Ontogenetic allometry of the digital rays of the leopard gecko (Gekkota: Eublepharidae; Eublepharis macularius)

Abstract

The role of allometry in producing the variation in autopodial morphology observed among the lizards is not well understood. Allometry of metapodial and digit lengths in the manus and pes of the primitively padless gekkotan (Eublepharis macularius) is explored using maximum‐likelihood repeated‐measures ANCOVAs with body length as the covariate. Estimated variance–covariance matrices differed significantly within and between autopodia, and integration was stronger among the metapodials than the digits. The first metapodial and the first digit of each autopodium exhibit the strongest covariances with each of the remaining components in each variance–covariance matrix, suggesting that the lengths of the first rays are important for allometric integration of both manus and pes. Metapodials scale isometrically and digits negatively allometrically; both display allometric heterogeneity among themselves in both autopodia. Both autopodia exhibit changes in proportion over the ontogenetic size range, attributable to variation in scaling among the components of the rays. Allometric coefficients do not vary among pedal digits, despite differences in phalanx number, although phalanx number is associated with differences in slope in the manual digits. This is suggestive of heterogeneity in allometry among the manual phalanges, which thus may be associated with variation in phalanx length within gekkotan digits.

Evolution of the Gekkotan Adhesive System: Does Digit Anatomy Point to One or More Origins?

“…3, branches 4, 5; Table 1) (Russell and Bauer 2008). The ancestral state reconstruction for the Diplodactylidae, and the Eublepharidae + (Sphaerodactylidae + [Phyllodactylidae + Gekkonidae]) indicates a relative shortening of the intermediate phalanges (phalanges 2 and 3 of digit IV, Powell et al 2018), which is associated with the overall relative shortening of the digits of geckos when compared with other lizards (Russell et al 1997). A difference in the extensor musculature of the digits distinguishes the Diplodactylidae + Carphodactylidae from the remainder of the Gekkota (Fig.…”

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

“…Specimens were sandwiched between two sheets of Plexiglass before radiography to control for orientation and parallax. Only specimens that could be appropriately oriented were used for obtaining individual interdigital angles, digit lengths, and metatarsal lengths, as per the procedures of Russell et al () and Powell, Osgood, and Russell () (Figure ).…”

“…For the traditional morphometric analysis, the following variables were measured in ImageJ () and calculated for the 65 specimens used for the geometric morphometric analysis and combined with data from Russell et al (). To obtain the sum of total phalangeal lengths within each digital ray (wherein a digital ray consists of two moieties: the metatarsal moiety and the phalangeal moiety comprising the sum of the phalangeal lengths—see Powell et al, ), we subtracted metatarsal length from length of the digital ray. Interdigital angle data were collected by extending the longitudinal axes of the metatarsals proximally until they intersected with the axis of their neighboring metapodials (Russell et al, ) and with those of more distant digital rays, including the intersection of the axes of digits I and V (Figure ).…”

“…As demonstrated by our geometric morphometric analysis, arboreal, ancestrally padless species, such as Saltuarius salebrosus, often have a highly symmetrical foot despite the absence of toepads. A study similar to that of Powell et al (2018), examining ontogenetic growth in such species, with the simultaneous measurement of metatarsal head shape and interdigital angle measurement, could help determine the mechanisms underlying changes in interdigital angles. In addition, behavioral analyses, similar to that of Russell and Oetelaar (2015), would reveal how such species use their claws in combination with the broad digital spread that they possess (Naylor & Higham, 2019).…”

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).…”