Mating costs and gametic barriers to reproduction

Mating is essential to many organisms for their continued existence, and yet mating is costly. However, the fitness costs–which may immediately affect the individuals involved, or may affect their future reproductive output, are not often quantified. I assess costs that are acquired at different periods of the mating process–in search of a mate and gametic interactions after copulation. I first quantify the cost of mate searching of a monogynous spider measured by male longevity and I additionally examine how mate searching affects subsequent mating behaviours and performance. I find evidence for behavioural plasticity in males influenced by mate search duration to maximize female egg laying which may be mediated by male seminal fluids and/or female cryptic choice. I then use transparent organisms, Caenorhabditis nematodes, to identify a novel form of gametic isolation using 10 different species. This sperm mediated form of gametic isolation likely evolved from intra-species sperm competition, resulting in incompatibilities as a byproduct of competitive sperm in inter-species matings that caused early death, sterility, and invasive sperm. I further explored sperm-mediated gametic isolation in Caenorhabditis from the perspective of inter-species interactions by experimentally evolving populations with mixed species for six generations to show reproductive interference at the population level. Finally, I screened 25 genetic mutants and phenotyped 99 nearly isogenic lines of Caenorhabditis to identify genetic contributions to gametic isolation (i.e. speciation genes). I identified candidate genes that fall into two categories of phenotypic defects: ovulation defects increase the incidence of sperm invasion, whereas sperm signaling defects reduce the incidence of sperm invasion. These findings and novel methods add to our understanding of how costly mating can be, and how gametic interactions, in particular, contribute to reproductive isolation in Caenorhabditis.Ph.D