Moving in Sand: Effects of Sex and Morphology on Performance in the Sandfish Skink ( Scincus scincus )

ABSTRACT

An animal's morphology directly influences its ability to perform fundamental tasks, which can be vital to its survival and reproduction. This is especially true in harsh or extreme environments, like the shifting‐sand desert of the Sahara. Additionally, sexes can differ in their morphology, performance, or in the relationship between morphology and performance, with implications for behaviors such as habitat selection, predator avoidance, and reproduction. Despite being common across a broad geographic range, little is known of the ecomorphology and sexual dimorphism of the sandfish skink ( Scincus scincus ). To investigate this, we first validated the uses of molecular sexing protocols and morphology (hemipene eversion) to identify the sex of our animals. We then tested for differences in body size, the multivariate morphological phenotype, and coloration between the sexes. While patterns generally suggested male bias in both body size and limb dimension in concordance with previous studies, these differences were not statistically significant. Additionally, we found several exceptions to the standard color‐based sex assignment of these animals, especially for females. We then conducted an experiment to test how body size and dimensions affect performance at optimum temperatures. We quantified three different types of movement: sprinting on top of sand (used in hunting behavior), swimming under sand (an undulatory form of locomotion used in thermoregulation), and diving into sand (an important escape behavior). Overall, skinks with larger body sizes sprinted faster and swam faster through sand. Female skinks sprinted faster than male skinks even after accounting for differences in body size. Larger heads, wider bodies, and longer limbs were negatively correlated with swim speed. Diving performance exhibited the lowest among‐individual variation, did not differ between the sexes, and was not dependent on body size or shape. Finally, we found no evidence of among‐individual correlations in performance measures, suggesting each performance is independent of the others. Overall, this experiment provides insight into morphology–performance relationships across a number of ecologically important aspects of locomotion for a species inhabiting an extreme desert environment.