Size doesn’t matter in insect sexSeptember 6th, 2008 - 2:01 pm ICT by IANS
Toronto, Sep 6 (IANS) When it comes to sex, an insect species has shown size doesn’t really matter, but it involves tremendous legwork on the part of the much smaller, lighter males to bring it off.The species is the flightless, nocturnal Cook Strait giant weta male, a close kin of crickets, native to New Zealand, counted among the world’s heaviest insect groups.
Male specimens that walked the longest distance had the greatest success in their mating quest. Of course, being half the size of females was compensated by longer legs that helped them in their nocturnal wanderlust.
Evolutionary biologists from the University of Toronto at Mississauga - Clint Kelly, Luc Bussière, and Darryl Gwynne - found that males can walk more than 90 metres each night in search of a mate, roughly equivalent to a seven km outing in human terms.
Kelly and colleagues gained unprecedented insight into mating habits of weta by radio-tracking them over several days. This allowed calculations of distance walked and identification of the insects with whom each male and female “spent the day”.
Because a male giant weta copulates repeatedly with his mate throughout the day, the biologists estimated how much sperm was transferred by counting the empty packets (spermatophores) piled beneath the pair.
Not only do males travel more than twice as far as females but small, long-legged individuals walked further, acquired more mates, and transferred more spermatophores to females. No female traits predicted female mobility or mating success.
“Our findings are a rare example of sexual selection favouring 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”.
Importantly, however, this phenomenon may also help to explain why males are smaller than females in some other animals.
The findings were published in the September issue of The American Naturalist.