Melbourne: For a male tree weta, size really is everything. In six of the seven species in New Zealand, the males sport a distinctly large head and the bigger the head, the better the chance of mating.
A team at Massey University, led by Dr Cilla Wehi, says it has found that, despite their size, males are at no greater risk of being spotted and attacked by predators than females.
"Having the big head is a plus in terms of getting and guarding females. The big head means a male has a larger mandible that helps win the battles with other males for control of females.
"But it also means that adult males are conspicuous, as they come out at night to feed and fight," Wehi said.
The downside, according to theory, is that there should be some disadvantage, such as higher predation because adult males are out in the open being more active and visible.
"So are they more likely to be snapped up by a morepork or a rat, for example?"
Dr Wehi and her colleagues wanted to test this theory of sex-biased predation to see whether it was evident.
They looked at the sex ratios in different populations to see if the numbers of adult males and females were the same.
"If there were more females than males, then we would know that there is a cost to having that big head," she said.
They gathered data from all around the country covering 58 populations, and surprisingly found there wasn't a higher predation rate in males. "So we've found something quite different from what theory predicts. It turns theory upside down," she said.
PTI
First Published: Saturday, November 19, 2011, 13:00