Male mating behaviour and patterns of sperm precedence in Arctic ground squirrels

Abstract

Ground squirrels (genusSpermophilus) display considerable interspecific variation in male reproductive behaviour. Although male Arctic ground squirrels,S. parryii plesius, are territorial during the mating period, males in several other species ofSpermophilusare not. To begin exploring the reasons for this behavioural difference, patterns of mating behaviour and sperm precedence were characterized for a free-living population ofS. parryii plesius. Twenty females that were monitored continuously throughout behavioural oestrus consorted and presumably copulated with a mean of 1.9±0.8 males during a single period of sexual receptivity. A combination of electrophoretic and DNA fingerprinting analyses revealed that more than 90% of pups in litters (N=11) reared by females that consorted with two or more males were sired by a female's first mate. The percentage of young sired by each of a female's consorts did not vary with either consortship duration or the interval between consortships by different males. Instead, the only consistent correlate of paternity was consortship order. Both pre-consortship calling and post-consortship defence of females were significantly associated with first consortships, suggesting that males were able to distinguish unmated females from females that had already copulated. Because the probability of siring young should influence which females are preferred as mates and how males compete for access to those females, comparative studies of sperm precedence patterns may yield insights into the evolution of interspecific variation in male mating behaviour.