Parasitism in the Endemic Galάpagos Dove (Zenaida galapagoensis) and Its Relation to Host Genetic Diversity and Immune Response

Abstract

Studies on model organisms have shown that individuals with lower genetic diversity are more susceptible to pathogens and suffer greater fitness costs than less inbred individuals. We investigated how genetic diversity, immune response, and parasitism by one hemosporidian parasite (Haemoproteus multipigmentatus) and two chewing lice (Columbicola macrourae and Physconelloides galapagensis) are related to the body condition of endemic Galápagos Doves (Zenaida galapagoensis) in six island populations. We hypothesized that (1) host genetic diversity would be negatively related to parasite abundance, (2) genetic diversity would be positively related to body condition of birds, (3) immune response would be positively related to blood parasite intensity but not to louse abundance, (4) alternatively, higher blood parasite intensity generates increased immunosuppression, leading to a lower white blood cell count and indirectly to a lower body condition, and (5) the abundances of the three parasite species would be positively correlated. Genetic diversity measured at eight microsatellite loci was an exogenous variable in the path analysis and explained 58% of the variation in body condition. Our results suggest that genetic diversity directly enhances body condition and indirectly depresses parasite abundance; this pattern was the same for the three parasite species, although it was not significant for C. macrourae. The best model suggested that blood parasites increase the activation of the immune system (measured as white blood cell counts), which may indicate an attempt of the host to control infection.