Evolutionary theory suggests that individuals should express costly traits at a magnitude that optimizes the cost-benefit difference for the trait-bearer. Trait expression varies across a species because costs and benefits vary among individuals. For example, if large individuals pay lower costs than small individuals, then larger individuals should reach optimal cost-benefit differences at a greater magnitude of trait expression. Using the remarkable cavitation-shooting weapons found in the big claws of male and female alpheid snapping shrimp, we test whether size- and sex-dependent expenditures explain the scaling of weapon size relative to body size and why males have larger proportional weapon size than females. We found that males and females from three snapping shrimp species (Alpheus heterochaelis, Alpheus angulosus, and Alpheus estuariensis) show patterns consistent with resource allocation tradeoffs between weapon and abdomen size. For male A. heterochaelis, the species for which we had the greatest sample size and statistical power, the smallest individuals showed the steepest tradeoff. Our extensive dataset in A. heterochaelis also included data about pairing, breeding season, and egg clutch size. Therefore, we could test for reproductive tradeoffs and benefits in this species. Female A. heterochaelis exhibited additional tradeoffs between weapon size and egg count, average egg volume, and total egg mass volume. For average egg volume, the smallest females exhibited the steepest tradeoff relative to weapon size. Furthermore, in males but not females, large weapons were positively correlated with the probability of being paired and the relative size of their pair mate. In conclusion, we establish that size-dependent tradeoffs underlie reliable scaling relationships of costly traits. Furthermore, we show that males and females differ in weapon investment, suggesting that weapons are especially beneficial to males and especially burdensome to females.
Data, metadata, and code are available on Dryad: https://doi.org/10.5061/dryad.qz612jmkf
Tradeoffs and benefits explain scaling, sex differences, and seasonal oscillations in the remarkable weapons of snapping shrimp (Alpheus spp.)Dryad Digital Repository, doi:10.5061/dryad.qz612jmkf.
Weapon performance and contest assessment strategies of the cavitating snaps in snapping shrimpDryad Digital Repository, doi:10.5061/dryad.qz612jmjx.
- S N Patek
- Jason P Dinh
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Lauren A O'Connell, Stanford University, United States
© 2023, Dinh & Patek
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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