Interpopulation Variability in Evasive Behavior in the Oregon Spotted Frog (Rana pretiosa)

Abstract

Few data exist that quantify evasive behavior in postmetamorphic anurans. On the basis of our casual observations that Oregon Spotted Frogs (Rana pretiosa) from one of two different populations appeared to exhibit a more pronounced evasive response, we used a pseudopredator stimulus to quantify the evasive response of juveniles from the two populations. We drew test animals from a pool of animals for each population that were captive-reared under identical conditions. Using latency to initial response, we compared the distribution of response times between the two populations at two sequential intervals over the rearing period. In both experiments, the Conboy Lake population had shorter latency-to-response times than the Black River population. However, we also found that latency-to-response times were shorter during the second test interval than during the first test interval for each population. The basis of population differences in response times may reside in differences in the predator set influencing each population, contaminants differentially influencing the Black River population in a negative manner, or some combination of both. Explanation for the faster latency-to-response times in the second experiment is unclear since both maturation and the length of the captive rearing interval may contribute to the effect, but they are confounded in this study.