Female guppies being sexually harassed by their male counterparts

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In a report that shed light on the male-evading tactics of female guppies, researchers have revealed that to escape the sexual harassment, female guppies get better at swimming.

Sexual reproduction in the animal world is all about males enticing the females through either their physique or looks or even force. Male behaviour is driven by conflicts of interest over reproduction and exerts selective pressures on both sexes.

Many a times, when the males become over-competitive, males of many species will try to overcome their competition by using a number of behaviours, such as chasing and even attacking females in an attempt to gain a mating.

Dr Shaun Killen, of the University of Glasgow, said: “Sexual coercion of females by males is widespread across sexually reproducing species.”

Tactics such as chasing are often deemed as harassment in the animal world as well, found researchers of a new study, and researchers say females can spend a lot of energy avoiding males in these situations and can even be injured.

The study by researchers at universities of Glasgow and Exeter on guppies has given scientists insight into how this behaviour can lead to physiological changes, much like those in athletes who train to perform better.

“To reduce these costs, one possibility is that females may be able to change their own behaviour or physiology in ways that reduce the negative energetic consequences of harassment or allows them to more easily escape male coercion”, Killen notes.

For their study, researchers tested this idea in a laboratory setting by exposing female Trinidadian guppies (Poecilia reticulata) for several months to varying levels of male harassment that they would normally encounter in the wild.

Female Guppies Become Better Swimmers to Escape Male Sexual Harassment

This image shows a female and two male guppies (Poecilia reticulata) from the Arima River, Trinidad. Credit: Photo by Darren P. Croft, University of Exeter UK

Researchers say that in their natural habitat, male guppies spend most of their time courting and coercing females in an attempt to mate with them. Most of this male attention is unwanted and females attempt to avoid males by rapidly swimming away from them during pursuits.

The study authors note that after five months, females exposed to higher levels of harassment were able to swim much more efficiently, using less energy to swim at a given speed compared to those exposed to lower levels of harassment.

This means that prolonged increases in high-intensity swimming in females, caused by male harassment, leads to changes in the physiology or swimming mechanics of individual fish, which reduces the energy costs of swimming and could allow female guppies to reduce the burden of this coercive behaviour.

Dr Killen added: “An important factor appears to be swimming technique, and female guppies that experienced lower levels of harassment spent more time swimming with their pectoral fins extended, an indicator of an inefficient swimming technique.

“This change is very similar to that seen in human athletes who train to become better at their sports.”