Female New Zealand giraffe Weevil. Credit: Christina Painting/ Wikimedia Commons/ CC-BY-SA 4.Chandra Bahadur Dangi (a Nepalese craftman) holds the record for the world's shortest person at 54.6cm (1 ft 9 in). Sultan Ksen, a Turkish farmer who is almost five times as tall, stands at 2.52 meters (8 feet 3 inches). Nature is not known for the large differences in male size among single species. However, in a new paper, the Smithsonian Tropical Research Institute, The University of Auckland, and the University of Arizona discovered that male beetles are extremely different in size. This case provides an answer to a long-standing question in evolutionary biology: How can larger animals afford the energy cost of maintaining and making disproportionately large weapons.Nearly one in four species of beetles in the world are beetles: 350,000 species have been identified to date. Lasiorhynchus Barbicornis, a male New Zealand giraffe beetle, was known to be the longest. However, researchers discovered that the difference in weight between the largest and smallest beetles surprised them.Ummat Somjee (Earl S. Tupper fellow at STRI) said, "When I first saw their weights, I thought someone had made an error." We weighed them again, and the results were identical. The males that are the largest in size are 30% larger than their smaller counterparts. This beetle species has the largest adult size range we can find.Like many animals equipped with fighting weapons, such as elephants with trunks or antelopes with hooves, big males have snouts that seem to be disproportionately larger then the small males. As he fertilises a female, a big male dominates the situation. He uses his long snout to protect her from rivals. One of the smallest males might be sneaking underfoot to fertilize the female, even though massive males are competing for the top spot. Both large and small males can still reproduce because of both these strategies.Every ounce of energy spent in tropical forests can make the difference between life or death. Somjee is fascinated at the economics behind energy and looks to insects as an inspiration. The energetic trade-offs that the male giraffe weevils represent are literally embodied in their snouts. The snouts big males have are larger than their smaller counterparts. This makes it appear that they invest more energy and materials in their weapons than their smaller counterparts. Is this true?Chrissie Painting, a senior lecturer at University of Waikato, and a local expert on beetle weaponry, joined Somjee. They placed the males in small chambers and measured how much oxygen they consumed to determine the energy used by each. The results showed that males with larger bodies pay less energy per gram of tissue than those with smaller bodies. How is it possible for large males to carry more weapons and still have lower relative metabolic costs?The big males are very fuel efficient cars, the Prius of beetle-world (58 miles per gallon), while the smaller ones are more like Rolls Royce Phantom Coupes (14 mile per gallon). How is it possible for large males to be so efficient while still sustaining the higher energy costs associated with a larger weapon? Somjee stated.They discovered the secret to the weapon's architecture. The small snouts have a greater proportion of living tissue than our muscles, but the big snouts have a lower proportion of cuticle, like the keratin in hair and nails, which are much easier to maintain. The big males use less energy to maintain their large weapons than the smaller ones.Biology has puzzled for nearly a century over the fact that large people often have large weapons. These weevils are a reminder that large animals can reduce the cost of large structures. Ummat is now back in Panama, looking for other insect species.Somjee stated that the Giraffe weevils' unusually large size variation is what allowed us to answer the long-standing evolutionary question. "Giraffe Weevils don’t find extra energy to support their huge heads. Instead, they modify the architecture of their heads to make it more efficient and save energy.Further information: Ummat Somjee and al, Exaggeratedly selected sexual weapons with disproportionately high metabolic costs in one species with extreme size variation. Functional Ecology (2021). Information from the Journal: Functional Ecology Ummat Somjee and colleagues, Exaggerated sexually chosen weapons kept with disproportionately high metabolic costs in a single specie with extreme size variation (2021). DOI: 10.1111/1365-2435.13888
