Date Published: March 15, 2019
Publisher: Public Library of Science
Author(s): Jesús Ortega, José Martín, Pierre-André Crochet, Pilar López, Jean Clobert, Emma Pomeroy.
Widespread species often show extensive phenotypic variation due to the contrasting abiotic and biotic factors that shape selective pressures in different environments. In this context, the gradual and predictable patterns of variation in climatic and environmental conditions found in mountain areas offer a great opportunity to explore intraspecific phenotypic variation. For instance, temperature is negatively correlated with altitude and virtually all aspects of the behavior and physiology of ectotherms are sensitive to body temperature. In this work, we tested the hypothesis that morphology, dorsal and ventral coloration and the chemical profile of femoral secretions show interpopulational and seasonal variation in the lacertid lizard (Podarcis liolepis). We compared lizards from three populations inhabiting lowland and highland habitats in the French Pyrenees that were closely related genetically. We found that highland lizards were larger, stockier, had longer heads and more femoral pores and had a darker dorsal coloration than lowland ones. In addition, we detected interpopulational differences in both the abundance and the richness of chemical compounds in the glandular secretions, and we also found seasonal variation in the overall chemical composition. Dorsal and ventral coloration differed seasonally and between populations. Ventral and dorsal brightness were higher in lowland than in highland lizards in the reproductive season whereas the reversed trend was found in the non-reproductive season but only for dorsal brightness. In addition, all lizards had browner dorsal coloration in the non-reproductive season, and lowland lizards were greener in the reproductive season. By integrating information from both visual and chemical systems, our works offers a comprehensive view of how these lizards communicate in a multimodal context.
Understanding patterns of geographical variation within species is of interest since the mechanisms may be similar to those responsible for divergence between species [1–3]. Abiotic variables can drive spatial and/or temporal variation in organismal traits [4–5] and populations of the same species inhabiting distinct localities can experience contrasting ecological and climatic conditions that, ultimately give rise to phenotypic divergence [6–7]. Hence, studying widespread species that occupy different environments and show extensive phenotypic variation has improved our understanding of the link between environmental and phenotypic variation [8–10]. Specifically, elevational differences found in mountain areas bring about gradual and predictable patterns of variation in climatic and environmental conditions on a small geographical scale, e.g. temperature decreases while humidity increases with elevation. In this context, the ecology of ectotherms, such as lizards, should be particularly affected by elevation because so much of their biology is temperature dependent [11–12]. Thus, lizards distributed over a wide elevational range may exhibit phenotypes, such as body size , body coloration , and visual  and chemical signal design , that are either the result of phenotypic plasticity and/or local adaptation, generating clines for several traits with elevation.
Our work showed that P. liolepis replicates the same pattern of morphological variation with elevation found in closely related species within the genus Podarcis, but not in other lizards. We also described temporal and spatial variation in lizard phenotypes. Dorsal and ventral coloration displayed seasonal and interpopulational variation. In addition, we found seasonal variation in the chemical composition of femoral secretions in a temperate continental lizard species and also demonstrated interpopulational variation in chemical profiles.
Overall, highland lizards were larger, more robust, had longer heads and more femoral pores and had a darker dorsal coloration than lowland ones. We also detected interpopulational and seasonal variation in femoral secretion composition, ventral, and dorsal coloration. There were strong differences in the abundance and richness of chemical compounds. Ventral and dorsal brightness were higher in lowland than in highland lizards in the reproductive season whereas the reversed trend was only found in the non-reproductive season for dorsal brightness. Lowland and the non-reproductive season lizards were redder than highland and the reproductive season ones, respectively. In addition, all lizards had browner dorsal coloration in the non-reproductive season, and lowland lizards were greener in the reproductive season. Hence, our results highlight that high phenotypic variation can even be present in closely related populations. Despite the logistic difficulties, we encourage future research on widespread taxa over different environmental conditions to disentangle the causes of intraspecific and seasonal variation in phenotypes.