Chappell MA, Zuk M, Johnsen TS (1996) Repeatability of aerobic performance in red junglefowl: effects of ontogeny and nematode infection. Functional Ecology 10:578-585.

1. Repeatability is important in determining how traits are affected by selection, but it is largely unstudied for most physiological characters other than locomotory performance. We examined the repeatability of aerobic capacity, measured as maximum O₂ consumption (VO_2max), in red junglefowl, Gallus gallus. VO_2max is an integrated index of metabolic performance that can be intuitively linked to fitness because it sets the upper limit to sustainable power output.

2. We used mass residuals to determine VO_2max repeatability in adult birds, and across growth from 28-day old chicks to reproductively mature adults. We measured VO_2max during brief episodes of intense exercise in motorized running wheels. Minimal resting metabolism (VO_2mr) was measured in adults to provide an estimate of factorial aerobic scope (VO_2max / VO_2mr). We also examined the influence of sex and of infection by a common intestinal nematode, Ascaridia galli, on VO_2max.

3. There were no gender differences in adult VO_2mr or in the VO_2max of chicks. However, the VO_2max of adult males was considerably greater than that of adult females. Factorial aerobic scopes were 9.6 and 5.6 for adult males and females, respectively. Higher scope in males may be an adaptation to support intense, prolonged intermale aggression. Infection with A. galli significantly depressed the mass and VO_2max of chicks but had no effects on adults.

4. The VO_2max of adult junglefowl was highly repeatable over periods up to 180 days. In contrast, we found no repeatability of VO_2max across ontogeny for birds tested initially as chicks and again as adults. The lack of repeatability was not influenced by sex or infection status.