Abstract
BackgroundThe nematode Pristionchus pacificus has originally been developed as a satellite organism for comparison to Caenorhabditis elegans. A 10X coverage of the whole genome of P. pacificus is available, making P. pacificus the first non-Caenorhabditis nematode with a fully sequenced genome. The macroevolutionary comparison between P. pacificus and C. elegans has been complemented by microevolutionary studies of closely related strains and species within the genus Pristionchus. In addition, new understanding of the biology of Pristionchus from field studies, demonstrating a close association with various scarab beetles and the Colorado potato beetle, supports consideration of this nematode in studies of ecosystems. In the course of field studies on four continents more than 1,200 isolates were established from 15,000 beetle specimens representing 18 Pristionchus species. Two remarkable features of the Pristionchus – beetle association are the high species specificity of the interaction and the interception of the beetle's sex communication system for host recognition by the nematodes, as suggested by chemotaxis studies. Evolutionary interpretations of differences in developmental, behavioral and ecological patterns require a phylogenetic framework of the genus Pristionchus.ResultsHere, we provide a robust phylogeny of all 18 available Pristionchus species based on a set of 27 ribosomal protein genes encompassing a total of 10,971 bp. The phylogenetic tree provides evidence for North American and European clades, which are embedded in a deeper clade that includes Asian species. It also indicates putative invasion events. Of the 18 Pristionchus species, 13 are gonochoristic and five are hermaphroditic. The phylogeny indicates that all hermaphroditic species have arisen independently within the genus Pristionchus.ConclusionCombined ribosomal protein cDNA data can provide the basis for reconstruction of a robust phylogenetic framework for microevolutionary and biogeographic analyses. An additional major implication of our studies is the use of Pristionchus for nematode biodiversity assessments. While some species are represented by more than 100 isolates, others were found less than four times. Such patterns were observed on all continents and in all phylogenetic clades indicating that species asymmetry is a widespread phenomenon, which can now be further investigated by molecular tools.
Highlights
The nematode Pristionchus pacificus has originally been developed as a satellite organism for comparison to Caenorhabditis elegans
Combined ribosomal protein cDNA data can provide the basis for reconstruction of a robust phylogenetic framework for microevolutionary and biogeographic analyses
Such patterns were observed on all continents and in all phylogenetic clades indicating that species asymmetry is a widespread phenomenon, which can be further investigated by molecular tools
Summary
The nematode Pristionchus pacificus has originally been developed as a satellite organism for comparison to Caenorhabditis elegans. P. pacificus is found on the Oriental beetle Exomala orientalis in Japan and the United States, whereas two common European species P. maupasi and P. entomophagus are predominantly found on cockchafers (Melolontha ssp.) and dung beetle (Geotrupes ssp.), respectively [2,4] These studies revealed an notable precision in the species-specificity between Pristionchus nematodes and beetles. Clade V encompasses C. elegans and other members of the suborder Rhabditina with the vertebrate-parasitic order Strongylida, the entomopathogenic genus Heterorhabditis and the order Diplogasterida The latter, which includes Pristionchus, is a sister group of some rhabditids [8]. They resemble each other in overall morphology, culture conditions, mode of reproduction and other features, i.e. they both feed on Escherichia coli bacteria under laboratory conditions and have a generation time of 3–4 days at 20°C They develop by lineage-dependant differentiation through a fixed number of cells and pass through four juvenile stages. The rare occurrence of spontaneous males of the XO genotype generated by X-chromosomal non-disjunction provides a way for outcrossing [10,11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
