Ecomorphology of the locomotor apparatus of the genus Cyrtodactylus (Gekkota, Squamata)

Adaptive radiations, clades of closely related species diversified along one or more morphological and/or ecological niche axes, garner considerable interest from evolutionary biologists. Lizard radiations diversifying along spatial niche space are hypothesised to exhibit distinct changes in body length and relative limb dimensions. One hypothesis predicts that cursorial species have relatively longer hind limbs associated with faster running speeds and relatively shorter forelimbs preventing the latter from interfering with hind limb stride frequency. Accordingly, scansorial species are expected to have relatively shorter limbs, with the fore and hind extremities of more equal length, to promote the maintenance of their center of gravity closer to the substratum. Alternatively, terrestrial species in closed habitats could benefit from relatively shorter limbs because these may reduce their entanglement with more frequently encountered obstacles, whereas scansorial species could benefit from longer limbs which would result in greater limb spans and static stability. Cyrtodactylus is a speciose and ecologically diverse gekkonid genus. From generalist ancestors this clade has repeatedly produced specialists with narrow spatial niches, such as the occupancy of karst formations, caves, granite boulders, and different strata within the arboreal niche. For cave specialists, distinct morphological changes are associated with niche occupancy. The degree of morphological diversification exhibited by the other habitat specialists remains unknown, however. We investigated whether associations exist between limb dimensions and microhabitat use in this genus, to test if either of the opposing hypotheses can be confirmed for this successful radiation. To do so we measured body length and relative limb dimensions in a large sample, including all major lineages, reconstructed the phylomorphospace occupied by the species and tested for associations between spatial niche and limb morphology. We found strong separation between spatial niche groups, although overlap exists particularly among functionally related niches such as those of granite and karst specialists