News in Science

Ugly friends lift male's mating chances

Male guppies strategically decide to hang out with ugly friends to increase their chances of picking up, a new study shows.

In a paper published in Proceedings of the Royal Society B Dr Clelia Gasparini, at the University of Western Australia, gives the first explicit evidence that less-attractive male guppies learn through experience that hanging out with the "ugly" crowd can boost their mating success.

For the study, Gasparini and colleagues from the University of Padova in Italy, studied the guppy Poecilia reticulata - a small, colourful fish in which female preference for ornate males is known to control mating.

In a series of experiments, the researchers put a male guppy in a tank and allowed it to choose between two females. One female was surrounded by colourful males, with orange markings covering more than 20 per cent of their body, the other by drab males with less than 9 per cent orange colouration.

The less colourful a male was, the more he gravitated to his drab companions, Gasparini says. Their preference was expressed as the number of times the male approached a female's 'choice' zone.

"Males preferred the female surrounded by drab males," says Gasparini.

"Choosing to associate with relatively dull companions increased their relative attractiveness to the female."

The evolutionary biologist says when the females were removed, males showed no preference for either drab or colourful males, discounting aggression as a potential cause for the behaviour.

Evolutionary enigma

Guppies are one of the few fish with internal fertilisation.

"Most fish reproduce by the female shedding eggs into the water and the male shedding sperm at the same time," says Gasparini. "Male poeciliid fish like guppies have an organ called a gonopodium, a modified fin that transfers sperm along a channel into the female's genital tract.

"Males deposit more or less sperm depending on the female's willingness to continue copulating with them" - or until her attention is caught by a more flashy suitor.

"But if females are always choosing to mate with the most colourful male, then we would expect drab males to disappear from the population," says Gasparini. "It has been an enigma for evolutionary biologists.

"The results of this study help us understand: if drab males choose the right context they will appear attractive to females.

"If you're already a colourful male the context is less important, but if you're drab being near even-duller males increases your chances of being chosen by a female."

Practice makes perfect

So how do males know how attractive they are? It all comes down to experience, says Gasparini.

The team ran the experiment both with 'experienced' males - those that had grown up in a stock tank with 1:1 sex ratios and were allowed to interact freely with both sexes - and 'naïve' males. These were raised only with females, to maintain normal sexual activity during development, but had no visual or physical interaction with other males.

"In the study, naïve males showed no preference for females surrounded by either drab or colourful males, while experienced males' preferences were clear," says Gasparini.

"This shows that they learn to choose the right context through experience, and by observing other males and their successful strategies."