Sexual dimorphism (SD) is a common trait in animals, appearing due to sexual selection, fecundity selection or natural selection promoting sexual niche segregation. To evaluate the relative contribution of these mechanisms in shaping phenotypic patterns, we explored morphological and functional SD in the Moorish gecko, Tarentola mauritanica (Linnaeus, 1758). This species is particularly interesting because the sex of individuals is determined by the incubation temperature of the eggs, which may pose constraints on the expression of SD. Our results indicate the existence of marked SD in T. mauritanica. Males were overall larger than females, and were able to bite harder, but we found no differences between the sexes in climbing capacities. When differences in body size were taken into account, SD became less pronounced, appearing only in relative head dimensions, relative hind limb length and bite force. Different body parts varied under the same static allometric slopes in both sexes, a pattern not very usual in lizards. Put together, our results suggest constraints in the expression of SD in the Moorish gecko, possibly due to either not particularly intense sexual selection, to counterbalancing selection in similar traits in both sexes, or to the mode of sexual determination.
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Deciphering the mechanisms that underlie morphological and functional diversity is essential for understanding how organisms adapt to their environment. Interestingly, phenotypic divergence does not necessarily correspond to the geographic and genetic separation between populations. Here, we explored the morphological and functional divergence among populations of two genetically differentiated clades of the Moorish gecko, Tarentola mauritanica. We used linear and geometric morphometrics to quantify morphological variation and investigated how it translates into biting and CLIMBING PERFORMANCE, to better understand the mechanisms potentially underlying population and lineage divergence. We found marked morphological differences between clades, both in body size and head shape. However, much of this differentiation is more strongly related to local variation between populations of the same clade, suggesting that recent ecological events may be more influential than deep evolutionary history in shaping diversity patterns in this group. Despite a lack of association between morphology and functional diversification in the locomotor system of the Moorish gecko, straightforward links are observed between head morphology and biting performance, providing more hints on the possible underlying causes. Indeed, variation in bite force is mostly determined by size variation and sexual dimorphism, and differences between the two clades concern how sexual variation is expressed, reinforcing the idea that both social and ecological factors contribute in shaping differentiation. Interestingly, the individuals from the islets off the coast of Murcia exhibit particular morphological and functional traits, which suggests that the ecological conditions related to insularity may drive the phenotypic differentiation of this population.
Substrate properties can affect the thermal balance of organisms, and the colored integument, alongside other factors, may influence heat transfer via differential absorption and reflection. Dark coloration may lead to higher heat absorption and could be advantageous when substrates are cool (and vice versa for bright coloration), but these effects are rarely investigated. Here, we examined the effect of substrate reflectance, specific heat capacity (cp), and body size on the dorso-ventral brightness using 276 samples from 12 species of cordylid lizards distributed across 26 sites in South Africa. We predicted, and found, that bright ventral colors occur more frequently in low cp (i.e. drier, with little energy needed for temperature change) substrates, especially in larger body-sized individuals, possibly to better modulate heat transfer with the surrounding environment. By contrast, dorsal brightness was not associated with body size nor any substrate thermal property, suggesting selection pressures other than thermoregulation. Ancestral estimation and evolutionary rate analyses suggest that ventral brightness rapidly differentiated within the Cordylinae starting 25 Mya, coinciding with an aridification period, further hinting at a thermoregulatory role for ventral colors. Our study indicates that substrate properties can have a direct role in shaping the evolution of ventral brightness in ectotherms.
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