Viviparity in Salamandra salamandra (Amphibia: Salamandridae): Adaptation or Exaptation?

Ovoviviparity and viviparity have been described as derived reproductive modes in urodeles. Moreover, several authors have suggested that viviparity represents an adaptive solution to the harshness of high-altitude environments. Populations of Salamandra salamandra display ovoviviparity and viviparity as polytypic and polymorphic reproductive modes. This variation enables a test of the classic adaptive hypothesis of viviparity from a microevolutionary perspective. Comparative analysis using Felsenstein's independent contrasts and phylogenetic autocorrelation methods in six populations of S. salamandra have shown non-significant associations between altitude of populations and viviparous traits. Although these preliminary results must be corroborated with the study of more populations, we suggest an internalist hypothesis that takes into account the ubiquitous production of unfertilized, nutrient eggs in viviparous females. Thus, viviparity might have evolved as a byproduct of intraoviductal competition for resources by developing larvae. In this context, an exaptive scenario rather than an adaptive scenario might explain the origin of viviparity in S. salamandra and other urodeles.