Origins of Self-Fertility in Three Caenorhabditis Nematodes

How does novelty arise during evolution? Over the past few decades, work from many labs has developed a detailed genetic and cellular picture of how nematode mating systems were altered to yield self-fertile hermaphrodites from ancestral females. Since most analyses involve Caenorhabditis, this review focuses on three androdiecious species from this genus. In each, male spermatogenesis and sperm activation programs were co-opted for use in XX animals. Since each species followed a unique pathway to self-fertility, comparative analyses reveal how these regulatory pathways changed to produce new traits. Moreover, ecological studies are beginning to provide models for how selection and population structure might have interacted with these regulatory changes through a stepwise process. Taken together, our new understanding of how this complex trait originated combines evolutionary, genetic and developmental principles into a robust picture of evolutionary change. Comparing these results from Caenorhabditis with studies of more distant groups of nematodes provides further support for many of the conclusions.