Male Bling Makes Female Fish Mature Faster
It's the look of love--when female green swordtail fish see attractive adult males such as this one, they mature faster sexually, researchers now find.
Credit: Craig Walling, University of Exeter

It's the look of love--when female green swordtail fish see attractive adult males, they mature faster sexually, researchers now find.

On the other hand, scientists discovered when young male green swordtails saw attractive adult males, they matured sexually more slowly.

[See fish courtship video.]

This appears to be the first evidence that visual cues can affect the rate of sexual maturation of a species.

"This effect shouldn't be limited to just this one species we studied here," evolutionary ecologist Craig Walling at the University of Exeter told LiveScience.

Walling and his colleagues investigated green swordtail fish, a Central American species popular in the tropical aquarium market. The fish is named after the striking green sword-like ornament males have extending from their tailfins, making themappear larger and more attractive to females.

"They're a very visually oriented species," Walling explained.

The researchers kept juvenile and adult green swordtails in separate tanks so they could see each other through the glass but not use their other senses. Walling and his colleagues discovered young females shown males with long swords reached sexual maturity up to four months faster than females who weren't. At the same time, young males shown adults with impressive swords matured later than others that were shown less attractive adults.

The researchers speculated this effect helps females maximize their chances for quality mates and helps males avoid competition from more attractive males. "You would suspect that physical things like nutrition would have an effect on sexual maturation, so it's very surprising that just visual cues do," Walling said.

Regarding whether or not similar effects might be seen in humans, "humans are becoming sexually mature at earlier ages, but that's most likely due to improvements in nutrition and health, and not to watching too many Johnny Depp or Brad Pitt films," Walling said.

Still, this effect might be seen in other species and could affect conservation of endangered animals, Walling said. "In order to conserve something, it has to be sexually mature, so it's important to understand what contributes to its maturation," he said

Future research could also see whether other visual cues affect sexual maturation, such as the presence of predators.

Walling and his colleagues report their findings this Valentine's Day in the journal Biology Letters.