Social Dominance Is Associated with Individual Differences in Heart Rate and Energetic Response to Food Restriction in Female Red Deer

Abstract

Energy expenditure is a key mechanism underlying animal ecology, yet why individuals often differ in metabolic rate even under identical conditions remains largely unexplained. Individual variation in metabolism might be explained by correlations with other behavioral and physiological traits, with individual syndromes having environment- or state-dependent costs and benefits to fitness. We tested whether social rank within herds of female red deer is associated with individual differences in resting heart rate, an index of metabolic rate, and energetic response to monthly periods of food restriction during winter in a large outdoor enclosure near Vienna, Austria. Social rank had a strong positive effect on average daily heart rate, independent of the effects of food intake, air temperature, body temperature, and body mass. Subordinate individuals had lower heart rates than dominants, and consequently they suffered lower rates of body mass loss during periods of restricted pellet food supply. A greater capacity to minimize energy requirements might benefit the survival of subdominant female red deer during periods of negative energy balance in winter. Our study provides empirical support in a large mammal for linkages in behavior and metabolism within individuals that have environment-dependent consequences to the energy budget.