Does lactation lead to resource allocation trade-offs in the spotted hyaena?

Abstract

Life history theory predicts that when food intake and body reserves are insufficient to maintain all life processes, resource allocation trade-offs should occur. Lactation is costly and requires increased food intake. In spotted hyaenas, energy expenditure on lactation is high, particularly for mothers rearing twin litters, and foraging effort and food intake are influenced by social status. We investigated whether lactation in this species results in a reduction in resource allocation to immune processes sufficient to increase parasite infection. We expected higher parasite infection in lactating than non-lactating females, in mothers nursing twin than singleton litters, in females of lower than higher social status and in less than more experienced foragers. We quantified Ancylostoma egg load (AEL) and the presence of oocysts of Cystoisospora spp. as a proxy measure of immune function in 58 females. Lactating females were significantly more often infected with Ancylostoma, and their AEL was higher than in non-lactating females. Females nursing twins had significantly higher AELs than those nursing singletons. As social status increased, AELs significantly declined. This relationship was modulated by lactation status and litter size, being strongest in non-lactating females, moderate in females with twin litters and weakest in females with singleton litters. The decrease in AEL with increasing social status was greater for experienced than inexperienced females. Concurrent infection with Cystoisospora significantly increased with increasing AEL. Our results provide evidence for a resource allocation trade-off in lactating spotted hyaenas.