A PRESCRIPTION FOR LONGER LIFE? BOT FLY PARASITISM OF THE WHITE-FOOTED MOUSE

Abstract

Investigation of host–parasite interactions typically reveals a negative impact of parasitism on the host species. In contrast, mounting evidence indicates that bot fly (Cuterebra sp.) infestation enhances the survival of white-footed mice (Peromyscus leucopus). We propose that life history trade-offs, namely, between reproduction and survival, can explain this counterintuitive observation. By using an extensive data set spanning a decade, 12 sites in two states, and over 30 000 mouse captures, we offer a new perspective on the effects of bot fly parasitism on white-footed mice. Analysis of persistence time corroborated earlier studies that showed significantly higher survival rates of infested mice. Although a higher proportion of infested than uninfested females were in breeding condition, secondary reproductive success appeared to be negatively impacted by parasitism via declines in the number of litters and the total number of offspring produced by infested females. Population growth rates were negatively correlated with infestation prevalence, further indicating a negative effect of parasitism. Based on the negative impact of parasitism on reproduction, we propose that enhanced survival of infested mice can be explained by the diversion of resources from reproduction to body maintenance. Parasite-induced life history shifts in which mice decrease current reproduction to promote future reproduction, such as increasing the age at maturity, may also contribute to the decline in population growth rate observed in years of high infestation prevalence.