BackgroundThe free-living nematodeDiploscapter coronatusis the closest known relative ofC. eleganswith parthenogenetic reproduction. It shows several developmental idiosyncracies, for example concerning the control of meiosis and embryonic axis formation [1]. Our recent genome analysis [2] provided some support for the view thatD. coronatusis a product of interspecies hybridization. Here we present additional data towards this assumption. Based on genomic and transcriptomic data we try to better understand the molecular basis of developmental idiosyncrasies in this species in an evolutionary context by comparison with selected other nematodes.ResultsIn a genomic comparison betweenD. coronatus,C. elegans, other representatives of the genusCaenorhabditisand the more distantly relatedPristionchus pacificusandPanagrellus redivivus, certain genes required for normal embryogenesis inC. eleganswere found to be restricted to the genusCaenorhabditis.The mRNA content of earlyD. coronatusembryos was sequenced and compared with similar stages inC. elegansandAscaris suum.We identified 350 gene families transcribed in the early embryo ofD. coronatusbut not in the other two nematodes. Looking at individual genes transcribed early inD. coronatusbut not inC. elegansandA. suumwe found that orthologs of most of these are present in the genomes of the latter species as well, suggesting heterochronic shifts with respect to expression behavior. Considerable divergence between alleles lends further support to the view thatD. coronatusmay be the result of an interspecies hybridization. Expression analysis of early acting single copy genes yield no indication for silencing of one parental genome.ConclusionsOur comparative cellular and molecular studies support the view that the genusCaenorhabditisdiffers considerably from the other studied nematodes in its control of development and reproduction. The easy-to-culture parthenogeneticD. coronatus, with its high quality draft genome and only a single chromosome when haploid, offers many new starting points on the cellular, molecular, and genomic level to better understand alternative routes of nematode development and reproduction.
