Local environmental conditions affecting anuran tadpoles’ microhabitat choice and morphological adaptation

Abstract

In this study, we investigated the environmental variables that best explained tadpole occurrence, as well as associations between environmental variables and the morphological traits of tadpoles. We modelled the occurrence of tadpoles to evaluate the significance of trait–environment relationships by sampling in 86 ponds, measuring a set of environmental descriptors of these ponds, determining the tadpoles’ external-morphology changes and using a generalised linear mixed model approach. The best fitting model predicting tadpole occurrence included all the environmental variables measured (pond dimensions, pond margin type, pond bottom substrate, vegetation type inside the pond, vegetation type in the pond margins, landscape descriptors) and seven morphology–environment interactions. Tadpoles are capable of fine-tuning their morphology according to the environmental traits of the pond and land use changes around the pond. Vegetation heterogeneity of ponds interacts with tadpole morphology primarily on tail size and deviations in the mean position of the eye, nostril and mouth. Moreover, there are increases in body size and tail length in smaller ponds, as well as in ponds surrounded vegetation changes from forest to pasture or short crops. Changes in environmental variables as a result of land use change can affect the dispersion of adult frogs and, consequently, the occurrence of and morphological variations in tadpoles. Local environmental variables play important roles driving tadpoles’ microhabitat choice; once tadpoles cannot select the site of their developmental, they need to compensate for any mismatching by induced morphological adaptations.