Recent research shows that Trinidadian guppies display female-against-female aggression in the presence of a harassing male.
Like humans, female guppies produce few eggs and keep them inside their bodies for males to fertilize. Because guppy fertilization does not depend on seasons, female guppies must work continuously to avoid unwelcome attention from males.
During mating season, male guppies either attract females with their brightly-colored bodies or harass smaller females into mating by nipping and chasing them. The females usually only mate with the most attractive males to ensure the production of high-quality offspring. If the male is rejected, he will often attempt to mate with the female of his choice when she is not looking.
In an attempt to avoid the harassing male, the female gives up precious time and energy for foraging, growth and reproduction. As a result, she may spend more time in areas with high concentrations of predators in an attempt to avoid the males. The brightly-colored males avoid these areas, as they are more likely to attract the predators compared to the dull-colored males.
In addition to encouraging risky behaviors, the presence of a harassing male also disrupts female social networks and facilitates female-on-female aggression. According to Safi-Kristine Darden of the University of Exeter in southwestern England, aggression can be a good indicator of how a female's opportunities for bonding could be affected. However, the amount of time females have to familiarize with one another and establish dominance hierarchies diminishes due to harassment from males.
Guppies, which constantly move between social groups in the water, form female pairs that help them improve foraging and protect them from predators. To illustrate how harassment affects these female social bonds, the researchers placed three pairs of guppies, which were a random mix of females and smaller males, into a transparent cylinder. They then introduced either a pair of female guppies or a male and a female guppy into a larger tank immediately outside the cylinder.
The researchers found that, when paired with a male, the female in the larger tank spent less time with each group and moved more frequently from one cylinder to another. As the female, rather than the male, initiated the move between groups, it was likely that the female was trying to escape from the aggressive male.
When females are in the presence of an aggressive male, they have less time to spend with other females, probably because they are trying to escape from the male, Darden says.
The researchers also examined how the presence of a harassing male can cause aggressive behaviors in all-female or mixed-sex groups. To test this, they added a food patch to the area and observed how the female guppies competed over the food.
In mixed-sex groups, females used nips, nudges, chasing and tail beatings to deter other females from approaching. According to Darden, the guppies were directing these aggressive acts towards other large females. In addition, the level of aggression was much higher when male guppies were present.
The research team believes that these behaviors may be a case of misplaced aggression. Unable to do anything about the harassing male, the females vent by taking out their frustration on neighboring females. It is possible that male hormones in the water, or pheromone communication between the fish, are causing these behaviors.
