For male weta, big is better

November 18, 2011
Dr Cilla Wehi with a male tree weta.

(PhysOrg.com) -- For a male tree weta, size really is everything. In six of the seven species in New Zealand the males all sport a distinctly large head, and the bigger the head, the better the chance of mating.

Massey University post-doctoral researcher Dr Cilla Wehi has been studying whether there is a downside to this evolutionary feature.

But she found that, despite their size, males are at no greater risk of being spotted and attacked by than .

“Having the big head is a plus in terms of getting and guarding females,” she says. “The big head means a male has a larger mandible that helps win the battles with other males for control of females,” she says. “But it also means that adult males are conspicuous, as they come out at night to feed and fight.”

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?”

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Dr Wehi and her colleagues wanted to test this theory of sex-biased predation to see whether it was evident.

Dr Wehi 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.”

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.”

However, Dr Wehi says there must be some cost, otherwise the size of male weta heads would just keep getting bigger and bigger. More work is needed to identify what that cost is.

Dr Wehi worked with colleagues in Massey’s Ecology group, including Dr Mary Morgan-Richards and Dr Steve Trewick. The paper was published in the Journal of Evolutionary Biology.

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9 comments

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rynox
1 / 5 (1) Nov 18, 2011
It's not the size of your weta, it's how you use it.
Callippo
1 / 5 (3) Nov 18, 2011
She was nearly eaten alive with this male during her lecture.. An example of sex-biased predation.
Humpty
1.8 / 5 (5) Nov 18, 2011
I wonder IF the jaws really are - like if your another cricket or something, being bitten by them looks to be a bad deal, but can these actually bite through the skin and slice the flesh open...

OH the video... she is not screaming or flinching, OK it bites.. and they can draw blood...

Just not needing stitches that is all.
sherriffwoody
not rated yet Nov 19, 2011
It's not the size of your weta, it's how you use it.

You only believe that when you don't have the size.
Sinister1811
1.6 / 5 (7) Nov 19, 2011
Bear Grylls ate one of these in the New Zealand episode of Man vs Wild. Disgusting.
savvys84
not rated yet Nov 19, 2011
It's not the size of your weta, it's how you use it.

You only believe that when you don't have the size.

Lol. Thats a nice one.
Both attributes are vitally important.
YummyFur
1 / 5 (2) Nov 19, 2011
"However, Dr Wehi says there must be some cost, otherwise the size of male weta heads would just keep getting bigger and bigger."

Not really, it just means that there is a cost if they get any bigger than the limiting size they are obviously now at.
DavidMcC
not rated yet Nov 21, 2011
Dr Wehi says in the video that the cost is extra predation, but I notice that it has black and yellow stripes. Is that aposematism (ie, it looks poisonous), to reduce that cost?
rynox
1 / 5 (2) Nov 22, 2011
It's not the size of your weta, it's how you use it.

You only believe that when you don't have the size.

True, I believe it out of necessity. :)

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