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 shaped 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 expansion affected the geographic patterns of phenotypic variation in the Tyrrhenian tree frog Hyla sarda.

Location: Sardinia and Corsica Islands.

Taxon: Amphibia.

Methods: We collected tree frogs from four distinct geographic areas along the past expansion route, controlling for variation in altitude, local habitat effects, population demographic factors, and bioclimatic differences, allowing us to minimise confounding effects on the phenotypic trait studied.  Then, we scored intraspecific variation in two personality traits, two performance traits, and 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 sizes, longer limbs, and wider head sizes and displayed stronger take-off and adhesion performances than individuals from the source area in Sardinia.

Main Conclusion: 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 trait 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. Future studies should investigate the genomic architecture underlying the phenotypic patterns that emerged and explore the potential role of trait selection via spatial sorting and plasticity-led evolution in shaping these patterns.