An ecological twist on the morphology–performance–fitness axis

Hypothesis: Natural selection shapes correlations between morphology and performance through variation in ecology (habitat use). Organism: Anolis sagrei lizards (the brown anole). Field site: A small offshore island near Great Exuma, Bahamas. Methods: I measured morphology, physiological performance [e.g. sprint speed, sprint sensitivity (the change in speed on broad versus narrow surfaces), running endurance], and habitat use (perching diameter) in natural populations of male and female lizards. I released lizards to their original sites of capture and measured differences in survival (natural selection) in each sex as a function of morphology, performance, and estimates of habitat use. Survival differences were recorded over 4 months (June–September), a period that includes the greater part of the breeding season. Results: Natural selection acted on correlations between morphology and performance that were associated with differences in habitat use among males. In most cases, selection acted on trait correlations despite the lack of any measurable selection on individual morphological or performance traits. However, morphology and performance were not correlated in females, nor did selection operate on performance variables or most morphological traits in females. Thus, hypotheses concerning selection on morphology, performance, and habitat use were supported by data for males but not females.