Life and Locomotion in a Sea of Sand: Evolution of Web-Footed Geckos of the Namib (pp. 13-28)
Authors: (Aaron M. Bauer, Villanova University, PA, USA)
Abstract: The harsh conditions of desert environments pose formidable challenges to the reptiles that inhabit them. The vegetationless sands of desert dunes are occupied by only few species capable of coping with temperature extremes, limited food and water, and difficult terrain. In the Namib Desert of southwest Africa both sand-diving and burrowing reptiles have successfully exploited such habitats. The Web-footed gecko, Pachydactylus rangei, is a burrowing gecko endemic to the Namib. It lacks the adhesive toepads typical of many geckos and is unique among the 1500 gecko species of the world in having interdigital webbing on all of its feet. The feet are structurally complex, with cartilaginous structures (paraphalanges) reinforcing the webs and supporting musculature that permits fine control of their motion. Its webs are not used as “sandshoes” as once proposed, but as shovels that operate in a very precise way to excavate sand in the formation of patent burrows. Phylogenetic analyses reveal that the Web-footed gecko is deeply nested within a species-rich lineage of pad-bearing geckos that is widespread in southern Africa. This implies that toepads have been secondarily lost in this species and that toe webbing and paraphalanges are autapomorphies that have evolved relatively recently in this lineage. Dating of phylogenetic trees suggests that the ancestor of the Web-footed gecko lineage was already present in southwestern Africa at the outset of desertification in the Miocene and that the adaptations for life in and on sand evolved as aridity increased. Other Namib dune reptiles, such as lacertids and the plated lizards have had similar histories and have been shown to be highly derived members within their respective lineages. The historical context provided by phylogenetics adds an important dimension to the study of reptile adaptation. This chapter will demonstrate how the webbed feet of P. rangei are used and how this gecko has modified the clinging toes of climbing geckos to a life in a sea of sand.