Sexual shape dimorphism in Alpine chamois (Rupicapra rupicapra) horns: Using horn curvature in sex identification

Abstract

© 2015 by De Gruyter 2015. We used horn outlines with elliptic Fourier analysis to quantify horn shape as well as horn outline areas to quantify horn size in 26 Alpine chamois (Rupicapra rupicapra) skulls of known sex from Serbia. The aim of this study was to investigate the degree of horn curvature that characterizes each sex and devise a methodology for using horn shape to determine sex. We observed a grouping pattern that exactly corresponded to each sex by analyzing Fourier transformed and normalized outline data with holding sexes unknown by exploratory cluster and discriminant analyses. Curvature was the most important determinant of chamois horn shape, and females were found to have less curved horns than males. Horn size was also a significant factor contributing to sexual dimorphism, whereas allometric scaling was similar in both sexes. We argue that horn growth is characterized by elongation of the horn axis in females and increasing curvature in males, and that these processes are constrained to later years of individual's life when the overall horn size changes very little. Our conclusions fit well with published data on chamois social structure and behavior suggesting that selective pressure acting on horn shape changed with increasing levels of sexual size dimorphism.