Compromised immune competence in free-living tree swallows exposed to mercury
- 308 Downloads
Mercury is a pervasive environmental contaminant and a well-documented immunosuppressor. However, little is known about the effects of mercury contamination on health of free-living vertebrate populations. The South River in Virginia, USA was heavily contaminated with industrial mercury from 1929 to 1950, and recent studies have documented high levels of circulating mercury in riparian songbirds breeding below the site of contamination. Here we used two standardized immune assays, mitogen-induced swelling in response to phytohaemagglutinin (PHA) and antibody response to sheep red blood cells (SRBCs), to test for effects of mercury toxicity on the immune system of female tree swallows (Tachycineta bicolor) which feed on terrestrial and aquatic insects along the contaminated waterway. We found that females breeding at mercury-contaminated sites mounted significantly weaker PHA-induced swelling responses than those at reference sites in both years of study. However, among females on the contaminated sites, individual bloodstream mercury concentration did not predict the extent of mitogen-induced swelling. We did not detect any differences between reference and contaminated females in the strength of antibody responses to SRBCs, but sample sizes for this assay were significantly smaller. Overall, our results suggest that mercury toxicity can exert sub-lethal immunosuppression in free-living, insectivorous songbirds. The potential fitness consequences of the detected differences in immunocompetence caused by mercury toxicity warrant further study.
KeywordsMercury Songbird Immune competence Tree swallow Tachycineta bicolor
Funding was provided by E.I. DuPont de Nemours and Company and the Vice Provost for Research at College of William & Mary and NSF UBM 0436318. We thank the South River Science Team, Rebecka Brasso, Anne Condon, Rachel Fovargue, Adrian Monroe, Robert Taylor and the many cooperative landowners in the Shenandoah Valley. Two anonymous reviewers helped to improve the manuscript.
- Day RD, Segars AL, Arendt MD, Lee AM, Peden-Adams MM (2007) Relationship of blood mercury levels to health parameters in the loggerhead sea turtle (Caretta caretta). Environ Health Perspect 115:1421–1428Google Scholar
- Hill CH (1979) Dietary influences on resistance to Salmonella infection in chicks. Fed Proc 38:2129–2133Google Scholar
- Kumar A, Chauhan RS, Singh NP (1999) Immunopathological effect of mercury on humoral immune response in chickens. Indian J Anim Sci 69:550–552Google Scholar
- Robertson RJ, Stutchbury BJ, Cohen RR (1992) Tree Swallow (Tachycineta bicolor). In: Poole A, Stettenheim P, Gill F (eds) The birds of North America, No. 11. The Academy of Natural Sciences, Philadelphia PA, and American Ornithologists’ Union, Washington DCGoogle Scholar
- Spalding MG, Frederick PC, McGill HC, Bouton SN, Richey LJ, Schumacher IM et al (2000) Histologic, neurologic, and immunologic effects of methylmercury in captive great egrets. J Wildl Dis 3:423–435Google Scholar
- Stutchbury BJ, Robertson RJ (1986) A simple trap for catching birds in nest boxes. J Field Ornithol 57:64–65Google Scholar
- Wiener J, Krabbenhoft D, Heinz G, Scheuhammer A (2003) Ecotoxicology of mercury. In: Hoffman D, Rattner BA, Burton GA Jr, Cairns J Jr (eds) Handbook of ecotoxiology. CRC Press, Boca Raton, pp 409–463Google Scholar