Sex differences in mercury contamination of birds: testing multiple hypotheses with meta-analysis.
The sex of a bird can, in principle, affect exposure and accumulation of mercury. One conventional explanation for sex differences in mercury burden suggests female birds should have lower concentrations than conspecific males, because breeding females can depurate methylmercury to their eggs. However, sex differences in body burden of mercury among birds are not consistent. We used meta-analysis to synthesize 123 male-female comparisons of mercury burden from 50 studies. For breeding birds, males had higher concentrations of mercury than did females, supporting egg depuration as a mechanism. However, the percentage of female body mass represented by a clutch did not significantly predict the magnitude of the sex difference in mercury contamination, as predicted. Furthermore, whether species were semialtrical or altrical versus semiprecocial or precocial also did not explain sex differences in mercury burden. Foraging guild of a species did explain near significant variation in sex differences in mercury burden where piscivores and invertivores showed significant sex differences, but sex differences were not detected for carnivores, herbivores, insectivores, and omnivores. The magnitude and direction of sexual size dimorphism did not explain variation in sex differences in mercury burden among breeding birds. We reveal targeted research directions on mechanisms for sex differences in mercury and confirm that sex is important to consider for environmental risk assessments based on breeding birds.
Department of Biology, Carleton University, 209 Nesbitt Building, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada. srobinsc@connect.carleton.ca
Stacey A
SA
Robinson
Marc J
MJ
Lajeunesse
Mark R
MR
Forbes
D000818:Animals; D001717:Birds / Q000502:physiology*; D049628:Body Size; D004531:Eggs / Q000032:analysis; D004784:Environmental Monitoring; D004785:Environmental Pollutants / Q000032:analysis* / Q000378:metabolism; D005247:Feeding Behavior; D005260:Female; D008297:Male; D008628:Mercury / Q000032:analysis* / Q000378:metabolism; D012737:Sex Factors
D004785:Environmental Pollutants; D008628:Mercury