GUT PARASITE LEVELS ARE ASSOCIATED WITH SEVERITY OF RESPONSE TO IMMUNE CHALLENGE IN A WILD SONGBIRD.

J Wildl Dis. 2018 Jul 12. doi: 10.7589/2017-07-176. [Epub ahead of print] Vaziri GJ1, Muñoz SA2, Martinsen ES3, Adelman JS1. Author information 1 1   Department of Natural Resource Ecology and Management, Iowa State University, 339 Science Hall II, 2310 Pammel Dr., Ames, Iowa 50010, USA. 2 2   Department of Computational Biology of Infection Research, Helmholtz Centre for Infection Research, Inhoffenstraße 7, 38124 Braunschweig, Germany. 3 3   Center for Conservation Genomics, Smithsonian Conservation Biology Institute, National Zoological Park, PO Box 37012, MRC5503, Washington, DC 20013-7012, USA. Abstract   Life history trade-offs have been posited to shape wild animals' immune responses against microparasites (e.g., bacteria, viruses). However, coinfection with gut helminths may bias immune phenotypes away from inflammatory responses and could be another mechanism underlying variation in immune responses. We examined how the magnitude of a common and costly response to microparasites, the acute phase response (APR), varied with helminth coinfection at both the individual and the population levels in Song Sparrows ( Melospiza melodia). The APR includes fever and sickness behaviors, like lethargy and anorexia, and provides a whole-organism metric of immune activation. We combined data on fever and lethargy in response to an immune challenge (lipopolysaccharide) with postmortem data assessing helminth burdens and data on malarial parasite infection from blood samples in sparrows from two populations: southern California and western Washington, USA. We predicted that birds with higher helminth burdens would express less severe APRs, at both the individual and population levels. Furthermore, we predicted that these reduced immune responses would diminish resistance against malarial parasites and would thus be associated with higher prevalences of such parasites. Previously, Song Sparrows from Washington have been shown to mount less severe APRs than those from California. In our study, Washington birds also exhibited higher helminth burdens and a higher prevalence of one type of avian malarial parasite. Because of low variation in helminth burdens in California (median=0, range=0-3), we tested within-population relationships only in birds from Washington, where the severity of fever and lethargy correlated negatively with helminth burden. These results suggested that helminth coinfection could help mediate immune responsiveness in wild songbirds. KEYWORDS: Acute-phase response; Song Sparrow; fever; helminth; sickness behavior PMID: 29999463 DOI: 10.7589/2017-07-176