Female chorus frogs delay mate choice under suboptimal environmental conditions

Many traits important for reproductive isolation are environmentally responsive. However, most studies examining reproductive isolation do not explicitly take into consideration environmental variation. Temperature can have a particularly large effect on reproductive behaviors, especially in ectotherms. Here, we tested whether temperature affects the degree of reproductive isolation between the Upland chorus frog (Pseudacris feriarum) and its congener P. nigrita. These two species engage in costly hybridization in nature, leading to reinforcement of male signals and female preferences in sympatry. However, male advertisement calls vary with temperature such that the difference between the advertisement calls of the two species is narrower at cold than at warm temperatures. To examine the effect of temperature on reproductive isolation in this system, we performed six binary choice preference trials using sympatric female P. feriarum. In these experiments, we acclimated females to either warm (20°C) or cool (10°C) temperatures and gave them a choice between heterospecific and conspecific advertisement calls appropriate for the temperature. We also conducted experiments where we gave females a choice between more similar stimuli at warm temperatures to test whether females have more specific preferences at cold temperatures. We found that females always preferred the conspecific advertisement call, though they tended to make more mistakes when given a choice between more similar stimuli at warm temperatures. However, females took twice as long to make a choice in sub-optimal conditions. This time delay may lead to increased risk of hybridization, despite female ability to discriminate between calls. Our results highlight the importance of considering environmental context when examining traits involved in reproductive isolation.