Links between blood parasites, blood chemistry, and the survival of nestling American crows. Issue 17 (7th August 2018)

• Record Type: Journal Article
• Authors: Townsend, Andrea K.; Wheeler, Sarah S.; Freund, David; Sehgal, Ravinder N. M.; Boyce, Walter M.
• Is Part Of: Ecology and evolution. Volume 8:Issue 17(2018)
• Page Start: 8779
• Page End: 8790
• Publication Date: 2018-08-07
• Subjects: acute infection -- avian health parameters -- avian malaria -- ecoimmunology -- immunocompetence -- pathogenicity; Ecology -- Periodicals; Evolution -- Periodicals; 577.05
• DOI: 10.1002/ece3.4287
• Languages: English
• ISSNs: 2045-7758

Abstract

Abstract: Many studies have used the avian hemosporidians ( Leucocytozoon, Plasmodium, and Hemoproteus ) to test hypotheses of host–parasite co‐evolution, yet documented health and survival consequences of these blood parasites vary among studies and generalizations about their pathogenicity are debatable. In general, the negative effects of the hemosporidians are likely to be greatest during acute infections of young birds, yet most previous studies in wild passerines have examined chronic effects in adults. Here, we evaluated responses of nestling American crows ( Corvus brachyrhynchos ) to acute infection (prevalence and burden), as well as its short‐ and long‐term survival consequences. We used panel of nine hematological and biochemical parameters that are regularly used to evaluate the health of domestic animals, including leukocyte profiles, hematocrit, and plasma proteins. We assessed the effects of infection on survival in a mark‐recapture framework. Overall, 56% of crows ( n = 321 samples) were infected by at least one of the three genera. Infections by all genera were associated with elevated plasma proteins and globulins, which could indicate an adaptive immune response. However, only Plasmodium infections were associated with low hematocrit (anemia) and lower fledging success, possibly mediated by the negative effect of low hematocrit values on body condition. Moreover, early Plasmodium infection (<40 days of age) had long‐term survival implications: it was associated with lower apparent survival probability within 3 years after fledging. These results suggest that young crows mounted an adaptive immune response to all three genera. Short‐ and long‐term pathological effects, however, were only apparent with Plasmodium infections. Abstract : Avian blood parasites are often used as a model system in studies of host–pathogen interactions and co‐evolution, yet the extent to which they are actually pathogenic is still a subject of debate. Here, we showed that nestling American crows appeared to mount an adaptive immune response to three different genera of blood parasites ( Plasmodium, Leucocytozoon, and Haemoproteus ), but that only Plasmodium appeared pathogenic. Specifically, nestlings infected with Plasmodium had lower hematocrit levels, were in poor condition, had lower fledging success, and had a lower probability of survival within the first three years of life after fledging.