Date of Award
Master of Science (MS)
Sarah E. Hall
C. elegans, Mixed Mating, Pheromone, RNAi, Self-fertilization, TGF- β
Mating strategies, whether sexual or asexual, confer unique costs and benefits to populations and species that facilitate evolutionary processes. In wild isolates of Caenorhabditis elegans, mating strategies are dependent on developmental history. Outcrossing levels significantly increase when both hermaphrodites and males have transiently passed through the stress-resistant dauer diapause stage (postdauers). However, the molecular mechanisms of how life history can alter mating strategies have not been systematically explored. Mating behaviors of C. elegans can be attributed, in part, to sex-specific responses to ascaroside pheromone components. For example, high concentrations of the pheromone ascr#3 results in a strong avoidance response in hermaphrodites, but a slight attraction in males. We have demonstrated previously that postdauer hermaphrodites exhibit a decreased avoidance of ascr#3, which is the result of the downregulation of the osm-9 TRPV channel gene in postdauer ADL neurons. Thus, we hypothesized that sex-specific altered detection and/or response to pheromone components in postdauer animals could contribute to their increased outcrossing phenotype.
To test this hypothesis, we conducted mating assays using N2 Bristol and strains carrying mutations in daf-3/SMAD and mut-16/Mutator genes, which are required for the downregulation of osm-9 in postdauer hermaphrodite ADL neurons. First, we determined that the outcrossing level of N2 Bristol is primarily correlated with the developmental history of males, with a smaller effect due to hermaphrodites. Interestingly, postdauer males did not downregulate osm-9 in their ADL neurons, but instead exhibited an increased ability to detect mates via pheromone compared to control males. Additionally, daf-3 mutants exhibited loss of the increased outcrossing
phenotype in postdauers, illustrating the requirement of the TGF-β pathway in both males and hermaphrodites for this phenotype. Furthermore, the mut-16 strain exhibited negligible outcrossing, and attempts to rescue the outcrossing phenotype resulted in sterility due to gross morphological defects in the germline. Together, our results suggest a model whereby mating strategy is under combinatorial control of TGF-β and RNAi pathways.
Al-Saadi, Rose, "Genetic Determinants of Increased Outcrossing in Caenorhabditis elegans Following Dauer Diapause" (2020). Theses - ALL. 422.