A Comparative Study of Feminine Reproduction in a Rhabditis Clade

Here I studied the reproductive strategies of nematodes in a Rhabditis clade. The identified members of this clade include Rhabditella axei and the Rhabditis species R. sp. SB347, R. sp. SB372, R. sp. JU1782, R. sp. JU1783, and R. sp. JU1809. To better define the reproductive strategies of the hermaphrodites/females within this clade the morphology of the gonad as well as other elements of reproductive strategies were compared, with the well-studied Caenorhabditis elegans hermaphrodite reproductive strategy used as a standard. It was found that the reproductive strategies of hermaphrodites/females of the Rhabditis clade differ from that of C. elegans hermaphrodites in a number of ways. In at least one, if not more, species within this clade, clear differences were documented in distal gonad morphology, the proportion of mitotically dividing cells in the distal gonad, chromosome morphology, the size of the nucleoli, spermatheca morphology, and offspring sex-ratios. However, a number of similarities were found as well. C. elegans, R. axei, and SB372 gonads have comparable numbers of mitotically dividing cells. In C. elegans, R. axei, and SB347 meiosis resumes in the most proximal oocyte. Furthermore, C. elegans, SB347, and SB372 hermaphrodites all produce broods of a similar size. Lastly, the hermaphrodites/females of all species examined had didelphic gonads containing oocytes in the proximal region, and these gonads occupied a large portion of the total worm volume in all species. In the future, these findings will be combined with molecular phylogenetic studies to examine the evolution of diverse reproductive strategies within closely related nematode species. Importantly, the reproductive features of one or more of the trioecious species within this clade suggests that it could be an excellent model organism for the study of parasitic nematodes. Moreover, comparative studies within the Rhabditis clade provide an informative parallel to comparative studies within the genus Caenorhabditis