Unexpected discovery: Contraceptive residue made male fish aggressive – and worse fathers
A lake experiment in Canada revealed unexpected effects of hormone pollution. The males became more aggressive and showed less ability to protect their eggs. The results are the opposite of what lab tests have shown, according to a study in which a SLU researcher took part.
– The study shows just how complex and unpredictable the effects of chemical pollution are on wildlife, and that the risks may be bigger than those we see in laboratory studies. Thanks to the experiment in the lake, we observed consequences that we might otherwise have missed, says Erin McCallum, researcher at SLU who led the study alongside Karen Kidd from McMaster University and Paul Blanchfield from Fisheries and Oceans Canada.
Residues of medicines reach lakes and rivers via sewage treatment works. The researchers studied the effects of ethinyl oestradiol (EE2), a commonly occurring synthetic oestrogen used in contraceptive pills and other hormone therapies. Over a study spanning 12 years, male fathead minnows were monitored in a lake in Canada before, during and after being exposed to small concentrations of EE2. The researchers compared them with males of the same species in other lakes where the substance was not present. It is known that the hormone can affect male reproduction, and in the study the researchers focused on the fish’s movements and behaviour.
Male fathead minnows normally establish territories, court females and guard the eggs in the nest. Laboratory tests showed that exposure to EE2 made the males less aggressive, but in the natural environment, more fish crowded around the nests, which increased competition, and the males spent more time aggressively defending their territory than tending to the eggs.
– This is a great example of how animals can respond differently in the real world than they do in laboratory experiments. When fish are living in a natural environment, their behaviour is influenced by competition and social interactions that are difficult or impossible to recreate in the lab, explains Karen Kidd, Professor of Biology at McMaster University in Canada and one of the coauthors.
The population collapsed
The researchers observed that EE2 altered the social dynamics, which had major consequences. The increased competition between the males, combined with fewer eggs – which the males also cared for less effectively – likely contributed to the species population collapse that was observed during the experiment.
– The hormone didn’t just affect individual fish. It changed the social conditions in the lake. Those changes had ripple effects on reproduction across the population, says Erin McCallum.
Many environmental studies are carried out under controlled laboratory conditions. The results of this study suggest that the ecological risks posed by residues from hormonal medicines are underestimated.
– The study provides valuable insights into pharmaceutical pollution, which is a globally widespread environmental problem. We hope that our findings can help to improve risk assessments and strengthen efforts to protect our waters, says Erin McCallum.
Scientific article
Current biology: Whole-lake exposure to a widespread estrogenic pollutant leads to unanticipated reproductive behaviors in wild fish Erin S. McCallum, Karen A. Kidd, Andrew R. Majewski, Paul J. Blanchfield.
Press release from McMaster University.
Contact
Erin McCallum, Researcher, Department of Wildlife, Fish, and Environmental Studies, SLU. erin.mccallum@slu.se
Frida Wengberg, Communications officer
frida.wengberg@slu.se +46725669778