Partial divergence in microhabitat use suggests environmental-dependent selection on a colour polymorphic lizard
The study of polymorphic organisms in which sexual selection strongly drives the maintenance of the polymorphism often ignores the environmental context. However, natural selection is also crucial, often interacting with sexual selection. While most evidence suggests that sexual selection underlies the maintenance of the colour polymorphism shown by the common wall lizard, Podarcis muralis, involving up to five sympatric morphs (white -W-, yellow -Y-, orange -O-, white-orange -WO- and yellow-orange -YO), recent results using realised niche models suggest morph distribution at a geographical scale is constrained by climate. The Y and YO morphs occupy a narrow space within the niche of the other morphs, and local frequencies of W, WO and O morphs are environmentally dependent, with O and WO showing higher local frequencies in the most humid habitats. We hypothesised that morphs may behaviourally compensate for these differences at a microhabitat scale. Here, we tested this hypothesis collecting field microhabitat data from representative natural populations. Results highlighted that O lizards are partially segregated in microhabitat relative to the other morphs, tending to occupy more humid (vegetated, close to water) sites, and suggesting a physiological constraint. In contrast, the other morphs do not differ in microhabitat use, suggesting that the ecological restriction of Y and YO morphs derives from an indirect relationship between climate and population parameters (sex ratio, density) crucial for social selection, eventually involving alternative behavioural strategies.
The maintenance of different colour phenotypes (morphs) in a single population occurs in complex evolutionary scenarios where several selective forces interact. Common wall lizards may be white, orange, yellow, white-orange or yellow-orange ventrally. This polymorphism is most likely driven by sexual selection, but climate probably constraints the environmental distribution of morphs, driving local morph diversity. Here, we explore if geographical differences in morph distribution result in microhabitat segregation. Our results show that orange lizards appear more frequently in humid habitats than the other morphs, suggesting a direct relationship between ecophysiology and habitat use. Although yellow and yellow-orange morphs present a narrow distribution at a geographical scale, they do not differ from the white and white-orange morphs in microhabitat, suggesting that their restricted distribution is indirectly caused by some source of environmental dependence on social selection instead of a direct physiological constraint.
KeywordsColour polymorphism Ecology Environmental-dependent selection Microhabitat Podarcis muralis
We are grateful to D. Klomp for comments on an earlier version of this manuscript. We also thank the editor and two anonymous reviewers for their valuable comments.
GPL was supported by post-doctoral grant (SFRH/BPD/94582/2013) from FCT under the Programa Operacional Potencial Humano – Quadro de Referência Estratégico Nacional funded by the European Social Fund and Portuguese Ministério da Educação e Ciência. MAC is supported by project NORTE-01-0145-FEDER-000007. The study was supported by FEDER through the COMPETE program (ref. 008929) and Portuguese national funds through the FCT (Fundação para a Ciência e a Tecnologia, Portugal) project PTDC/BIA-BEC/101256/2008, the FCT project 30288 02/SAICT/2017 (Projetos de Desenvolvimento e Implementação de Infraestruturas de Investigação, RNIE - Programa Operacional Regional do Norte - Portugal 2020), and a grant (CGL2011-23751) from the Spanish Ministerio de Ciencia e Innovación.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Binocular observations allowed minimising lizard disturbance (at worst, lizards avoided the observer by moving away). No lizards were captured or manipulated during the observations. The habitat was not altered in any way. This research complied with the ASAB/ABS Guidelines for the Use of Animals in Research. Permits for working in our study area were provided by the Préfecture des Pyrénées Orientales (Arrêté no. 2016-2-09).
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