Female treefrog preference for breeding sites matches offspring performance in the presence of two anuran competitors.

Preference-performance theory predicts that females should select breeding sites that maximize offspring performance. Amphibians have been a model system for investigating habitat selection, yet most studies have focused on habitat selection in response to predators and conspecifics. We investigated female oviposition site selection and larval performance in eastern gray treefrogs (Hyla versicolor) among pools with and without one of two ecologically distinct heterospecific larvae, the green frog (Rana clamitans) and the American bullfrog (Rana catesbeiana). Pools without heterospecifics were used on more nights and had more eggs deposited compared to pools with heterospecifics. In a competition experiment, treefrog larval performance matched this female preference: tadpoles developed faster and grew larger in the absence of either heterospecific. Although we hypothesized that bullfrogs would more strongly affect female treefrog preference and offspring performance because of previous work demonstrating that bullfrogs had stronger negative effects on other tadpoles, both heterospecifics elicited similar responses. The effects of heterospecifics on anuran breeding site selection are understudied and not well understood, and our results demonstrate that female selection of breeding sites is an adaptive behavior for offspring in the presence of heterospecific competitors.

Joint toxicity of chlorpyrifos and endosulfan to Pacific treefrog (Pseudacris regilla) tadpoles.

Recent ecotoxicology studies have focused on the potential interaction of pesticides and the effects these interactions may have on aquatic ecosystems. We examined the combined effects of two insecticides, endosulfan and chlorpyrifos, that have been previously examined individually on survival, growth, and development of Pacific treefrog (Pseudacris regilla) tadpoles. Historically, both pesticides have been heavily used in the Central Valley of California, been identified in downwind montane areas, and are highly toxic to amphibian larvae. Tadpoles were exposed to chlorpyrifos and endosulfan individually and in combination from Gosner stage 25 through metamorphosis to evaluate the individual effects and the interaction between these insecticides. Chlorpyrifos alone did not affect survival or body size after 30 days, even at concentrations greater than the previously reported LC50. Survival and body size decreased with increasing endosulfan concentrations. The interactive effects of the insecticides depended on concentration and exposure duration. In combination, 137 µg/L chlorpyrifos inhibited the negative effects of endosulfan on growth and survival. The presence of both insecticides in combination facilitated the development of axial malformations. In the presence of endosulfan with either 266 or 394 µg/L chlorpyrifos, malformations occurred in 33 and 87 % of tadpoles, respectively. Our results indicate that organophosphorus and organochlorine pesticides with different modes of action can result in varying interactions depending on their concentrations and on the end points being assessed. Further examination of contaminant impacts on natural aquatic systems should continue to focus on the effects of multiple contaminants and their potential for unpredictable, nonadditive interactions.