Response of Treefrog Larvae to Drying Ponds: Comparing Temporary and Permanent Pond Breeders

Abstract

Most amphibian species with an aquatic larval stage use one of two types of breeding habitats: ephemeral or permanent water bodies. A common assumption is that, once a minimum developmental threshold has passed, tadpoles of species that use temporary ponds can respond adaptively to a drying larval habitat by hastening development to metamorphose before the pond dries. We investigated how different pond drying regimes affected the timing of metamorphosis and body size at metamorphosis of two closely related species of hylid treefrogs, one of which commonly breeds in temporary ponds (Hyla gratiosa) and the other in permanent ponds (Hyla cinerea). We experimentally manipulated the water level in cattle-tank communities, exposing tadpoles of each species to a slow drying treatment, a fast drying treatment, and a constant water level treatment. There was no direct effect of pond drying on the larval period or body size at metamorphosis of either species. The drying treatments indirectly affected these traits by increasing larval densities, which extended the larval period and produced smaller sizes at metamorphosis. The timing of metamorphosis and body size at metamorphosis of H. gratiosa were more plastic than the corresponding traits in H. cinerea, but this greater plasticity cannot be interpreted as adaptive. Our results emphasize the utility of the comparative approach in interpreting the potential adaptive responses of species to environmental variation.