Abstract
Summary A range of physiological traits are linked with aggression and dominance within social hierarchies, but the role of individual aerobic capacity in facilitating aggression has seldom been studied. Further, links previously observed between an individual's metabolic rate and aggression level may be context dependent and modulated by factors such as social stress and fcompetitor familiarity. We examined these issues in juvenile Ambon damselfish, Pomacentrus amboinensis, which display intraspecific competition for territories during settlement on coral reefs. Individuals were measured for routine metabolic rate, aerobic scope (AS) and anaerobic capacity using intermittent‐flow respirometry before dyadic dominance contests. Post‐contest, fish were measured for metabolic rate in isolation and while interacting with their previous competitor or a stranger in adjacent transparent respirometers. In arena contests, AS was correlated with aggression and dominance, while routine metabolic rate and anaerobic capacity were not related to dominance. Post‐contest, subordinates showed a rise in metabolic rate and decrease in available AS, presumably due to social stress. Dominants increased metabolic rate in the presence of a previous competitor, possibly due to the stresses of hierarchy maintenance. Metabolic rate during aggressive interactions did not approach that measured during exhaustive exercise, suggesting individuals do not fully utilise their AS during aggression. A greater AS may, however, allow faster post‐contest recovery. These results demonstrate a link between AS and dominance during intraspecific competition for territory. Selection on AS could therefore follow, either indirectly through correlations with other traits influencing resource‐holding potential, or directly if AS carries benefits important for territory acquisition or holding, such as an enhanced capacity to cope with socially induced stress.
Highlights
Variation in aggression among individuals within a number of animal species can determine status within social hierarchies, which in turn affects life-history strategies, several studies have documented large energetic costs of physical activity during aggressive encounters (Briffa & Sneddon 2007), the effects of individual aerobic capacity on aggression have been mostly overlooked
Individuals were measured for routine metabolic rate, aerobic scope (AS) and anaerobic capacity using intermittent-flow respirometry before dyadic dominance contests
We used a three-parameter exponential function to determine the rate of oxygen uptake immediately following exhaustive exercise, estimated as the y-intercept of the plot of oxygen uptake versus time. This method for determining maximal metabolic rate (MMR) was required for two reasons: (i) the first 1 min after transfer of fish to the respirometers was excluded from analyses so that adequate mixing within the chamber and external circuit could occur, providing accurate measures of water oxygen concentration; and (ii) the recovery of individuals after exercise was rapid (Fig. S1, Supporting information), and we aimed to estimate oxygen uptake as close to the cessation of exercise as possible
Summary
Variation in aggression among individuals within a number of animal species can determine status within social hierarchies, which in turn affects life-history strategies, several studies have documented large energetic costs of physical activity during aggressive encounters (Briffa & Sneddon 2007), the effects of individual aerobic capacity on aggression have been mostly overlooked. An additional benefit of a large AS might be that any effects of social stress on metabolic rate could have a relatively small effect on the proportion of remaining AS available for other physiological tasks (e.g. growth, activity, digestion) following an aggressive encounter. Some species appear to display increased aggression towards neighbours as compared to strangers (Mu€ller & Manser 2007; Schradin, Schneider & Lindholm 2010). This may occur when neighbours present more of a threat than strangers, but the situations in which this occurs and the implications for energy expenditure and AS usage are unknown. More information on the metabolic consequences of distinguishing between neighbours and strangers would be useful for understanding the energetic basis of trade-offs associated with resource-holding and territorial defence
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