Climate suggests environment‐dependent selection on lizard colour morphs

AIM: The maintenance of polymorphisms is often explained by sexual selection. However, natural selection may also constrain morphs to particular locations, causing geographical variation in morph diversity. In many well‐known polymorphic organisms in which the relevance of sexual selection on the maintenance of polymorphisms is widely supported, the role of environmental factors has been poorly studied. Here, we adopted a population‐level approach to assess the extent to which geographical variation in climate explains morph composition in a colour polymorphic lizard. We predict that rare morphs are more environmentally constrained than common morphs. LOCATION: Eastern Pyrenees, Western Europe. TAXON: Podarcis muralis (Lacertidae). The species shows up to five discrete colour morphs: white (W), orange (O), white‐orange (WO), yellow (Y) and yellow‐orange (YO). Populations strongly vary in morph composition. METHODS: We modelled the realised niche of each morph and the whole species with Maxent, Bioclim, and Domain, considering 110 localities over a relatively small but environmentally heterogeneous area. Morph ranges were compared to identify differences among their realised niches and local morph frequencies were interpolated to detect intra‐morph geographical variations beyond the mere presence of morphs. RESULTS: Differences between morph distributions were mainly associated to temperature seasonality and annual precipitation. While W, O, and WO morphs were found along the whole environmental range of the species, Y and YO morphs were restricted to a subset of the environmental conditions suitable for the species, namely high temperature seasonality and relatively high precipitation. Local frequencies of common morphs also differ among localities, the W morph being more frequent at lower altitudes than the O and WO morphs, which are more locally abundant at higher altitudes. MAIN CONCLUSIONS: We found a remarkable geographical relationship between climate and local morph composition that suggests environmentally dependent selection acting in a different way on common and rare morphs, most likely in interaction with sexual selection.