Spatial differentiation of background matching strategies along a Late Pleistocene range expansion route
Late Pleistocene climate changes have deeply impacted the range dynamics of temperate species. While the genetic legacy of these dynamics has been widely investigated, little is known about their phenotypic consequences. Anti-predatory strategies offer intriguing opportunities to study phenotypic evolution in response to dispersal dynamics since the ability to avoid predation can be pivotal for populations colonizing new environments. Here we investigated the spatial differentiation of background colour matching strategies along a Late Pleistocene range expansion route of a temperate species, the Tyrrhenian tree frog Hyla sarda. Using common-garden experiments, we investigated whether individuals sampled in the source area (Sardinia) and individuals sampled in the newly founded area (Corsica) differ in two components of the camouflage strategy: colour change abilities and background choice behaviour. We found a remarkable spatial structure in both colour change abilities and background choice behaviour, across the expansion range. Tree frogs from the source area displayed higher colour change abilities and a more pronounced preference for a greener background, with respect to tree frogs from the newly colonized area. We discuss these results in the context of the spatial and demographic components of the expansion dynamics. Our results support the intriguing hypothesis that Late Pleistocene biogeographic history might be an overlooked major player in shaping current spatial patterns of phenotypic traits variation across animal populations.