Drop your weapons! Autotomy, the shedding of a body part, reveals the hidden cost of conflict

November 15, 2018, Smithsonian Tropical Research Institute

Animal weapons such as antlers, tusks and limbs specialized for fighting require a large energy expenditure to produce and may cost even more to maintain. Because the leaf-footed bug sheds its large hind limbs, used as weapons in male-male battles, scientists working at the Smithsonian Tropical Research Institute (STRI) in Panama could measure energy use of live bugs with and without hind legs to calculate the hidden energetic cost of weapons' maintenance.

Wild animals can spend up to 30 and 40 percent of their total energy budget while at rest. "Human athletes often burn more calories during their relatively long rest periods than during physical exercise itself," said Ummat Somjee, who did this study as part of his doctoral dissertation at the University of Florida in co-author Christine Miller's lab group and is currently a Tupper post-doctoral fellow at STRI.

"We calculated the metabolic cost of maintaining large hind legs in a leaf-footed bug and found that males invest more in weapons than females do," Somjee said. "Large males expend relatively less energy on their super-sized weapons than smaller males." The results are published online in Proceedings of the Royal Society B.

Male leaf-footed bugs, Leptoscelis tricolor, hang out on bright orange or red heliconia inflorescences, feeding on nectar and developing heliconia fruit. Their hind legs, covered with thorny structures, are larger than females' legs and serve as weapons in male-male duels.

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