SSRP Abstract

Board 27: Sperm Competition in Dusky Salamanders

Student Scientist: Maya Moore ’24
Research Mentor: Sarah Woodley (Department of Biological Sciences, Bayer School of Natural & Environmental Sciences, Duquesne University)

Sperm competition is a reproductive phenomenon common in species where females mate with multiple males during a breeding season. This study used vertebrate models, Allegheny Mountain Dusky salamanders, to study what factors may cause a male to alter his sperm. In one experiment, we exposed males to chemical cues from rival males, and in a second experiment, we exposed males to higher levels of testosterone. By examining sperm, we can better understand fertility for conservation efforts and for humans as well.

Sperm competition, a form of sexual selection, occurs when males compete for fertilizations after copulation. Sperm competition is common in species where females mate multiple times, and males may invest differently in sperm number and seminal factors. I studied sperm competition in salamanders (Desmognathus ochrophaeus), where females mate with multiple males and store sperm internally until fertilization, which may occur months later. Males transfer sperm to females using a spermatophore. We hypothesized that males make larger spermatophores in the presence of rival male pheromones. Each male mated with the same female twice: once with a substrate saturated with rival male pheromones and once with a control substrate. There was no effect of rival male cues on spermatophore size. The time since last mating had a greater effect on spermatophore size, perhaps because spermatophores are energetically costly to produce. We also tested whether testosterone affects spermatophore size. We applied transdermal testosterone and an oil control to males and found that they produce larger spermatophores when exposed to higher levels of testosterone. We are extracting DNA from the spermatophore to estimate sperm number as well as protein content. Because salamanders are vertebrates, these data may be used to further understand fertility issues in humans as well as for species conservation efforts. Funded by NSF-REU Site Award 1757555.