The emergence of self-fertility in Caenorhabditis is ideal for investigating the origin of new traits, since it evolved recently in three separate lineages. In each case, the self-fertile hermaphrodites are XX animals that gained the ability to make sperm during larval development, but still produce oocytes during adulthood. The sex-determination pathway controls spermatogenesis and oogenesis, so it must have been modified to create hermaphrodites. Characterizing the sex-determination pathway in the male/female species C. nigoni, which represents the ancestral state of the genus, will help us identify the genetic modifications that cause spermatogenesis in XX hermaphrodites of its sister species C. briggsae. Characterizing these modifications is essential for defining the changes needed to produce self-fertility. Using a reverse genetic approach, I generated C. nigoni mutations in critical sex-determining genes, along with recessive visible mutations to use as balancers. Genomic edits were made by injecting gravid C. nigoni females with Cas9 RNPs. C. nigoni
tra-1(
v481) masculinizes the somatic tissues of putative XX animals. Moreover, it appears to arrest gonad development and these
Cni-tra-1(
v481) XX animals are unable to sire progeny. TRA-1 is known to control gonad development in C. elegans, but phenotypes like ours have not been described. More recently, I generated the alleles
Cni-tra-2(
v498) and
Cni-fem-3(
v496), and balanced them with
Cni-unc-104(
v494) and
Cni-unc-129(
v495), respectively. More detailed analyses are ongoing; however, diminished brood sizes and reduced mating efficiency seen within isolate JU1422 have made the characterization of these mutants slow-going. The sister species, C. briggsae and C. nigoni, can form fertile female hybrids. To determine what C. nigoni genes are responsible for the dominant feminization that has been observed in these hybrids, I will use my new sex-determination mutants to make heterozygous hybrids for each gene. Identifying which genes are responsible for repressing XX spermatogenesis in these animals could indicate which genes have key differences between these sister species, differences that might be critical for the origin of self-fertility. These comparative studies should lead to interesting hypotheses about which genes were critical for the evolution of self-fertility in C. briggsae. Using gene editing, we can swap any genes of interest between the two sister species. A definitive test would be to swap one of these genes into C. nigoni and observe its effect, it may be possible to drive self-fertility in a male/female species this way.