Phenotypic variation in Xenopus laevis tadpoles from contrasting rainfall regimes is the result of adaptation and plasticity

Phenotypic variations between populations often correlate with climatic variables. Assessing the adaptation of a species' populations from differing environments over a large spatial scale can provide insight into the mechanisms such as local adaptation and phenotypic plasticity that can result in a species persistence in heterogeneous environments. Amphibians, and especially their larvae, are good models for studies of phenotypic variation as they are especially sensitive to the immediate environment. Few studies have attempted to determine the mechanisms that drive phenotypic variation among populations over a large spatial scale in amphibians especially across contrasting climatic regimes. The African clawed frog, Xenopus laevis, occurs in two regions with contrasting rainfall regimes in southern Africa. We hypothesise that the phenotypic variation of life history traits of X. laevis tadpoles from these regions is a result of a combination of plastic and adaptive responses. We measured larval life history traits such as size development, time to metamorphosis and survival variation in a reciprocal exchange experiment using outdoor mesocosms. Supporting our prediction, we found that the measured variation of all traits was explained by both adaptation and plasticity. However, the reaction norms differed between populations suggesting adaptive plasticity. The phenotypic response to translocation, additionally, came at a cost, as survival was significantly lower when tadpoles were translocated rather than reared in their environment of origin. Our study demonstrates that there is both a genetic and non-genetic basis for phenotypic differences in amphibian larvae, which can explain the persistence across two contrasting rainfall regimes.