Meeting Abstract
Infectious diseases are spreading at unprecedented rates, reducing the abundance, distribution, and/or long-term viability of many wild animals. Avian malaria has recently contributed to the decline of several endemic Hawaiian birds. Fortunately, some populations of the native Hawaii Amakihi (Hemignathus virens) display tolerance to the disease. We sought to experimentally determine the effect of corticosterone (CORT), an immunosuppressor, on immune function and malaria infection in wild Amakihi. Based on our field data, which show reduced CORT increase in response to capture and restraint stress in tolerant versus susceptible populations, we hypothesized that variation in circulating CORT influences malaria tolerance. To test this, we studied 40 captive adult males from tolerant and susceptible populations, implanting each with a CORT (n = 20) or sham (n = 20) silastic implant for 4 days and measuring immune function and malaria infection on day 0 (before implant), 2, and 4. CORT levels were higher on day 2 and 4 in CORT than sham birds, with no effect of tolerance status. On day 2, total leukocyte count was elevated in susceptible but not tolerant CORT-implant males compared to sham-implant males, while no differences by tolerance status were detected on day 0 or 4. Hematocrit decreased more during the experimental period in CORT-implant than sham-implant birds with no effect of tolerance status. Our results suggest that immune response may be less influenced by increased CORT in malaria-tolerant than malaria-susceptible birds.
