Repeatability of aerobic performance in Red Junglefowl: Effects of ontogeny and nematode infection

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 O-2 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 influences of sex and 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 effect 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.