Thanks to Human Evolution! Males Prevented from Walking for Sex!

by VR Sreeraman on Sep 7 2008 10:00 AM

Male giant wetas walk a considerable distance each night for sex, and their lightweight and longer legs help them satiate their wanderlust, according to a field study on Maud Island, New Zealand.

Studying the flightless and nocturnal Cook Strait giant weta Deinacrida rugosa, evolutionary biologists from the University of Toronto at Mississauga have found that males can walk more than 90 m each night in search of a mate, which is roughly equivalent to a 7000 m outing by a human male.

Deinacrida rugosa is a relative of the cricket, and is found in New Zealand. It is one of the world's heaviest insects with females weighing in at 20g, averaging twice the size of males.

Study leaders Luc Bussiere, and Darryl Gwynne found that male giant weta most successful at mating travelled greater distances each night.

The researchers revealed that they gained unprecedented insight into mating habits of weta by radio-tracking them over several days, which enabled them to calculate how much distance the insects walked, and with whom each male and female "spent the day".

As a male giant weta copulates repeatedly with his mate throughout the day, said the team, they also estimated how much sperm was transferred by counting the empty packets (spermatophores) piled beneath the pair.

The researchers said that not found that not only did the males travel more than twice as far as the females, but they also walked further, acquired more mates, and transferred more spermatophores to females.

"Our findings are a rare example of sexual selection favoring a suite of traits that promote greater mobility in one sex only," stated Kelly, adding " this is exciting because it suggests that sexual selection for smaller, more mobile males could be responsible for some of the impressive sexual difference in body size in this species."

The researchers believe that their work may help understand why males are smaller than females in some other animals.

The study has been published in the journal The American Naturalist.