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Gay_FishGay behaviour among male fish may increase their chances of scoring a female, according to new research from researchers at the University of Frankfurt.

It could help explain why homosexual behaviours are found in almost every species alive, even though they don’t result in offspring.

Many characteristics and behaviours of today all come from evolutionary advantages that helped that species’ early ancestors survive, the researchers say. For example, the reason we love junk food today is because our ancestors needed high calorie foods (like fatty and sugary candies and chips) to keep our bodies and brains running until their next meal, which was often hard to come by.

Gay behaviour is often seen as an evolutionary disadvantage, because it doesn’t result in reproduction and uses up energy that could be used in passing on genes to offspring. But, mysteriously, gay behaviour is still present in many species from mammals like humans to birds, including ducks, and even in fish.

Specifically, in this case, small males of the Atlantic molly species are often caught copulating with each other. In a new study, published today, Dec. 11 in the journal Biology Letters, researchers set out to find if these homosexual behaviours hold any evolutionary advantages.

The males in this species of fish are either large and colourful, or small and less colourful. The researchers showed female fish video animations of two males, a large one and one that was 50% smaller and 50% less colourful. They found that the females prefer the bigger, more colourful fish.

They then performed a second set of tests where they showed the females animations of the two types of males in several situations, where one type of male (the bigger or smaller fish) would be mating with a male, a female, or not mating.

Interestingly the females were more attracted to males they saw sexually interacting with other fish, a behaviour called mate choice copying. There is value in watching their partner mate, the researchers said, because they can evaluate their reproductive capabilities and suitability as a partner.

In the tests, though, they noticed this increased attraction even if their potential mate was mating with another male. It could be that the smaller, less attractive males are using this to their advantage, by performing homosexual behaviours to increase their attractiveness and their chance of mating with females.

Exclusively gay males are only seen in humans, sheep, and some bird species, but bisexuality is very common in species that live in groups. This study suggests one potential evolutionary advantage of bisexuality — increased attractiveness.

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