Abstract
Environmental pollution can affect the sex ratio in naturally occurring populations of some species. Amphibians are a highly at-risk taxon and are experiencing worldwide decline, and their sex ratios in breeding aggregations can be altered by environmental pollution. In this study, we examined how the reproductive behavior of wood frogs (Rana sylvatica), a widespread North American amphibian, is influenced by the sex ratio in their environment in order to identify if environmental pollution has an indirect effect on reproductive behavior. We hypothesized that the higher the sex ratio of wood frogs (the ratio of males to females), the more often female wood frogs would exhibit social avoidance behavior (i.e., time spent underwater) and experience male harassment (mating grasp attempts by males that, in excess, can be lethal to females).

Using field arenas (wading pools) on the edge of a natural vernal pond, we manipulated the sex ratio of wood frog “populations” within the arenas in three treatments (1 male : 1 female; 4 males : 1 female; 7 males : 1 female). We quantified female wood frog social avoidance behaviors and evidence of male harassment by reviewing videos of the field trials. Our results indicate that there were no significant differences between female avoidance behavior across treatments. However, we did identify increased male harassment in some treatments: the higher the sex ratio, the more frequently females experienced harassment. Our results suggest that pollution-induced sex ratio skew may also alter the risk that females experience in natural breeding aggregations.