Female intuition picks the strong from the weak

By:AAP with Natsumi Penberthy | January-11-2012

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Female fish can discern mates that were malnourished or well fed in youth, even if they look the same as adults.

A male mosquitofish is favoured by a large female, while another gets the cold shoulder. (Credit: Andrew Kahn)

BEING WELL FED as a kid can make you more attractive to females - if you are a mosquitofish, that is.

Researchers from The Australian National University (ANU) have shown that female mosquitofish (Gambusia holbrooki) prefer males who had a solid nutritional upbringing, even if the males are superficially identical to their poorly-fed brothers. Their findings are published online today in the journal Biology Letters.

"Males similar in body size, but differing in developmental history, are not equally attractive to females," says Andrew Kahn, the study's lead author and a PhD candidate at ANU's Research School of Biology in Canberra.

Mosquitofish are an invasive species in Australia, originally introduced to control mosquitoes, although it has since been discovered that they only eat mosquito larvae when there are no other native larvae to eat.

Delaying sexual maturation

Jules Livingston, an ANU honours student and co-author of the paper, previously showed that juvenile mosquitofish born into a food-scarce environment will undergo accelerated growth when food becomes available and delay sexual maturation to catch up with well-fed males of the same age.

In this study, Andrew and his colleagues investigated how this bump in the road to development affected adult mating.

"We gave female fish a choice between two full brothers who were born on the same day: one brother grew normally and the other had a period of poor nutrition and compensated for it by accelerating growth and delaying maturation," he says. "The really interesting thing was that the females seemed to be able to tell the difference between them and preferred those that had undergone normal growth."

Green swordtails which are from the same family of fish, are more dominant if they develop normally, says Andrew, who speculates that this might be one way females identify well-fed males.

Two-fold benefits

"However [unlike green swordtails] there is no active courtship between male and female mosquitofish, it's more a matter of time and place," he told Australian Geographic. "The females just seem to like hanging out with the well-fed males more."

Although the way that female mosquitofish are able to detect which males have undergone compensatory growth is still unclear, Andrew says the attraction of a well-fed male is two-fold.

"If males have undergone a period of poor nutrition they might be more susceptible to diseases which they could then pass on to the female. And there are the indirect genetic reasons - by choosing males who have had a better development history, your offspring have a good chance of being better at getting food when they are young."

"This work demonstrates there are hidden costs to a poor start in life," he says.