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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.