is occurring continuously (Van Valen 1973, 1976). As the host is also the physical environment of the parasite, at least for part of its life-cycle, the RQH effect would be more pronounced if the organisms in question were a host improving in fitness, and a...

Fitness Fundamentals

Fitness Fundamentals

Everyone knows that good health is something to be treasured and respected, but few make a conscious habit to pay attention to their health until the red flag appears which in most cases signifies really poor health conditions. Get fit with the info here.

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