Climate suggests environment‐dependent selection on lizard colour morphs

Abstract

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

Trait differences among discrete morphs of a color polymorphic lizard,Podarcis erhardii

“…Most importantly, all of these lizard species share a similar color polymorphism presented as distinct color badges on the throat, suggesting a similar evolutionary origin and function (Stuart-Fox & Ord, 2004). Color polymorphism is common among lacertid lizards, and the lacertid genus Podarcis is highly color polymorphic (Sacchi et al, 2007;Huyghe et al, 2007;Runemark et al, 2010;Pérez i de Lanuza, Sillero & Carretero, 2018). Previous studies of color polymorphic Podarcis species have identified color morph differences in size and survival (Calsbeek, Hasselquist & Clobert, 2010), ability to win staged contests (Huyghe et al, 2012;Abalos et al, 2016), absolute maximum bite force capacity and head muscle mass (Huyghe et al, 2008), and circulating hormone levels associated with aggressive behaviors (Huyghe et al, 2009a;Huyghe et al, 2009b).…”

“…Further, social interactions among morphs can dictate morph diversity across populations ( Pérez i de Lanuza, Carretero & Font, 2017 ). Thus, the number of morphs and the maintenance of color polymorphism can be the result of natural selection, sexual selection, both natural and sexual selection, and sometimes perhaps even neutral processes ( Gray & McKinnon, 2007 ; Rudh, Rogell & Höglund, 2007 ; Runemark et al, 2010 ; Pérez i de Lanuza, Sillero & Carretero, 2018 ). But across taxa, one thing remains clear: the key to understanding color polymorphism lies in identifying the number of morphs and morph-correlated characteristics and the broader context in which these alternative phenotypes are operating and interacting with each other.…”

Colour variation between different lineages of a colour polymorphic lizard

“…Most available results agree with the hypothesis that sexual selection is important for the maintenance of this polymorphism (Galeotti et al ., ; Pérez i de Lanuza et al ., , , ; Ábalos et al ., ). However, evidence from geographic variation of local morph composition and habitat use by morphs in sympatry suggests that this polymorphism is also environmentally constrained (Pérez i de Lanuza & Carretero, ; Pérez i de Lanuza et al ., ,b).…”

“…Colour polymorphism is common among lacertids, some species being currently under intense scrutiny with the aim to test hypotheses for the evolution of polymorphisms (e.g. Carretero et al ., ; Huyghe et al ., , ; Galeotti et al ., ; Pérez i de Lanuza, Font & Carazo, ; San‐José et al ., ; Pérez i de Lanuza, Font & Carretero, ; Pérez i de Lanuza, Carretero & Font, ; Pérez i de Lanuza, Sillero & Carretero, ). A crucial question to properly address the study of colour polymorphisms is whether relevant observers of the polymorphism (i.e.…”

“…Efforts have mainly focused on testing the assumption that ventral colour morphs may be linked to some sort of alternative reproductive strategies, but results are far from conclusive (Sacchi et al ., ; Calsbeek, Hasselquist & Clobert, ; Galeotti et al ., ; Scali et al ., ; Pérez i de Lanuza & Font, ; Ábalos et al ., ). The available evidence suggests that several selective forces may interact in the maintenance of this polymorphism, probably in a complex balancing selection scenario (Pérez i de Lanuza et al ., , ). Most available results agree with the hypothesis that sexual selection is important for the maintenance of this polymorphism (Galeotti et al ., ; Pérez i de Lanuza et al ., , , ; Ábalos et al ., ).…”