Downsizing for downtown: limb lengths, toe lengths, and scale counts decrease with urbanization in western fence lizards (Sceloporus occidentalis)

Abstract

Urbanization-induced habitat loss and alteration causes significant challenges for the survival of many species. Identifying how species respond to urbanization can yield insights for the conservation of wildlife, but research on reptiles has been narrowly-focused. We compared morphology among four populations of western fence lizards (Sceloporus occidentalis) to determine whether a common native species affected by urbanization exhibits morphological differences consistent with habitat use. We quantified habitat differences across four sites in Los Angeles County, California, USA that varied in level of urbanization, measured how lizards used microhabitats, and assessed variation in body size, limb length, toe length, and scalation of lizards collected from each site. Urban and suburban populations of fence lizards mostly used human-made substrates while lizards from more natural areas mostly used natural woody substrates. Lizards from the most urban site also exhibited the widest breadth of substrates used, indicating that urban sites might offer more variable microhabitats. Urban lizards had reduced limb lengths and toe lengths consistent with how they used microhabitats and other habitat characteristics (e.g., percent impervious surface cover). Urban lizards also had fewer dorsal scales, which might be associated with changes in ambient temperature (e.g., urban heat island effect), given that lizards with fewer and larger scales typically have reduced evaporative water loss. Our results uniquely differ from past studies on lizard responses to urbanization, indicating that work on diverse taxa is necessary to assess the potential varied pathways of morphological adaptations to urban environments.