Phylogeny and Evolution of Nematodes

Wim Bert, Gerrit Karssen and Johannes Helder

3.1 Introduction

A phylogenetic framework is needed to underpin meaningful comparisons across taxa and to generate hypotheses on the evolutionary origins of important properties and processes. In this chapter we will outline the backbone of nematode phylogeny and focus on the phylogeny and evolution of plant-parasitic Tylenchomor-pha. We will conclude with some recent insights into the relationships within and between two highly successful representatives of the Tylenchomorpha; the genera Pratylenchus and Meloidogyne.

3.2 Backbone of Nematode Phylogeny

The phylum Nematoda can be seen as a success story. Nematodes are speciose and are present in huge numbers in virtually all marine, freshwater and terrestrial environments. Analysis of large EST data sets recently reconfirmed the placement of the phylum Nematoda within the superphylum Ecdysozoa (Dunn et al. 2008), a major animal clade proposed by Aguinaldo et al. (1997) that unites all moulting animals.

Blaxter et al. (1998) (53 taxa) and Aleshin et al. (1998) (19 taxa) were among the first to exploit the potential of small subunit ribosomal DNA (SSU rDNA) sequence data to resolve phylogenetic relationships among nematodes. Holterman et al. (2006) presented a subdivision of the phylum Nematoda into 12 clades based on a series of mostly well-supported bifurcations in the backbone of the tree (339 taxa) (Fig. 3.1). The under-representation of marine nematodes in these phylogenetic overviews was, to some extent, lifted by SSU rDNA-based papers from Meldal et al. (2007) and Holterman et al. (2008a). Recently, a phylogenetic tree based on

Nematology Unit, Department of Biology, Ghent University, Ledeganckstraat 35, 9000 Ghent, Belgium e-mail: [email protected]

J. Jones et al. (eds.), Genomics and Molecular Genetics of Plant-Nematode Interactions, 45 DOI 10.1007/978-94-007-0434-3_3, © Springer Science+Business Media B.V. 2011

Trophic ecology entomopathogen animal parasite jjZ^ fungivore ^ plant parasite j 0o bacteriovore algivore omnivore predator see Fig. 2

Tylenchomorpha

Clade 11 Cephalobomorpha

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