Sexual compatibility between two heterochronic morphs in the Alpine newt, Triturus alpestris

Paedomorphosis, in which individuals retain ancestral characteristics in th e adult stage, is widespread in newts and salamanders and is suspected to p lay an important role in evolution. In some species, paedomorphosis is facu ltative with some individuals forgoing metamorphosis. Optimality models hav e been proposed to explain the maintenance of this polymorphism, but requir e the integration of reproductive patterns into the models. We investigated the frequencies of inbreeding and outbreeding in two syntopic heterochroni c morphs of the Alpine newt. The two morphs are sexually compatible: encoun ters between and within morphs were equally successful in terms of spermato phore transfer. Behavioural observations were in agreement with the sexual compatibility observed. Nevertheless, paedomorphic males displayed to femal es less frequently than metamorphic males. The two morphs differ largely on the basis of sexual secondary characteristics, but the majority of these t raits did not affect mating success. Because of the large flow of genes bet ween the two heterochronic morphs and because of the absence of spatial and temporal isolation, these results do not support sympatric speciation mode ls, but are in favour of the maintenance of polymorphism in natural populat ions. (C) 2001 The Association for the Study of Animal Behaviour.