Evolution of pedal digit orientation and morphology in relation to acquisition and secondary loss of the adhesive system in geckos

Abstract

Among geckos, the acquisition of the adhesive system is associated with several morphological changes of the feet that are involved in the operation of the adhesive apparatus. However, analyses using a comparative framework are lacking. We applied traditional morphometrics and geometric morphometric analysis with phylogenetic comparative methods to morphological data, collected from X‐ray scans, to examine patterns of morphological evolution of the pes in association with the gain and loss of adhesive capabilities, and with habitat occupancy among 102 species of gecko. Padbearing gecko lineages tend to have shorter digits and greater inter‐digital angles than padless ones. Arboreal and saxicolous species have shorter digits than terrestrial species. Our results suggest repeated shifts that converge upon a similar padbearing morphology, with some modifications being associated with the habitat occupied. We demonstrate that functional innovation and habitat can operate on, and influence, different components of foot morphology.

Geometric Morphometrics Reveal Shape Differences in the Toes of Urban Lizards

“…However, increases in pad length could also be the result of indirect selection on increases in hindlimb length or total toe length. Decreases in the relative proportions of proximal toe lengths might represent a reduction in phalanges that can be seen in other pad-bearing species of lizards ( Zhuang et al 2019 ). Russell 1977 suggested that the reduction of more proximal phalanges placed the more distal phalanges in a position that better optimized usage of the claw, which has been shown to work synergistically with toepads to produce cling force in pad-bearing lizards ( Crandell et al 2014 ; Naylor & Higham 2019 ; Yuan, Wake & Wang 2019 ; Falvey et al 2020 ).…”

Early burst of parallel evolution describes the diversification of gecko toe pads

“…However, as noted earlier, the generality of padless morphologies supports the idea that extant padless morphologies are externally similar to ancestrally padless morphologies. These results also suggests that external anatomy may violate Dollo's law, although previous studies of internal anatomy highlight anatomical differences between primary and secondarily padless taxa (Russell and Gamble, 2019;Zhuang et al, 2019) supporting Dollo's law is still valid at some levels during the revolution of padless morphologies. Studies considering of the revolution of whole digits in lizards similarly highlight the context dependence of Dollo's law (Kohlsdorf and Wagner, 2006;Galis et al, 2010;Siler and Brown, 2011;Wagner et al, 2018).…”

“…It is worth noting that this approach did result in some caveats to our conclusions. Some of our extant padless taxa were likely secondarily padless (Russell and Gamble, 2019;Zhuang et al, 2019) and hence would represent transitions from padded to padless and not vice versa. In addition, such strong similarities across all padless taxa limited the possible outcomes of our trajectory analyses.…”

Ankle structure of the Tokay gecko (Gekko gecko) and its role in the deployment of the subdigital adhesive system

“…As noted above, gekkotan lizards (except for the limbless pygopodids) depart from the typical morphology of the lacertilian pes (Russell et al, 1997), the foot instead being secondarily symmetrical (Figure 1), with digits of subequal length arrayed over a broad arc (often in excess of 180°) (Russell & Oetelaar, 2016) carried on foreshortened metatarsals that are subequal in length (Powell et al, 2018;Russell et al, 1997). The secondarily symmetrical configuration of the pes is most evidently expressed in geckos that bear subdigital adhesive pads (Russell et al, 1997;Zhuang et al, 2019).…”