Evolutionary approaches for studying functional morphology: examples from studies of performance capacity.

Performance studies have long been a cornerstone of evolutionary studies of adaptation because of their purported importance for fitness. Nevertheless, for most systems, the mechanistic link among habitat use, morphology and performance is poorly understood. Further, few studies consider how behavior affects the relationship between morphology and performance. Here, I highlight the utility of considering both of these neglected areas by discussing studies in two systems: (1) the evolution of habitat use in Caribbean Anolis lizards, and (2) the evolution of limb function in desert lizards. Caribbean Anolis lizards partition the habitat via selection of different perch diameters, and surface diameter also exerts a strong effect on locomotor performance. Phylogenetic analyses show that Anolis species tend to avoid using perches in which their performance is submaximal, and also show that species with large performance breadths use a greater range of habitats. The underlying basis of this performance to habitat use link is a trade-off between the ability to sprint quickly on broad surfaces and the ability to move effectively on narrow surfaces. Studies of the kinematics of high-speed locomotion in five morphologically distinct lizard species reveal that some species exhibited behaviors that greatly enhanced their performance abilities relative to other species, suggesting that behavior can play a key role in the link between morphology and performance. Overall, these findings underscore the value of using a mechanistic approach for studying the links between habitat use, morphology and behavior.