Males Exposed to Contamination with Female Sex Hormones Sing Better!

It is known that hormone-mimicking chemicals, dumped into the water, are the cause of a boom in cases of hermaphroditism in fish and frogs. But these chemicals contaminate the soil as well, and eventually this contamination will mostly affect the humans, as they are exposed to these substances.

A new research made at Cardiff University and published in the journal "PLoS One" shows that wild birds consuming invertebrates from soils contaminated with these endocrine disrupting chemicals display both brain and behavioral changes: male birds exposed to estrogen-mimicking chemicals have more complex songs, turning them into the preferred of the females, but this comes at the price of a decreased immunity.

The team led by Katherine Buchanan investigated males of European starlings (Sturnus vulgaris) feeding close to a sewage treatment station, in the south-west UK, and earthworms that made their base diet.

Males consuming earthworms with a complete array of estrogen-mimicking chemicals sang longer, more often and more complex, fact that boosted their sexual success, even if they presented lower immune function.

The effect was connected to the high vocal center (HVC), a brain nucleus related to male song complexity, which appeared to have a larger size in the contaminated birds. Estrogen, even if a female sex hormone, appeared to induce masculinization in the songbird brain and a higher number of estrogen receptors in HVC. It appears that brain anatomy can be shaped by exposure to estrogen-mimicking chemicals or higher estrogen levels, a result that points to a high-degree plasticity of the adult brain, at least in the case of the songbirds.

This research is a first one finding that a mixture of endocrine disrupting chemicals can actually boost reproductive success in contaminated animals.

"This is the first evidence that environmental pollutants not only affect, but paradoxically enhance a signal of male quality such as song. These results may have consequences of population dynamics of an already declining species," said Buchanan.