Asymmetry in antler size in roe deer (Capreolus capreolus ): an index of individual and population conditions.

Fluctuating asymmetry (FA) refers to small random differences that occur between the right and the left sides of bilateral characters. Under the hypothesis that the degree of FA in secondary sex traits reflects the ability of males to cope with environmental stress, and consequently reflects individual quality, a negative relationship is expected between FA and the trait size. Additionally, selective mortality acting preferentially on individuals in poor condition, presumably more asymmetric, should lead to a decrease in FA with age. We tested these hypotheses on roe deer (Capreolus capreolus) antlers, analysing the FA pattern in antler size from individuals culled over 18 years in a single population. Absolute asymmetry significantly decreased with age, and tended to decrease with antler size, at constant carcass mass, within age classes. Moreover, increase in the population density negatively affected carcass mass and antler size, and resulted in a significant increase in the degree of asymmetry in antlers. These results suggest that antler development in roe deer represents a reliable signalling of individual quality. Moreover, due to the deciduous nature of antlers, asymmetry in antler size appears to be a valuable indicator of the current environmental conditions encountered by populations.