Sexual harassment causes catfights in guppies

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In fish, as in humans, males may be the reason why some catfights take place, according to a study to be published in a forthcoming issue of the journal Biology Letters.

In their paper, Safi Darden and Lauren Watts demonstrated that the constant sexual harassment caused by the presence of male guppies caused female guppies to become more aggressive towards peers of the same sex.

The authors conducted two series of experiments to test the hypothesis that the presence of male guppies would alter social behaviours expressed by females towards other females in the population.

In the first set of experiments, the authors placed three transparent cylinders spaced equally apart in a tank. They placed two female guppies within each sealed cylinder, and then introduced either a pair of female guppies (one larger than the other, with the larger one serving as the focal female) or a large (focal) female and smaller male guppy into the tank.

The time spent by the focal female swimming near the cylinders (taken to correspond to the time spent shoaling with other females) was recorded in a 10-minute observation period.

In the second set of experiments, the authors stuck fish flakes to a microscope slide using petroleum jelly, and then added six fish in one of two treatments: three average-sized females and three small females in one treatment and three average-sized females and three (small) males in another.

The fish were observed for 15 minutes, during which the actor and recipient of six well-defined aggressive behaviours (nips, nudges, chase, parallel swimming, tail beating and patch dominance) were recorded.

The authors found that the social behaviour of female guppies are strongly affected by the presence of harassing males. In the company of a male, female guppies spent less time shoaling with other female guppies (the female initiated the move from one group to another in the first set of experiments, indicating that it was trying to escape the attentions of the amorous male). They also behaved more aggressively towards other females in a group while foraging at a food patch if males were present.

This is thought to be a case of misdirected aggression by the authors, in which the females take out their frustrations at being sexually harassed by the male on other females.

The authors hypothesise that the change in circulating hormone levels within the female caused by the presence of the males may be a possible mechanism.

For more information, see the paper: Darden, SK and L Watts (2011) Male sexual harassment alters female social behaviour towards other females. Biology Letters doi:10.1098/rsbl.2011.0807

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