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After mating, the male releases a sperm packet and attaches it to the female katydid's rear end, along with a cheesy, edible gift squeezed out of his own abdomen. While she is eating, the sperm packet acts as a turkey baster and injects her with sperm. (University of Toronto Mississauga)

Female katydids get macho and may duke it out over an eligible male if they expect him to provide a particularly sumptuous dinner on their subsequent "date," scientists have found.

Typically, females of the cricket-like green insects, like most other females in the animal kingdom, are less willing than males to exert a substantial amount of energy in the hunt for a mate.

Darryl Gwynne, an ecology and evolutionary biology researcher at the University of Toronto Mississauga, was interested in exploring what factors caused the sex roles to reverse in some species.

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Darryl Gwynne talks to Quirks & Quarks on CBC Radio One.

He and his collaborators, led by Jay McCartney at Massey University in New Zealand, predicted that it had to do with the size of an edible gift presented by the male katydids to females after mating.

"It looks for all the world like a big blob of mozzarella cheese on a pizza," Gwynne said of the gift squeezed out by the male from a special gland in his abdomen.

The size of the gift varies from four per cent of the male's body mass to a whopping 40 per cent.

"It's enormous and takes her sometimes several hours to eat her way through it," he told CBC's Quirks & Quarks in an interview set to air Saturday.

As predicted, the researchers found that the larger the gift, the more likely it was that the usual sex roles were reversed among male and female katydids.

"Females will actually fight with each other, compete with each other for access to a male that can produce this," Gwynne said, "and the males sit back and become very female-like in the sense that they become very, very choosy."

The researchers aren't sure how the females figure out which males will provide a big gift, but they think there may be clues in the song that males sing to attract females.

Gwynne said the females don't get to see the gift before mating because it isn't produced until the male releases a sperm packet and attaches it near the female's rear end after mating. The "packet" acts like a turkey baster, injecting the sperm into the female after mating, while she is busy eating the dinner provided by her mate.

"If he doesn't give some sort of gift, she simply reaches around and grabs the turkey baster, which is in itself, a little proteinaceous snack," Gwynne said, " and eats it along with the sperm."

He added that from an evolutionary perspective, the male ultimately benefits from providing the gift because it will go toward nourishing his offspring.

The findings support a general evolutionary theory that even though females don't usually search for males, they will do so if the males offer far more than just sperm.

The results of the study were published in the journal Proceedings of the Royal Society B.