This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A team of researchers has found that a common wastewater pollutant turned male fathead minnows into worse fathers and fiercer rivals, revealing ecological impacts that laboratory studies missed. The pollutant, called ethinylestradiol (EE2), is a synthetic estrogen used in oral contraceptives and other hormone therapies.
While municipal wastewater treatment removes much of the compound, small but potent amounts still enter rivers and lakes. Scientists have long known it can affect fish reproduction. What remained unclear was whether it could also alter fish behaviors that are critical for population survival.
While laboratory studies suggested that exposure to EE2 would reduce aggression in male fish, researchers studying an entire lake ecosystem found the opposite. Researchers observed more fish around active nests, increasing competition and causing nesting males to spend more time defending territories and eggs. "This is a great example of how animals can respond differently in the real world than they do in laboratory experiments," explains Karen Kidd, a professor in the Department of Biology.
"When fish are living in a natural environment, their behavior is influenced by competition and social interactions that are difficult or impossible to recreate in the lab." To better understand the hormone's effects in a natural setting, researchers conducted a whole-lake experiment, monitoring male fathead minnows before, during and after a three-year period during which trace amounts of EE2 were added to an experimental lake. They compared the fish with populations living in nearby lakes that were not exposed. The researchers found that EE2 changed the social dynamics of the fish population.
Male fathead minnows normally establish territories, court females and guard the eggs laid in their nests. During the exposure period, competition around active nests increased. The added rivalry, combined with reduced parental care and fewer eggs in nests, likely contributed to the population collapse observed during the experiment.
These results are published in the journal Current Biology. "The hormone didn't just affect individual fish. It changed the social conditions in the lake.
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