Large and exaggerated sexually selected weapons comprise high proportions of metabolically inexpensive exoskeleton

The cost-minimization hypothesis proposes that positive allometry in
sexually selected traits can be explained if the proportional energetic
maintenance costs of weapons decrease as traits increase in size.
Energetic maintenance costs are the costs of maintaining homeostasis. They
are slow, persistent energy sinks that are distinct from ephemeral costs
of growth. Because some tissues expend more energy on maintenance than
others, energetic maintenance costs can be inferred from proportional
tissue composition. For example, soft tissues require more energy for
maintenance than exoskeleton, so an arthropod claw that is 50% soft tissue
and 50% exoskeleton would have higher energetic maintenance costs than one
that is 30% soft tissue and 70% exoskeleton. I tested the
cost-minimization hypothesis using proportional tissue composition as a
proxy for energetic maintenance costs in snapping shrimp ( Alpheus
heterochaelis and Alpheus estuariensis ) and fiddler crabs ( Uca pugilator
). As predicted, larger weapons comprised proportionally less soft tissue
mass and more exoskeleton mass than smaller weapons. Furthermore, I
extended cost-minimization to explain trait exaggeration: individuals
might exaggerate traits by investing more mass in exoskeleton. As
predicted, exoskeleton mass proportional to weapon mass increased as
exaggeration increased. These results support and extend the
cost-minimization hypothesis to explain positive allometry and weapon
exaggeration.

成本最小化假说（cost-minimization hypothesis）提出，性选择性状的正异速生长（positive allometry）可通过以下机制得到解释：当性状尺寸增大时，武器类性选择性状的比例性能量维持成本会随之降低。
能量维持成本指维持生物体内稳态（homeostasis）所需的能耗，属于缓慢且持续的能量消耗源，与生长过程中的瞬时能耗存在本质差异。由于不同组织的维持能耗水平存在显著区别，能量维持成本可通过组织的比例组成进行推断。例如，软组织（soft tissue）的维持能耗高于外骨骼（exoskeleton），因此软组织占比50%、外骨骼占比50%的节肢动物螯（arthropod claw），其能量维持成本要高于软组织占比30%、外骨骼占比70%的螯。
本研究以组织比例组成作为能量维持成本的替代指标（proxy），针对鼓虾（snapping shrimp，Alpheus heterochaelis、Alpheus estuariensis）与招潮蟹（fiddler crabs，Uca pugilator）开展了成本最小化假说的验证实验。实验结果与预期一致：相较于小型螯，大型螯的软组织质量占比更低，外骨骼质量占比更高。
此外，本研究将成本最小化假说拓展至性状夸张现象的解释范畴：个体可通过向外骨骼投入更多质量来实现性状夸张。实验结果同样符合预期：随着性状夸张程度提升，外骨骼质量占武器总质量的比例随之升高。
上述研究结果支持并拓展了成本最小化假说，为解释正异速生长与武器类性状夸张提供了坚实的理论支撑。