Divergence in locomotor performance, ecology, and morphology between two sympatric sister species of desert-dwelling gecko

Abstract

The functional and evolutionary implications of morphological diversification have been addressed for several groups of vertebrates. Although the mechanisms of gecko adhesion have received considerable attention, little is known regarding locomotor performance of geckos in nature, and how this might relate to morphological diversity. In this study we examine locomotor performance of two sympatric sister species of geckos of the genus Rhoptropus (Rhoptropus afer and Rhoptropus bradfieldi) found in the coastal desert regions of Namibia. One species (R. afer) commonly runs on sandy substrates and moves between isolated rock sheets, whereas the other species (R. bradfieldi) commonly lives and runs on isolated boulders. The morphology of R. afer is extremely divergent from its sister species and all other species in the genus. We initially recorded the inclination of the substrate in which the lizards were found in order to characterize the habitat of each species. We then quantified maximum speed and acceleration on a level 1-m trackway, and also during escapes in the field. We found that R. bradfieldi occupies steeper surfaces than those occupied by R. afer. On the trackway and in nature, R. afer runs faster than R. bradfieldi, although the differences in locomotor performance between the species are greater for the field measurements. Rhoptropus afer commonly runs for more than 2 or 3 m, whereas R. bradfieldi commonly runs less than 50 cm during an escape sprint. Our main conclusions are that: (1) R. afer attains higher maximum speeds when escaping under controlled and field conditions, although the magnitude differs between conditions; and (2) hindlimb morphology correlates with maximum running speed in R. afer, but not in R. bradfieldi. Similar to the well-studied Anolis lizards, we propose that these two gecko species represent distinct and highly divergent ecomorphs. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 860‐869.