The hidden cost of sexually selected traits: the metabolic expense of maintaining a sexually selected weapon
The hidden cost of sexually selected traits: the metabolic expense of maintaining a sexually selected weapon
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DOI：
10.1098/rspb.2018.1685
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发表时间：
2018-11
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影响因子：
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通讯作者：
Ummat Somjee;Ummat Somjee;H. Woods;M. Duell;Christine W. Miller
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作者：
Ummat Somjee;Ummat Somjee;H. Woods;M. Duell;Christine W. Miller
性别选择武器是自然界中最夸张的特征之一。性选择理论经常假设这种夸张的代价很高；然而，这些成本很少被衡量。我们对维持这些特征所需要的能量资源知之甚少，也不知道体型最大的个体与体型最小的个体在能量消耗上的差异。这方面的知识至关重要；静息代谢率可占野生动物每日能量消耗的30-40%。在这里，我们利用自切现象来对武器维护成本进行独特的观察。我们利用三色细绒纤毛虫（半翅目：细绒纤毛虫科）测量了武器脱落前后的CO2产率。这种昆虫的雄性在雄性之间的战斗中使用扩大的后股骨作为武器，但在被困时，它们可以很容易地脱落，而不会再生。我们发现，失去腿后，男性的代谢率平均下降了23.5%，女性的代谢率平均下降了7.9%。值得注意的是，体型较大的雄性每失去一克武器的代谢率下降幅度较小。我们的研究结果表明，性别选择的武器对雄性的静息代谢率有很大贡献，但这些代价并不与体型成正比；体型较大的雄性可以拥有更大的武器，以减少代谢成本。这些精力充沛的维护成本可能是性选择武器异速进化的组成部分，但它们在很大程度上仍未被探索。
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.