Ontogeny, phylogeny, and mechanisms of adaptive changes in evaporative water loss in geckos

Body-size dependence of metabolic rate, body surface and scale morphology
complicate disentangling the contribution of these characteristics to
adaptive changes in total evaporative water loss (TEWL) of reptiles. To
separate adaptive changes from size-related dependence, we compared intra-
and interspecific scaling of several candidate traits in eyelid geckos
(Eublepharidae), a group exhibiting large variation in body size and TEWL.
The intraspecific allometry of TEWL of an eublepharid species fits the
geometric surface-mass relationship. However, evolutionary shifts to both
higher and lower evaporation were strongly correlated with habitat aridity
and cannot be explained by shifts in body size alone. The intraspecific
allometry of standard metabolic rate is nearly the same as the
interspecific allometry. Unlike for mammals and birds, this pattern rules
out respiratory water loss as a driver of the adaptive changes in TEWL
among eublepharids. Scale morphology was independent of TEWL variation as
well, but the correlation between cutaneous water loss and TEWL suggests a
crucial role of skin permeability in adaptation to habitat aridity. Our
analyses demonstrate how powerful a comparison of intra- and interspecific
allometries can be for detecting body size-dependent mechanisms of
adaptive changes in ecophysiological traits correlated with body size.