Gay by mercury

Water contamination may alter white ibises’ hormones

By Pooja Singh
Published: Saturday 15 January 2011

imageMERCURY contamination in Florida’s rivers is turning a bird species homosexual. A study by the University of Florida in the US claimed that exposure to the toxic chemical made male American white ibises mate with other males—a phenomenon unknown in the species. Previous scientific studies focussed on how methylmercury—the most toxic form of mercury—affected fish and other marine species. The five-year study on birds is the first of its kind.

Peter Frederick, professor of wildlife ecology and conservation at the university, and his team started studying the effects of methylmercury on the birds— common to Florida’s wetlands called the Everglades—after noticing reduced breeding. The birds get exposed to methylmercury by feeding on crustaceans and other small invertebrates which absorb the chemical from municipal waste disposed of near the wetlands.

The researchers divided 160 young ibises into four groups of equal numbers of males and females. Three groups were administered low, medium and high doses of methylmercury (between 0.05–0.3 parts per million); a fourth control group was given a chemical-free diet. Once the birds reached sexual maturity, about 55 per cent of the males on high methylmercury diet were found to be nesting with other males, the study published in the December issue of Proceedings of the Royal Society B stated.

Overall, females on the high chemical diet produced 35 per cent fewer fledglings than females in the control group, the study stated. “We knew mercury can disrupt hormones. Most disturbing was that low mercury levels affected mating behaviour,” said Frederick. The mechanism that causes this change in behaviour is not fully understood. But mercury is known to disrupt hormonal signalling, so it could have a direct impact on the sexual behaviour that is mediated by those hormones. “Birds in the embryonic stage seem to be the most sensitive to it,” said Gary Heinz, wildlife researcher at the US Geological Survey.

Frederick pointed out that no inferences should be drawn about human homosexuality based on the study’s results since the drivers of human sexuality are much more complex than that of birds’.

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