Effects of Hind-Limb Length and Perch Diameter on Clinging Performance in Anolis Lizards from the British Virgin Islands
Most previous studies of clinging ability in Anolis lizards have focused on how toepads adhere to smooth, flat surfaces; yet lizards in nature use a wide variety of substrates ranging from smooth to rough and narrow to broad. I used an ecologically relevant measure of performance to determine the effects of hind-limb length and substrate diameter on clinging ability for two species of Anolis lizards from the British Virgin Islands. Clinging force was greater on the 12-mm smooth, wooden dowel compared to the 33-mm one for both species. Male Anolis cristatellus had considerably larger hind limbs than female A. cristatellus and both sexes of Anolis stratulus, and consequently performed substantially better on both dowel diameters. Results suggest two important components of clinging ability on cylindrical substrates: first, the ability of lizards to reach around and interlock their limbs with the substrate increases with longer limbs and narrower substrates; and second, the limb strength to maintain a grip on the dowel when limbs wrap fully around and the ability to apply compressive force when limbs wrap only partially around the dowel. These abilities are likely related to muscle size (e.g., cross-sectional area) and may be correlated with limb length. Further studies to understand how multiple morphological traits and different substrates affect clinging performance will contribute to a better understanding of this morphology-performance-habitat use relationship.Abstract
Schematic diagram of limb postures for anoles during the clinging performance trials. I show hind-limb postures here but forelimbs grasped the dowel in a similar manner. Hind-limb lengths (HL) and dowel diameters (D) depicted in the figure are proportional to values in this study. A hind-limb length of 30 mm is typical of female Anolis cristatellus as well as male and female Anolis stratulus, whereas a hind-limb length of 50 mm is typical of male A. cristatellus (Table 1). The view is looking down from above on a vertically positioned dowel and lizard and shows the long axis of each limb segment perpendicular to the long axis of the cylindrical dowel. The black arrows indicate the direction (horizontal) the lizards were pulled to measure clinging force (i.e., the applied force). The white arrows indicate a predicted normal reference between the most distal limb segment (toes or claws) and the cylindrical surface with thin arrows for separate limbs and thick arrows for both limbs combined. Lizards best resist being pulled away from the dowel when the normal reference (white arrow) is in line with the force pulling the lizards (black arrow), as observed for lizards of both hind-limb lengths on the 12-mm dowel. Note that, for a lizard with shorter limbs on the 33-mm dowel, the limbs are too short to reach around to the side opposite the body, but a variety of limb lengths can do so on the 12-mm dowel.
The relationship between log hind-limb length and log snout–vent length for two species of Anolis lizards. Lines on the plot indicate linear relationships calculated separately for each species-sex combination.
Differences in mean (± SD) log (clinging force + 1) by species, sex, and dowel diameter. See Table 2 for statistical results.
The relationship between log hind-limb length and log (clinging force + 1) on the 12-mm diameter dowel. Lines on the plot indicate linear relationships calculated separately for each species-sex combination.
The relationship between log hind-limb length and log (clinging force + 1) on the 33-mm diameter dowel. Lines on the plot indicate linear relationships calculated separately for each species-sex combination.
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