Configuration of the setal fields of Rhoptropus (Gekkota: Gekkonidae): functional, evolutionary, ecological and phylogenetic implications of observed pattern.

Many gekkotans possess seta-bearing adhesive subdigital pads. Details of setal structure, however, are largely based upon putatively exemplary fibrils deemed typical of the species. Little is known of the pattern of configuration of the setae across the subdigital pads and how great, if any, the variance in structure and dimensions is. To understand setal fields as functional entities, as opposed to individual setae, it is necessary to consider this pattern. Additionally, gekkotans within individual radiations occupy different environments and potentially are substrate-specific in terms of the locomotor surface exploited. To investigate these issues, we herein examine the configuration and dimensions of seven species of the gekkotan genus Rhoptropus, and an outgroup taxon, Chondrodactylus bibronii. All of these taxa are rupicolous and the array of rock surfaces exploited by this cluster of taxa is extensive. Our results show that setal field configuration follows a predictable pattern, both from one digit to another within a species, and between homologous digits and anatomical locations between species. One species, Rhoptropus afer, a more terrestrial taxon, exhibits significantly shorter setae and a smaller subdigital pad area than do its congeners, but exhibits the same overall pattern of setal arrangement. Our findings have implications for the understanding of the evolution of adhesive structures, and for the principles used for generating and manufacturing biomimetic artificial microfibrillar arrays.