Adaptive phenotypic plasticity in timing of metamorphosis in the common frog Rana temporaria

Unpredictable environments are expected to select for adaptive plasticity in traits enabling adjustment of phenotype to prevailing environmental conditions. Common frogs (Rana temporaria) breed frequently in ponds, which dry up before the aquatic larvae have metamorphosed, and consequently, plasticity in timing of metamorphosis in response to pond drying could be adaptive. We investigated the responses of half- and full-sib R. temporaria larvae to simulated pond drying in a factorial experiment to test whether there is adaptive phenotypic plasticity in timing of metamorphosis, and whether this plasticity is genetically determined. As expected under the adaptive hypothesis, we found that larvae exposed to the decreasing water treatment metamorphosed significantly faster than their sibs in the constant water treatments. Furthermore, age and size at metamorphosis were positively correlated in the constant water treatments, but negatively correlated in the decreasing water treatment. However, larvae from decreasing water treatment metamorphosed, on average. at a smaller size as compared to larvae from the constant water treatments, even after controlling for variation in developmental time. Since smaller size at metamorphosis is likely to be related to reduced fitness, this indicates that faster development may trade off with other components of fitness. The results further show that the amount of food received during the four first days of development influenced age and size at metamorphosis, reinforcing the view that early life nutrition may have a significant impact on later life fitness. Although there was a genetic component to developmental rates, we found no evidence for genetic variation in plasticity. In accordance with evidence from other studies, our results suggest existence of adaptive phenotypic plasticity in amphibian development.