Phylogenetic analysis of maximal oxygen consumption during exercise (V̇O2max) and ecological correlates among lizard species.

The maximum amount of oxygen consumed during forced exercise (V̇O2max) sets the upper limit to the effort that can be sustained over relatively long periods and can limit activity levels in nature. Among ectotherms, V̇O2max is primarily affected by body size and body temperature, but it should also coadapt with behavior, ecology, and life history aspects. We compiled published data from 11 different families of lizards, including 58 species and 7 populations (total 65 data points) and tested whether V̇O2max was related to diet (herbivore, insectivore, insectivore/carnivore, carnivore, and omnivore), climate (tropical, temperate, and arid), nocturnality, viviparity, or family. We fitted models that included body mass and measurement temperature as covariates, and all possible combinations of other independent variables using ordinary least-squares (OLS) and phylogenetic regressions assuming an Ornstein-Uhlenbeck model of residual trait evolution (RegOU). The sum of Akaike weights for each independent variable revealed viviparity (∑wi=0.996) and the combined set of dummy variables coding for helodermatids, varanids, and skinks (∑wi=0.996) as the most important predictors. These three families had relatively high V̇O2max. They are composed mainly of active foragers that probably benefit from higher V̇O2max. Viviparity had a negative effect on V̇O2max. Ecological or behavioral factors associated with viviparity (e.g., activity levels), but not included here, may explain this effect. The average allometric slope of V̇O2max from the top eight models (which accounted for 99% of the cumulative evidence) was 0.803, which is similar to that reported previously for lizards and for mammals in general.