The relative effects of reproductive condition, stress, and seasonality on patterns of parasitism in wild female black howler monkeys (Alouatta pigra).

Parasitic infections in wildlife are shaped by host-related traits including individual reproductive condition. It has been argued that female primates are more susceptible to infectious diseases during pregnancy due to short-term changes in immune function that result in reduced ability to combat infections. Likewise, lactation, which is the most energetically expensive state, may affect immunity and infection risk due to tradeoffs between milk production and maintenance of immune function. Here, we examine the degree to which parasite prevalence and parasite richness are affected by female reproductive condition and stress levels in wild female black howler monkeys (Alouatta pigra). Over the course of one year, we collected fresh fecal samples from 15 adult females belonging to seven black howler groups living in Escárcega, Mexico. Fecal samples were used for parasitological analysis and for measuring fecal glucocorticoid metabolites (i.e., stress biomarker). We found that the prevalence of intestinal parasites and parasite richness did not differ among non-pregnant, pregnant, and lactating females. Fecal glucocorticoid metabolite levels increased significantly during pregnancy and during the first month of lactation, and positively predicted the probability of Controrchis biliophilus infection. Parasite prevalence and richness decreased during the months of increased rainfall. We conclude that reproductive physiology has limited consequences on intestinal parasitic infection risk in female black howler monkeys and that seasonal environmental fluctuations have greater effects.