Egg development in parthenogenetic nematodes: variations in meiosis and axis formation.

In the well studied model nematode Caenorhabditis elegans entrance of the sperm induces an anterior-posterior polarity in the egg and determines the orientation of the primary embryonic axis. Subsequently, fusion of two haploid gamete nuclei results in a diploid zygote as a prerequisite for normal embryogenesis. Here we analyze the establishment of embryonic polarity and diploidy in the absence of sperm in three parthenogenetic nematode species from three different families, Diploscapter coronatus (Diploscapteridae), Acrobeloides nanus (Cephalobidae) and Plectus sp. (Plectidae). We find that they not only differ from C. elegans in these two aspects but also from each other, indicating variant solutions for the same developmental challenges and supporting the view that the parthenogenetic mode of reproduction has been acquired multiple times independently.