Feeding specialization in heterochronic newts (Triturus alpestris, Amphibia, Caudata)

Abstract

Polymorphisms are suspected to reduce competition among conspecifics in heterogeneous environments by allowing differential resource use. However, the adaptive significance of alternative morphs has been poorly documented. The aim of this study was to test this hypothesis by comparing diets of syntopic heterochronic morphs (paedomorphs and metamorphs) in the Alpine newt, Triturus alpestris in three European alpine lakes. Feeding performance was also tested in the laboratory. The two morphs differ in the functional morphology of their feeding apparatus. Only paedomorphs are able to expel water behind the mouth during prey suction through gill slits. We observed a substantial trophic differentiation between morphs consistently in all lakes. Paedomorphs primarily preyed on plankton whereas metamorphs foraged on terrestrial invertebrates that fell to the water surface. Laboratory observations were consistent with field patterns. In paedomorphs, prey capture success rate was better than in metamorphs when foraging on aquatic crustaceans, but was less successful when foraging on terrestrial invertebrates caught at the water surface. By reducing competition, resource partitioning contributes to the coexistence of the alternative morphs in lakes devoid of vertebrate competitors and predators. Food diversity is thus an important factor favoring the evolutionary maintenance of facultative paedomorphosis in natural populations