The ecology of host immune responses to chronic avian haemosporidian infection
Host responses to parasitism in the wild are often studied in the context of single host–parasite systems, which provide little insight into the ecological dynamics of host–parasite interactions within a community. Here we characterized immune system responses to mostly low-intensity, chronic infection by haemosporidian parasites in a sample of 424 individuals of 22 avian host species from the same local assemblage in the Missouri Ozarks. Two types of white blood cells (heterophils and lymphocytes) were elevated in infected individuals across species, as was the acute-phase protein haptoglobin, which is associated with inflammatory immune responses. Linear discriminant analysis indicated that individuals infected by haemosporidians occupied a subset of the overall white blood cell multivariate space that was also occupied by uninfected individuals, suggesting that these latter individuals might have harbored other pathogens or that parasites more readily infect individuals with a specific white blood cell profile. DNA sequence-defined lineages of haemosporidian parasites were sparsely distributed across the assemblage of hosts. In one well-sampled host species, the red-eyed vireo (Vireo olivaceus), heterophils were significantly elevated in individuals infected with one but not another of two common parasite lineages. Another well-sampled host, the yellow-breasted chat (Icteria virens), exhibited no differences in immune response to different haemosporidian lineages. Our results indicate that while immune responses to infection may be generalized across host species, parasite-specific immune responses may also occur.
KeywordsAvian malaria Ecoimmunology Haemosporida Haptoglobin Leukocytes
Alicia Burke, Kristen Bird, Elyse Coffey, Linlin Meng, and William Burke assisted with fieldwork and Eloisa Sari provided advice regarding lab procedures and insightful comments on an earlier version of the manuscript; Iris Levin, Matthew Medeiros, Eliot Miller, Michael Collins, Alix Matthews, Alison Hanson, Jackson Roberts and an anonymous reviewer also provided helpful comments. The Whitney Harris World Ecology Center at UMSL funded this project through the Leo and Kay Drey Scholarship (V. A. E.). The Missouri Department of Conservation provided housing and logistical support. Logistics were also facilitated by John Faaborg. Laboratory funds were provided by the Curators of the University of Missouri (R. E. R.). All sampling occurred under appropriate federal and state permits and in accordance with the UMSL IACUC.
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