Behavioural correlates of parasitism and reproductive success in male eastern chipmunks, Tamias striatus

An individual’s fitness is estimated by its lifetime reproductive success. In the polygynandrous sciurid mating system, male reproductive success is determined by an individual’s success in locating and defending receptive females. Personality traits are differences in behavioural reactions that are heritable, consistent across contexts and over time, and may have important fitness consequences. Little research has been conducted on the effect of personality on success in the competition for mates. We examined the relationship between behavioural traits, parasite load and male reproductive success (the number of offspring sired in one year) in the eastern chipmunk. We expected that behavioural traits would affect male reproductive success either directly, through their effect on success in locating and/or defending females, or indirectly, through their effect on parasite load. We measured trappability, activity level/exploratory behaviour, struggle rate and ecto- and endoparasite load. Eighty-two chipmunks (29 adult males, 24 adult females, 29 juveniles) were genotyped to determine paternity. Assuming that trappability is an indicator of boldness, we found that bolder males had more offspring when controlling for endoparasite load. Moreover, bolder males had a higher endoparasite load, caused either by depleted energy reserves or the immunosuppressive effects of testosterone. We conclude that boldness affects reproductive success both directly and indirectly (via parasite load) in male chipmunks; however, there appears to be a trade-off between the positive direct effect and the negative indirect effect on reproductive success.