title: Direct and indirect causes of sex differences in mercury concentrations and parasitic infections in a marine bird.
abstract: In many animal species, males and females differ in their levels of contaminants and/or parasitic infections. Most contaminants and gastro-intestinal parasites are obtained through prey ingestion, and thus the causes of sex differences in the distribution of these factors might follow similar pathways. We studied the northern common eider duck (Somateria molissima borealis) as an avian model, and used directed separation path analysis to explore the causes of sex differences in mercury (Hg) and gastro-intestinal helminths. Two trophically transmitted helminths were examined: a cestode (Lateriporus sp.) and an acanthocephalan (Polymorphus sp). We found that the number of Lateriporus sp. varied positively with stable isotope signature (as indicated by δ(15)N in eider breast muscle tissue), and negatively with crustaceans being present in the short term diet. We also found that Polymorphus sp. varied positively with eider tissue stable isotope signature. However, Polymorphus sp. varied negatively with sex indirectly through condition and liver mass. Similarly, Hg concentrations also varied negatively with sex indirectly through condition and liver mass, with both Polymorphus sp. intensity and Hg concentrations significantly higher in males. We found that model fit increased when a negative relationship between the two helminth species was included, suggesting a yet unknown causal mechanism linking these parasites. Our findings suggest that although Hg and gastro-intestinal parasites are both trophically transmitted through the eider's prey items, the factors that contribute towards bioaccumulation of these two burdens differ in source, likely caused by several different factors and may potentially influence each other.
authors.affiliation: Department of Biology, Carleton University, 1125 Colonel By Drive, Raven Road, Ottawa, ON K1A 0H3, Canada. Electronic address: jennifpro@gmail.com.
authors.forename: J F
authors.initials: JF
authors.lastname: Provencher
authors.affiliation: Wildlife Research Division, National Wildlife Research Centre, Environment and Climate Change Canada, 1125 Colonel By Drive, Raven Road, Ottawa, ON K1A 0H3, Canada.
authors.forename: H G
authors.initials: HG
authors.lastname: Gilchrist
authors.affiliation: Department of Biology, Acadia University, 33 Westwood Ave, Wolfville, NS B4P 2R6, Canada.
authors.forename: M L
authors.initials: ML
authors.lastname: Mallory
authors.affiliation: Wildlife Research Division, National Wildlife Research Centre, Environment and Climate Change Canada, 1125 Colonel By Drive, Raven Road, Ottawa, ON K1A 0H3, Canada.
authors.forename: G W
authors.initials: GW
authors.lastname: Mitchell
authors.affiliation: Department of Biology, Carleton University, 1125 Colonel By Drive, Raven Road, Ottawa, ON K1A 0H3, Canada.
authors.forename: M R
authors.initials: MR
authors.lastname: Forbes
mesh_terms: D000818:Animals; D046090:Anseriformes / Q000378:metabolism* / Q000469:parasitology; D004781:Environmental Exposure / Q000706:statistics & numerical data*; D005260:Female; D020387:Food Chain; D006376:Helminths; D007411:Intestinal Diseases, Parasitic / Q000453:epidemiology*; D008297:Male; D008628:Mercury / Q000378:metabolism*; D012737:Sex Factors; D014874:Water Pollutants, Chemical / Q000378:metabolism*
chemical_list: D014874:Water Pollutants, Chemical; D008628:Mercury
keywords: Condition; Cumulative effects; Diet; Parasitism; Sex bias; Stressors