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 O₂ consumption (V̇o_2max), in Red Junglefowl, Gallus gallus. V̇o_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 V̇o_2max repeatability in adult birds, and across growth from 28-day-old chicks to reproductively mature adults. We measured V̇o_2max during brief episodes of intense exercise in motorized running wheels. Minimal resting metabolism (V̇o_2mr) was measured in adults to provide an estimate of factorial aerobic scope (V̇o_2max/V̇o_2mr). We also examined the influences of sex and infection by a common intestinal nematode, Ascaridia galli, on V̇o_2max. 3. There were no gender differences in adult V̇o_2mr or in the V̇o_2max of chicks. However, the V̇o_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 V̇o2_max of chicks but had no effect on adults. 4. The V̇o_2max of adult junglefowl was highly repeatable over periods up to 180 days. In contrast, we found no repeatability of V̇o_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.