LIFE-HISTORY CORRELATES OF HORN ASYMMETRY IN MOUNTAIN GOATS

Abstract

Fluctuating asymmetry (FA) refers to small random deviations from perfect bilateral symmetry. Because FA reflects the ability of individuals to undergo stable development, it may provide a potential measure of individual quality. We assessed whether horn asymmetry was related to life-history traits in individually marked mountain goats (Oreamnos americanus) over 10 years. Horn length exhibited FA and was related positively to absolute asymmetry in both sexes. Relative asymmetry in horn length did not vary with either sex or age. Horns of surviving juvenile (1- and 2-year-old) males were more symmetrical than horns of those that died, but horn asymmetry did not affect survival of juvenile females or adults of either sex. Horn asymmetry was not related to body condition in juveniles of either sex or in adult males, but adult females with symmetrical horns were in better condition than those with asymmetrical horns. Similarly, horn asymmetry was related negatively to body mass in adult females but not in other sex–age classes. Horns of dominant females were more symmetrical than those of subordinate females. Females that produced a young in their year of capture had more symmetrical horns than females that did not reproduce, and horn asymmetry was correlated negatively with long-term reproductive success in females. Nonetheless, asymmetry in horn length of females did not influence survival of young and was not related to age of primiparity. Analysis of our results indicates that asymmetry in horn length is a phenotypic marker of individual quality in females but does not point to a strong relationship between horn asymmetry and life-history traits in adult males.