Cow steroid pollutants in waterways disrupt the mating habits of female fish, study finds
An international study led by the Monash School of Biological Sciences has found that female fish are less interested in sex if they have been exposed to environmental contaminants associated with livestock production.
The study – a world first – was carried out in Associate Professor Bob Wong’s lab, which focuses on the evolution of animal mating systems and behaviour.
One of the most potent agricultural contaminants in our waterways is 17b-trenbolone, a metabolite of trenbolone acetate, which is a commonly used steroid found in hormonal growth promotants. These are administered to cattle to bolster meat production around the world.
“17b-trenbolone is a known endocrine disruptor, which means it can interfere with the natural hormonal functioning of organisms at disturbingly low concentrations,” said the study’s lead author, Mr Patrick Tomkins, a PhD candidate in Associate Professor Wong’s lab. 
Pollutants disrupt female fish sex life. Credit: Pierson Hill
“Previous studies have examined the impact of this steroid on the mating behaviour of male fish,” Mr Tomkins said.
The researchers focused on female mate choice and what happens when females encounter potential mates sequentially.
“We found that females exposed to 17b-trenbolone were being turned off sex and were spending less time associating with males – regardless of how attractive the males might be,” said Mr Tomkins.
“We also discovered that although exposed and unexposed females were both indiscriminate when they were first presented with a male, unexposed females became more discerning when encountering future males and spent less time with less attractive suitors.”
“Exposed females, by contrast, remained indiscriminate.”
So why should this matter?
Mate choice is important because it can affect both the quality and the quantity of offspring that are produced.
“Indeed, by being choosy, discerning individuals can benefit in a range of ways,” said Associate Professor Wong.
“For example, they might select a mating partner who will be genetically compatible or who will confer 'good' genes to her offspring, or she may end up mating with a suitor that can provide resources to her or her offspring,” he said.
“Processes that disturb mate choice can have important ecological consequences through reduced offspring quality or quantity.”
Previous research has shown that exposure to pollutants can affect female choosiness but it has always been in situations where females are presented with two or more males simultaneously.
“However, in nature, individuals typically encounter potential mates one at a time so it is important to be able to decide whether a particular suitor is a good mating partner or not – or whether it's better to wait until someone better comes along,” Associate Professor Wong said.
The study was published in Environmental Pollution.
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