Morphological divergence, tail loss, and predation risk in urban lizards

Abstract

Urbanisation changes the structure of natural habitats and alters trophic interactions, pressuring urban species to adjust and adapt. Unlike behavioural shifts that tend to be more flexible, morphological characteristics in vertebrates are less plastic and changes may come at a greater cost. We explored the hypothesis that morphological characteristics in a tropical agamid lizard Psammophilus dorsalis are not only selected to suit altered habitat conditions in urbanised areas but reflect predation risk in urban habitats. In addition, we explored differences in tail loss in both sexes from urban and rural habitats. First, we find that predation risk did not differ between urban and rural habitats, but differed between sexes. Conspicuous courtship-coloured male lizards were more likely to be attacked compared to cryptically-coloured female lizards. Next, we find that P. dorsalis differed in key morphological characteristics, with greater urban-rural differences in males than females. Urban lizards had shorter proximal limb elements, longer 4th digits and greater body mass than rural lizards; and among males, urban lizards had significantly larger head sizes and longer distal limb elements than rural lizards. Finally, we find that the rates of tail loss differed between habitats and sexes, with urban male lizards having greater rates of tail loss than rural males and all females. Inter-sexual difference in tail loss was consistent with the difference in predation risk between sexes, but tail loss differences between urban and rural habitats could not be explained by predation risk. In sum, we find that adaptations to novel urban environments are not exclusively driven by a single promoter (e.g. predation risk) but are influenced by multiple selection pressures with associated fitness costs, such as tail loss.