Skink ecomorphology: forelimb and hind limb lengths, but not static stability, correlate with habitat use and demonstrate multiple solutions

Interspecific variation in animal form, function and behaviour is often associated with habitat use, implying co-adaptation. Numerous studies of the 'ecomorphs' of Greater Antillean anoles support this generality, but no other lizard group has shown unambiguous, consistent relationships between limb length and habitat use. We tested for such relationships in lygosomine skinks, a speciose and geographically widespread group that exhibits tremendous variation in relative limb length, has repeatedly invaded terrestrial, saxicolous and arboreal habitats, and uses a narrow range of substrates within these habitats. We combined new morphometric measurements of museum specimens and data from the literature (N = 101 total species) to determine if biomechanically founded ecomorphological predictions could successfully describe relationships of habitat with body size and with size-adjusted limb size, while also testing for differences among clades and for interactions between habitat and clade. In phylogenetically informed statistical analyses, both body size and size-adjusted hind limb length had a significant clade-by-habitat interaction and this interaction approached statistical significance for size-adjusted forelimb lengths. The ratio of forelimb to hind limb length varied among clades. However, size-adjusted limb spans, stance area and static stability were unrelated to either habitat or clade. Overall, although limbs tend to be longer in climbing than in terrestrial skinks, the clade-dependent nature of this relationship suggests that lygosomine skinks have achieved multiple solutions to similar selective regimes. We propose that longer limbs are probably more important for active climbing than for static clinging, and suggest that climbing and clinging ability may be somewhat independent.