[
WormBook,
2006]
In the last decade, nematodes other than C. elegans have been studied intensively in evolutionary developmental biology. A few species have been developed as satellite systems for more detailed genetic and molecular studies. One such satellite species is the diplogastrid nematode Pristionchus pacificus. Here, I provide an overview about the biology, phylogeny, ecology, genetics and genomics of P. pacificus.
[
WormBook,
2005]
The knowledge about C. elegans provides a paradigm for comparative studies. Nematodes are very attractive in evolutionary developmental biology given the species richness of the phylum and the easiness with which several of these species can be cultured under laboratory conditions. Embryonic, gonad, vulva and male tail development were studied and compared in nematodes of five different families, providing a detailed picture of evolutionary changes in development. In particular, vulva development has been studied in great detail and substantial differences in the cellular, genetic and molecular mechanisms have been observed between C. elegans and other nematodes. For example, vulva induction relies on the single anchor cell in C. elegans, whereas a variety of different cellular mechanisms are used in related species. In recent years, a few species have been developed as satellite systems for detailed genetic and molecular studies, such as Oscheius tipulae and Pristionchus pacificus.
[
1996]
In the nematode model organism Caenorhabditis elegans developmental processes can be anaylzed at various levels. The invariance of cell lineage allows a high-resolution morphological description of development and an experimental approach by ablation of individual cells. Isolation and characterization of genetic mutations reveal the basis of the genetic program underlying particular developmental processes. DNA-mediated transformation can be used to anaylze the function of cloned genes and thus finally generate also a molecular understanding of the process under investigation. Evolutionary approaches to development are rare and so far consist only of a subset of techniques used in the reference model system. By using the complete set of techniques from the model organism, including genetics, in related but morphologically distinct species, one can get a detailed comparison of a developmental process. Here we describe our attempt to establish the techniques known in the model organism Caenorhabditis of the Rhabditidae in other free-living nematodes, including Pristionchus pacificus of the
[
WormBook,
2005]
C. elegans is a member of a group of nematodes called rhabditids, which encompasses a large number of ecologically and genetically diverse species. A new, preliminary phylogenetic analysis is presented for concatenated sequences of three nuclear genes for 48 rhabditid and diplogastrid species (including 10 Caenorhabditis species), as well as four species representing the outgroup. Although many relationships are well-resolved, more data are still needed to resolve some key relationships, particularly near the base of the rhabditid tree. There is high confidence for two major clades: (1) a clade comprising Mesorhabditis Parasitorhabditis, Pelodera, Teratorhabditis plus a few other species; (2) a large clade (Eurhabditis) comprising most of the remaining rhabditid genera, including Caenorhabditis and its sistergroup Protorhabditis-Prodontorhabditis-Diploscapter. Eurhabditis also contains the parasitic strongylids, the entomopathogenic Heterorhabditis, and the monophyletic group Oscheius which includes the satellite model organism O. tipulae. The relationships within Caenorhabditis are well resolved. The analysis also suggests that rhabditids include diplogastrids, to which the second satellite model organism Pristionchus pacificus belongs. Genetic disparity within Caenorhabditis is as great as that across vertebrates, suggesting Caenorhabditis lineages are quickly evolving, ancient, or both. The phylogenetic tree can be used to reconstruct evolutionary events within rhabditids. For instance, the reproductive mode changed multiple times from gonochorism to hermaphroditism, but only once from hermaphroditism to gonochorism. Complete retraction of the male tail tip, leading to a blunt, peloderan tail, evolved at least once. Reversions to unretracted tail tips occurred within both major rhabditid groups. The phylogeny also provides a guide to species which would be good candidates for future genome projects and comparative studies.