Drivers of phenotypic variation along a Late Pleistocene range expansion route

Abstract

Aim: Understanding how interindividual variation within populations drives the evolution of biodiversity patterns is a major challenge in ecology and evolutionary biology. By reshuffling species distribution in space and time, Pleistocene climatic oscillations contributed to mould the structure of biodiversity. While the genetic legacy left by these processes has been widely investigated, their effects on phenotypic diversity remain largely unexplored. Here, we investigated whether Pleistocene range expansions affected the geographic patterns of phenotypic variation in the Tyrrhenian tree frog Hyla sarda, an amphibian species which underwent a northward range expansion from Sardinia Island to Corsica Island during the Last Glacial Maximum.

Location: Sardinia and Corsica Islands.

Taxon: Amphibia.

Methods: We collected tree frogs from four geographic areas along the past expansion route, controlling for altitude, local habitat effects, demographic factors, and bioclimatic differences between geographic areas. Then, we scored intraspecific variation in two personality traits, two performance traits, along with morphological traits likely involved in the dispersal process.

Results: Tree frogs from Corsica were more prudent in a novel environment, they had significantly larger body size, longer limbs, wider head size, and displayed stronger take-off and adhesion performances compared to individuals from the source area in Sardinia.

Main Conclusion: Overall, these results suggest a non-random spatial sorting of the intraspecific variation in multiple phenotypic traits during the range expansion phase. In turn, they also suggest that population differentiation in phenotypic traits associations might be a legacy of past biogeographic dynamics, identifying an overlooked driver of current patterns of intraspecific variation in phenotypic integration and opening intriguing evolutionary scenarios on the processes shaping the phenotypic architecture of animal populations.