Journal
CANADIAN JOURNAL OF ZOOLOGY
Volume 93, Issue 1, Pages 21-29Publisher
CANADIAN SCIENCE PUBLISHING
DOI: 10.1139/cjz-2014-0223
Keywords
Agelaius phoeniceus; Red-winged Blackbird; sex differences; parasitism; helminth; ectoparasite; blood parasite; immunocompetence; bacteria-killing ability; diet
Categories
Funding
- Sigma Xi GIAR [G20100315152954]
- University of California Santa Barbara College of Creative Studies Summer Undergraduate Research Fund
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Sex biases in parasitism rates are widely reported in the literature. Among vertebrates in particular, males are more frequently parasitized than females. These sex-linked differences are often attributed to different investment strategies in current versus future reproduction at the ultimate level and to different levels of circulating androgens at the proximate level. But there are other factors that can influence parasitism rates that are often neglected. In this study, we examined multiple measures of parasitism in male and female Red-winged Blackbirds (Agelaius phoeniceus (L., 1766)) to determine whether sex biases occur and sought to identify physiological and ecological factors that may be shaping such differences. We assessed three groups of parasites (ectoparasites, intestinal parasites, blood parasites), one measure of immune function (bacteria-killing ability), and diet. We found that male-biased infections were common only for intestinal parasites, but could not be attributed to dietary or immunological differences. We also found that immune function was associated with an individual's infection status, appearing elevated in males infected with helminths. Our results suggest that, for this species, sex biases in parasitism do occur but are not the norm. Furthermore, their existence may depend on the nature of the host-parasite relationship.
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