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

Unpredictable environments are expected to select for adaptive plasticity i n traits enabling adjustment of phenotype to prevailing environmental condi tions. Common frogs (Rana temporaria) breed frequently in ponds, which dry up before the aquatic larvae have metamorphosed, and consequently, plastici ty in timing of metamorphosis in response to pond drying could be adaptive. We investigated the responses of half- and full-sib R. temporaria larvae t o 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 hypot hesis, we found that larvae exposed to the decreasing water treatment metam orphosed significantly faster than their sibs in the constant water treatme nts. Furthermore, age and size at metamorphosis were positively correlated in the constant water treatments, but negatively correlated in the decreasi ng water treatment. However, larvae from decreasing water treatment metamor phosed, on average. at a smaller size as compared to larvae from the consta nt water treatments, even after controlling for variation in developmental time. Since smaller size at metamorphosis is likely to be related to reduce d fitness, this indicates that faster development may trade off with other components of fitness. The results further show that the amount of food rec eived during the four first days of development influenced age and size at metamorphosis, reinforcing the view that early life nutrition may have a si gnificant impact on later life fitness. Although there was a genetic compon ent to developmental rates, we found no evidence for genetic variation in p lasticity. In accordance with evidence from other studies, our results sugg est existence of adaptive phenotypic plasticity in amphibian development.