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.
K E Y W O R D Scolour polymorphism, ecological niche