A common belief among club-going men is that women choose less attractive friends to make themselves look better. See this clip from that important anthropological documentary "Hall Pass" for context:



Not so, says a group of scientists who have observed the opposite strategy in the Trinidadian guppy, a species of small freshwater fish  - instead, the uglier friends are choosing the prettier females to avoid unwanted male attention. 

Male guppies are well known for frequent and sometimes constant harassment of females. This puts a significant burden on females, sometimes preventing them finding food and escaping from predators. Females are 'receptive' for a few days in each month. During this time they emit a sexual pheromone that attracts males and allow males to glide into a position that facilitates mating.

The researchers used guppies descended from those living in the Aripo River in Trinidad. They identified which females were currently receptive to male sexual attention and which were not. They then monitored the amount of time both receptive and non-receptive females chose to spend with either receptive or non-receptive females.

They found that non-receptive females spent significantly more time with receptive, and therefore more sexually attractive, females and that, by doing so, they received far less attention from males. In fact, they even chose water in which receptive females had recently swum over water that had housed other non-receptive fish. This shows they picked up on chemical cues emitted by receptive females and found this to create a more appealing social environment.

Lead researcher Dr Safi Darden of the University of Exeter said, "It is now becoming apparent that males of some species choose to associate with relatively less attractive males to increase their chances of mating. We wanted to see if females also chose their same-sex companions based on attractiveness, but in this case, to reduce unwanted attention."

"Our results support the idea that social structure can develop around relative attractiveness and mating strategies. Although we focused our study on one species of fish, I would expect that this strategy would be seen in other species where females face similar levels of unwanted sexual attention from males."

 Published in the journal Proceedings of the Royal Society B.