Meeting Abstract
Haemosporidian parasites, including those responsible for avian malaria, can have substantial negative fitness consequences for their avian hosts. In areas where the parasites have been recently introduced, acute infection can result in rapid mortality. Where the parasites are endemic, infection does not have similar effects, but chronic infection can reduce both annual survival and reproductive success in some bird species. As a result of the parasites’ global distribution and the sublethal effects of chronic infection, malaria-causing parasites are frequently used as a model to test the role of parasites in shaping life history evolution. However, the mechanisms underlying the relationship between chronic malaria infection and fitness are not well understood. We investigated some physiological consequences of low intensity, chronic infection in adult male red-winged blackbirds (Agelaius phoeniceus) from a population where approximately 95% of individuals are infected. We used a medication experiment with birds held in outdoor aviaries to examine the effects of infection on 1) cellular damage, 2) tissue repair, and 3) immune activation. Higher parasite burdens were correlated with lower hematocrit and an increase in red blood cell production. Birds that received antimalarial medication had higher hematocrit and hemoglobin, reduced rates of red blood cell production, and increased body mass relative to controls. We detected no effect of infection on oxidative damage, two metrics of the immune response, or circulating glucocorticoid concentrations. Our results suggest the physiological costs of malaria infection can be substantial and could relate to the cost of replacing red blood cells damaged during infection.
