Meeting Abstract
Horns in antelopes, tusks in elephants and antlers in deer are all examples of animal weapons. The largest and most exaggerated of these structures are often used in competition among males for mating opportunities with females. These large structures are predicted to be energetically expensive for animals to maintain and carry. Yet, the costs associated with the metabolic maintenance of these traits for individuals of different sizes remains a major gap in our understanding of positive size scaling. We examine an insect with enlarged hind legs used as weapons in male-male combat. We capitalize on the behavior of this insect, which autotomizes its sexually selected weapon (without regeneration), to isolate the metabolic rate associated with maintenance of these traits. Using flow-through respirometry we measure the aerobic cost of the weapon by measuring CO2 production rates before and after leg-autotomy. We find that larger males had proportionally larger weapons for their body size, and that larger males also had proportionally higher metabolic rates compared to females or to small males. A sexually selected weapon accounted for a large proportion (23%) of energy expenditure at rest, and metabolic enzyme assays reveal highly metabolically active tissue, suggestive of high metabolic maintenance costs of these weapons. These energetic maintenance costs remain a largely unexplored avenue to understand the forces that shape the positive size allometries of sexually selected weapons so ubiquitous in nature.
