Sex and Evolution: Female Guppies Speed-Swim to Avoid Males

Female guppies speed up their swimming technique in order to leave behind sexually harassing male guppies.

That is, a recent study by the universities of Glasgow and Exeter discovered that female guppies experience a change in physiological behavior when being courted by their male counterparts, causing them to swim faster to avoid unwanted harassment. Over the course of several months, researchers exposed female Trinidadian guppies (Poecilia reticulata) to varying levels of male harassment that they would normally encounter in the wild, said a release. 

"Typically, male reproductive success is limited by access to females, and males of many species will try to overcome this using a number of behaviors, such as chasing and even attacking females in an attempt to gain a mating," Dr. Shaun Killen, of the University of Glasgow, said in a statement. "Sexual coercion of females by males is widespread across sexually reproducing species."

Since the female guppies may not be initially interested in the male guppies, Killen further explains in the statement, "These types of behaviors are considered sexually harassing as males are attempting to coerce females into mating with them. Females can spend a lot of energy avoiding males in these situations and can even be injured. To reduce these costs, one possibility is that females may be able to change their own behavior or physiology in ways that reduce the negative energetic consequences of harassment or allows them to more easily escape male coercion."

According to their study, after five months of being exposed to higher levels of harassment, females were able to swim much more efficiently, thus using less energy compared to those exposed to lower levels of harassment. Their research has recently been published in the journal, Functional Ecology.

"It seems 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 behavior," Dr. Safi Darden of the University of Exeter said in the statement. 

"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," Dr. Killen added in the release. "This change is very similar to that seen in human athletes who train to become better at their sports." 

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