June 25, 2022

The largest tournament competitions in the world take place on certain rotting trees in the New Zealand bush, where hordes of males battle for opportunities to mate. The knights are not humans, but New Zealand giraffe weevils, a species of beetle with a snout like a lance. The largest males hit each other with the snout until the other either withdraws or is unceremoniously pushed from the bark.

The competition is particularly fierce because there is an impressive range of sizes for male giraffe weevils: the largest male weevil is 30 times larger than the smallest. In human terms, this would be like having a friend the size of two adult giraffes combined.

As male weevils get larger, their snouts become disproportionately long, suggesting that the largest males use relatively more energy to guide their huge heads. Some biologists have theorized that these exaggerated traits are honest indicators of how well the animal is suited as a potential partner or competitor; According to this logic, a weak moose would not have the energy necessary to obtain huge horns.

However, an article published Friday in the journal Functional Ecology reports that New Zealand’s largest giraffe weevils actually use relatively less energy than their smaller relatives thanks to an energy-saving anatomical hack.

Ummat Somjee, evolutionary biologist at the Smithsonian Tropical Research Institute in Panama and author of the article, originally studied leaf-pod beetles to understand how much energy the beetles use for their massive hind legs.

One day, Dr. Somjee in a Panamanian jungle on a decaying tree trunk that was teeming with knighting weevils. “It was like a little war zone on the record,” said Dr. Somjee. (The Panamanian species is depicted in the tweets embedded below.)

Dr. Somjee learned that these weevils had an even stranger cousin, the New Zealand giraffe weevil. The huge difference in size between male adult New Zealand giraffe weevils made the species an ideal candidate for studying the energy costs of a range of snout sizes.

He reached out to Chrissie Painting, a behavioral ecologist at the University of Waikato in New Zealand and author of the study that began studying weevils in 2009. In 2019, Dr. Painting Dr. Somjee to her secret gathering place, which she calls “weevil town”.

If scared, a New Zealand giraffe weevil will pounce from a tree. In order to collect masses of weevils, Dr. Painting an ice bucket under the tree, waving his hand and watching the weevils tipped into the bucket at the same time.

Back in Dr. In Paintings Laboratory, the researchers measured the metabolic rates of their potpourri of weevils. They placed the weevils in sealed glass syringes – their long bodies seemed made for the tubes – and measured their dormancy when they were resting. They also placed the weevils on tiny treadmills to measure the amount of energy expended on a quick trot. Both results showed that larger weevils used less energy per gram of tissue than smaller weevils. In other words, 30 small weevils would use significantly more energy than the largest weevils, which are the size of 30 small weevils.

These results may seem confusing – wouldn’t a stick-headed weevil use a lot more energy? The researchers decapitated their weevils, dried the heads in an oven, and placed them in a solution to digest living tissue but preserve the cuticle, an inert hard tissue.

They found that larger weevils have weevils and legs that always contain more cuticles and less metabolically active tissue than smaller weevils. “It’s a really cheap way to get bigger,” said Dr. Somjee. In fact, the largest males, the smallest males and females devoted roughly the same percentage of their snout to soft, energy-guzzling tissue.

The researchers compared their own metabolic data with a number of other insect species, as there was no other insect of this size. The pattern they found in their own data that larger weevils used relatively less energy per gram of tissue was consistent across species.

Douglas Emlen, a biologist at the University of Montana who was not involved in the research, says the new paper confirms the long-standing theory that exaggerated weapons are honest properties; for example, a bigger snout means a stronger weevil.

But the new research also shows guns are disproportionately expensive for short men, said Dr. Emlen.

“We all focus on the really big males,” he said. “But what matters is whether the little ones can fake it.” They can’t, he adds, and that makes a big snout an honest sign of a stocky weevil body.

Adult weevils do not grow. “When you show up as a little man, there is no going back,” said Dr. Painting. That’s why the smallest weevils have devised an alternative mating strategy to balance their stocky sniffers: they sneak under larger males to mate with females. But they are still not as successful as their bigger rivals and are also dying younger, said Dr. Painting.

Even medium-sized weevils have a hard time being too small to compete and too big to sneak.

“There’s nothing fair about nature,” said Dr. Emlen. “The rich get richer and the poor get poorer.”

Unfortunately, the bugs that got the short end of the snout really seem to be the smaller of two weevils.