Long or Heavy? Physiological Constraints in the Evolution of Antlers

The evolution of the investment in exaggerated secondary sexual traits is a topic of great interest for scientists. Despite antlers in the family Cervidae being one of the most interesting allometric structures, the nature of the relationships between antler and body size, and the influence of physiological factors driving the evolution of these characters, still remain unclear. In this paper, I examine these relationships in depth using the largest sample size ever studied (43 species). Under the hypothesis that antler growth may be limited by skeleton size as this process requires the allocation of huge amounts of mineral resources to the antlers, skeleton-related variables may more accurately explain these allometric relationships. The existence of physiological constraints should therefore be more clearly highlighted when studying the relationships between body size variables and the relative investment in the antler (measured as length or mass of antler per kg of skeleton). Results show that antler length is best described as being linearly related to head-body length rather than other measurements of size, and antler weight has a quadratic relationship with body mass. However, the relative investment in antler length (related to skeleton mass) is independent of body size variables, while the relative investment in antler mass has a quadratic relationship with shoulder height. The results obtained for antler mass reflect the existence of physiological constraints in the evolution of antlers, which are greater for larger sized species. On the other hand, the evolution of antler length may be linked to other factors, most probably sociobiological and biomechanical ones.