Local Adaptation or Environmental Induction? Causes of Population Differentiation in Alpine Amphibians

Many amphibian species have wide altitudinal and latitudinal distribution ranges, and hence, different populations of the same species may face very different environmental constraints and selection pressures. Although the potential differences in selective regimes along altitudinal and latitudinal gradients are still largely unknown, a number of studies have documented conspicuous phenotypic differentiation along these gradients. We reviewed the evidence for among population genetic differentiation (past adaptation) and within population genetic variation (potential for future adaptation) in different life history traits in amphibians, focusing mainly in studies conducted with the Common Frog, Rana temporaria, and with the Alpine Newt, Triturus alpestris. Except for larval traits, the evidence for genetic basis of population differentiation, as well as for heritability of different traits, is limited. This is especially true for traits expressed only in adults, such as age of maturity, fecundity and longevity, and traits relating to tolerance to different types of environmental stresses (e.g. nitrate, UV-B, pesticide tolerances). We suggest that due to the relative ease in which the genetic basis of most traits in amphibians can be studied, they might provide good model systems to study possible consequences of, and adaptation to, environmental changes expected to occur in forthcoming decades.