Life-history correlates of horn asymmetry in mountain goats

Fluctuating asymmetry (FA) refers to small random deviations from perfect b ilateral symmetry. Because FA reflects the ability of individuals to underg o stable development, it may provide a potential measure of individual qual ity. 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 i n both sexes. Relative asymmetry in horn length did not vary with either se x or age. Horns of surviving juvenile (1- and 2-year-old) males were more s ymmetrical than horns of those that died, but horn asymmetry did not affect survival of juvenile females or adults of either sex. Horn asymmetry was n ot related to body condition in juveniles of either sex or in adult males, but adult females with symmetrical horns were in better condition than thos e with asymmetrical horns. Similarly, horn asymmetry was related negatively to body mass in adult females but not in other sex-age classes. Horns of d ominant females were more symmetrical than those of subordinate females. Fe males that produced a young in their year of capture had more symmetrical h orns than females that did not reproduce, and horn asymmetry was correlated negatively with long-term reproductive success in females. Nonetheless, as ymmetry in horn length of females did not influence survival of young and w as not related to age of primiparity. Analysis of our results indicates tha t 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.