Intra-specific variation of thermal performance, skin reflectance and body size partially co-vary with climate in a lizard

Thermal adaptation theory posits that variation of thermal traits such as those affecting thermal budgets and the performance of ectotherms should be associated with climate gradients. Under a simple scenario, thermal traits should also co-vary to shape optimal thermal phenotypes under a particular climate. However, geographical variation and covariation of thermal traits can result from other sources of selection and a wide range of other mechanisms. Here, we explore variation and covariation of skin reflectance (melanization), body size and thermal performance traits among three populations of the lizard Cordylus cordylus, a species endemic to South Africa. We also examine relationships between skin reflectance and substrate reflectance, body size and crevice size to test alternative hypotheses. We found partial support for predictions of thermal adaptation to climate regimes for body size, melanization and chill-coma recovery time. Darker lizards also performed optimally at higher temperatures than lighter coloured lizards but there was limited individual covariation between morphological and performance traits. Despite partial support for thermal adaptation, the complex interactions between sex and body size and between substrate reflectance and size underlying skin reflectance emphasized the importance of testing multiple hypotheses when exploring drivers of thermal trait variation within species.

WE, Perera A, Pérez-Mellado V. Escaping predators on vertical surfaces: Lacerta perspicillata in limestone quarries of Lithaca

Escape behavior of the Mediterranean lizard Lacerta perspicillata was studied experimentally in a limestone quarry at Lithica on the island of Menorca, Balearic Islands, Spain. These lizards are exposed to avian predators while active on vertical rock faces. Simulated kestrel attacks using a cardboard model elicited escape responses from nearly all lizards approached. Methods of escape included entering a crevice, retreating over or around an edge, running behind a shrub growing against the rock surface, running behind a shrub and dropping to the ground ("bush to ground"), and retreating under or behind a rock isolated from a rock face. Most lizards fled directly to the closest available refuge or to alternative refuges only slightly farther away. Nevertheless, lizards that initially perched near crevices more frequently fled to other types of refuge than lizards that were initially near other refuges. The latter usually fled to the closest refuge. Lizards predominantly fled parallel to the ground or directly toward it (down) into a refuge regardless of the direction of attack (above, below, straight on). Direction of attack affected the type of refuge used. Lizards approached from above were more likely to flee to bush-ground or crevices than those approached from below or the same height. Straight-line retreat directly to a refuge appears to be the most viable escape strategy for these lizards when faced with attacks by avian predators, but the direction of attack may influence decisions based on risk.

Head shape and bite performance in xenosaurid lizards

Bite performance in lizards influences many aspects of the animal's lifestyle. During feeding, inter- and intrasexual interactions, and defensive behavior, the ability to bite hard might be advantageous. Although biomechanical considerations predict clear relations between head shape and bite performance, this has rarely been tested. Here we investigate the effect of head shape on bite performance in three closely related species of xenosaurid lizards. Our data show that in this family of lizards, bite performance is mainly determined by head height, with high headed animals biting harder than flat headed ones. Species clearly differ in head shape and bite performance and show a marked sexual dimorphism. The dimorphism in head shape also results in an intersexual difference in bite performance. As head height is the major determinant of bite performance in xenosaurid lizards, trade offs between a crevice dwelling life-style and bite performance seem to occur. The evolutionary implications of these results are discussed. J. Exp. Zool. 290:101-107, 2001.