Fluctuating Asymmetry in the Antlers of Moose (Alces alces): Does it Signal Male Quality?

We studied fluctuating asymmetry (FA) in the number of antler points from a total of 2126 moose (Alces alces) bulls killed during the hunting season in central Norway over a period of 23 years. All age groups showed a positive relation between FA and the number of antler points on the largest antler (antler size, AS). Based on the assumption that only the highest-quality individuals can produce the largest and most symmetrical sexual traits, the results did not support the hypothesis that FA in sexual traits signals the quality of the possessor. However, a partial correlation analysis revealed a negative relation between FA and carcass mass when controlling for AS. Thus relatively larger bulls in relation to their antler size produce more symmetrical antlers compared with relatively smaller bulls. Similarly, a regression analysis between FA and AS in the different age groups revealed a significant age-dependent decrease in the regression coefficients. This suggests that older bulls are more able to cope with environmental stress during the development of the antlers than younger bulls. Thus, for a given antler size, the age of the bull can be signalled through the FA. We therefore suggest that quality signalling by antler size and FA could be an additional component of sexual selection on moose antlers.