The hidden cost of sexually selected traits: The metabolic expense of maintaining a sexually selected weapon

Ummat Somjee, H. Arthur Woods, Meghan Duell, Christine W. Miller

Research output: Contribution to journalArticlepeer-review

48 Scopus citations


Sexually selected weapons are among the most exaggerated traits in nature. Sexual selection theory frequently assumes a high cost of this exaggeration; yet, those costs are rarely measured. We know very little about the energetic resources required to maintain these traits at rest and the difference in energetic costs for the largest individuals relative to the smallest individuals. Knowledge in this area is crucial; resting metabolic rate can account for 30 – 40% of daily energy expenditure in wild animals. Here, we capitalized on the phenomenon of autotomy to take a unique look at weapon maintenance costs. Using Leptoscelis tricolor (Hemiptera: Coreidae), we measured CO2 production rates before and after a weapon was shed. Males in this insect species use enlarged hind femora as weapons in male – male combat, and yet can shed them readily, without regeneration, upon entrapment. We found that metabolic rate decreased by an average of 23.5% in males after leg loss and by 7.9% in females. Notably, larger males had less of a drop in metabolic rate per gram of weapon lost. Our findings suggest that sexually selected weapons contribute to a large portion of resting metabolic rate in males, but these costs do not scale in direct proportion to size; larger males can have larger weapons for a reduced metabolic cost. These energetic maintenance costs may be integral to the evolution of the allometries of sexually selected weapons, and yet they remain largely unexplored.

Original languageEnglish
Article number20181685
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1891
StatePublished - Nov 21 2018


  • Energy budgets
  • Honest signalling
  • Hypermetric allometry
  • Resting metabolic rate
  • Sexually selected weapons
  • Tissue-specific metabolic rate


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