Within-individual covariation masks an among-individual performance tradeoff in the prairie lizard

Abstract

To understand fitness consequences of performance, one must determine how underlying physiological traits result in and constrain performance. Biochemical and mechanistic investment in a performance trait may cause decreased performance elsewhere: a performance tradeoff, indicating performance specialization in a population. (Co)variation exists within individuals, and among individuals, populations, and species. Conflicting patterns of among-individual and within-individual covariation may eliminate, or mask, the relationship at the phenotypic level. Multivariate mixed-effects models (MMMs) model within-individual and among-individual variation separately. We used MMMs to test for relationships between physiological and performance traits associated with locomotion in the prairie lizard Sceloporus consobrinus, and tested for tradeoffs at multiple hierarchical levels. We then compared these results to the conventional Pearson correlations. We found a significant among-individual tradeoff between endurance and climbing speed. Positive covariation within individuals masked the tradeoff at the phenotypic level. Sprint speed positively covaried with climbing speed. Excluding anaerobic scope, which was associated with endurance, no measured physiological traits were predictive of locomotor performance. These data indicate that performance specialization exists among prairie lizards and contribute to a growing body of literature that have successfully used MMMs to uncover performance tradeoffs which may have been masked using conventional methods.