Sexual compatibility between two heterochronic morphs in the Alpine newt

Numerous populations of newts and salamanders are dimorphic: while some larvae become mature and thus paedomorphic, others metamorphose and become adult later. The two morphs largely differ in morphology. According to sexual selection theories, we could expect some female choice towards the alternative morphs. Although paedomorphosis can be adaptive in allowing resource partitioning and an earlier age at maturity, it is worth to determine the strength of sexual isolation between morphs. Indeed, whereas sexual compatibility may promote maintenance of polymorphism by mixing genes, sexual isolation could be the first step to sympatric speciation.
We staged more than 200 encounters involving the four possible crosses within and between the heterochronic morphs of the Alpine newt, Triturus alpestris (Amphibia, Caudata). We took into account both quantitative and qualitative aspects of behaviours, with particular emphasis on the success of sperm transfer. We also determined secondary sexual characters.
The success of heterotypic and homotypic encounters was similar, involving then sexual compatibility between the two heterochronic morphs. Paedomorphs and metamorphs displayed identical behavioural patterns at similar frequencies. Females did not appear to be selective against males on the basis of their epigamic characters.
Our results do not support hypotheses predicting sympatric speciation from polymorphic species. On the other hand, they are in favour of the models predicting maintenance of polymorphism