Scaling of antler size in reindeer (Rangifer tarandus): sexual dimorphism and variability in resource allocation

Male cervids face trade-offs in allocating resources to body mass (linked to survival) and antlers (linked to reproductive success). Reindeer (Rangifer tarandus) are unique among cervids because females also possess antlers, providing an opportunity to investigate sex- and age-specific patterns of resource allocation to body mass and antlers. Using long-term (1996-2011) data on 560 reindeer, we examined how body mass and antler length varied with age and sex, and the relative allocation of resources toward antlers using scaling analysis. Body mass and antler length increased through age 5 years in males but plateaued in females at age 3 years, with males 59% greater in body mass and 146% longer in antler length by age 5 years. All age and sex categories, except yearling males and mature females, had a positive scaling (a scaling exponent greater than isometry) of antlers with body mass, with the highest relative allocation of resources toward antlers in female calves. Relative allocation toward antlers tended to increase with age in males but decrease with age in females. The observed patterns in antler and body growth are likely a reflection of sex-specific life-history strategies of reindeer whereby females have offspring yearly from puberty and males have an increased number of offspring as they mature.