Evolutionary history drives the geographical distribution of dorsal patterns in the common wall lizard (Podarcis muralis)

Abstract

Melanin-based dorsal pattern polymorphisms are common in reptiles and generally evolve under the interaction between opposite selective pressures, notably thermal advantage in cold environments and background matching to avoid predation. When those pressures change over space and time, the relative frequencies of morphs can vary across the species range. However, no previous study has analysed the spatial patterns of variation of morphs under a phylogenetic perspective in addition to the adaptive responses to natural selection. In this study, we focused on the distributional patterns of the three dorsal morphs of Podarcis muralis at wide-range scale to assess how they associate with geography, climate, microhabitat, phylogeny and sexual dimorphism. By using open access data from iNaturalist, we assembled a dataset of 4096 georeferenced points with information on sex and morph. Data were analysed through Bayesian GLMs, and four alternative models were formulated depending on the specific factors affecting morphs’ frequency. The dorsal morphs are not randomly distributed in Europe, but follow clear geographic patterns, vary with altitude and habitats, show sex-specific trends, and correlate with the phylogenetic history of the species. When comparing models, the phylogenetic model always obtained the best performance, and no overlap with other models occurred, thus best explaining the distributional patterns of dorsal morphs. The evolutionary processes, in addition to present environmental pressures, can significantly affect local-scale microevolutionary adaptations, influencing the current distribution of dorsal phenotypes across the species range. More generally, results point out the importance of considering the evolutionary processes when analysing distributional patterns of polymorphisms.