Variation in Sexually Dimorphic Traits of Male Pronghorns

Abstract

Sexually dimorphic characters in males are expected to display substantial variation if they are to be used as cues for choice of mates by females. This study examined the informative value of morphological and behavioral traits of males that were sexually dimorphic, and characteristics of their territories through an examination of the variance exhibited in male pronghorns ( Antilocapra americana ). Cheek-patch areas and lengths of horns displayed higher levels of variation than other morphological characters. Although cheek-patch areas were more variable, asymmetry in lengths of horns may provide reliable information on quality of males. Cheek-patch areas, lengths of horns, and frequency of social behaviors differed among males, whereas their territories differed in size and vegetative cover. Individual males displayed variation between their right and left cheek patches, and their frequencies of courtship changed during rut. Both timing and bout-lengths of social behaviors were negatively associated with those of maintenance behaviors, suggesting that these two classes of activities are mutually exclusive. Sizes of territories of individual males tended to be greater during summer and cover of grasses varied over years. The expression of territoriality in pronghorns is variable both among and within populations, and may represent a frequency-dependent mating strategy of males. Further study on whether variation in traits of males is correlated with variation in reproductive success of males is necessary before questions of choice of mates by females can be addressed.