Energetic costs of performance in trained and untrained Anolis carolinensis lizards.

The energetic costs of performance constitute a non-trivial component of animals' daily energetic budgets. However, we currently lack an understanding of how those costs are partitioned among the various stages of performance development, maintenance and production. We manipulated individual investment in performance by training Anolis carolinensis lizards for endurance or sprinting ability. We then measured energetic expenditure both at rest and immediately following exercise to test whether such training alters the maintenance and production costs of performance. Trained lizards had lower resting metabolic rates than controls, suggestive of a maintenance saving associated with enhanced performance as opposed to a cost. Production costs also differed, with sprint-trained lizards incurring a larger energetic performance cost and experiencing longer recovery times compared with endurance trained and control animals. Although performance training modifies metabolism, production costs are probably the key drivers of trade-offs between performance and other life-history traits in this species.

How Do We Measure the Cost of Whole-Organism Performance Traits?

SYNOPSIS: Whole-organism performance traits, such as maximal speed and endurance capacity are undoubtedly costly, but we know little about how or when all of the costs associated with performance are paid to individuals or how to measure them. To understand how performance traits might be involved in trade-offs with other life-history traits it is critical to determine the development, production, and maintenance costs of performance traits, as well as how each of these changes with increased or decreased use of the performance trait. We discuss the advantages and disadvantages of several potential phenotypic measures of dynamic whole-organism performance that may be used in life-history studies, including direct performance measures; metabolic rates; ecological cost of transport; and changes in metabolic rate after training. We use the first approach, direct performance measures, to show trade-offs between endurance capacity and several traditional life history variables in phrynosomatid lizards. The largest problem currently in determining the costs of performance traits and how those costs might lead to life-history trade-offs is that there are estimates of performance costs in very few taxa, and when there are, those species typically are not studied with respect to "traditional" life-history traits.

A performance-based cost to honest signalling in male green anole lizards (Anolis carolinensis).

Sexual signals are considered costly to produce and maintain under the handicap paradigm, and the reliability of signals is in turn thought to be maintained by these costs. Although previous studies have investigated the costly nature of signal production, few have considered whether honesty might be maintained not by the costliness of the signal itself, but by the costs involved in producing the signalled trait. If such a trait is itself costly to produce, then the burden of energetic investment may fall disproportionately on that trait, in addition to any costs of signal maintenance that may also be operating. Under limited resource conditions, these costs may therefore be great enough to disrupt an otherwise reliable signal-to-trait relationship. We present experimental evidence showing that dietary restriction decouples the otherwise honest relationship between a signal (dewlap size) and a whole-organism performance trait (bite force) in young adult male Anolis carolinensis lizards. Specifically, while investment in dewlap size is sustained under low-resource condition relative to the high-resource treatment, investment in bite force is substantially lower. Disruption of the otherwise honest dewlap size to bite force relationship is therefore driven by costs associated with the expression of performance rather than the costs of signal production in A. carolinensis.