Evolutionary responses to opposing directions of natural selection include trade-offs, where the phenotype balances selective forces, and compensation, where other traits reduce the impact of one selective force. Zooplankton pigmentation protects from ultraviolet radiation (UVR) but attracts visual predators. This trade-off is understudied in the ocean where planktonic larvae in surface waters face ubiquitous UVR and visual predation threats. We tested whether crab larvae can behaviorally reduce UVR risk through downward swimming or expansion of photoprotective chromatophores. Then we examined whether more pigmented larvae are more heavily predated by silverside fish under natural sunlight in the tropics in three UVR treatments (visible light, visible + UVA, visible + UVA + UVB). Lastly, we tested the behavioral chromatophore response of larvae to predation threats in two light treatments. Armases ricordi avoided surface waters after exposure to sunlight with UVR. Armases ricordi, Armases americanum, and Eurypanopeus sp. consistently expanded chromatophores in UVR or visible light, while Mithraculus sculptus and Mithraculus coryphe showed no response. Fish preferred pigmented larvae on sunnier days in visible light lacking UVR. Lastly, both M. coryphe and M. sculptus unexpectedly expanded chromatophores in fish cues, but responses were inconsistent over trials and across light treatments. The more consistent larval responses to UVR than to predator cues and the lack of predator preferences in natural light conditions suggest that UVR may have a stronger influence on pigmentation than predation. This study improves our understanding of planktonic adaptation to countervailing selection caused by visual predation and exposure to UVR.

中文翻译：

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在对抗紫外线和捕食的威胁下浮游动物色素沉着的成本和补偿。

对自然选择的相反方向的进化反应包括权衡（表型平衡选择力）和补偿（其他特征减少一种选择力的影响）。浮游动物色素沉着可防止紫外线（UVR），但会吸引视觉掠食者。在海洋中对这种折衷的研究不足，在海洋中，地表水中的浮游幼虫面临着无处不在的UVR和视觉掠食威胁。我们测试了蟹幼虫是否可以通过向下游泳或扩大光保护性色谱而行为上降低UVR风险。然后，我们通过三种UVR处理（可见光，可见光+ UVA，可见光+ UVA + UVB）在热带地区的自然阳光下检查了银侧鱼是否更多地吸收了有色幼虫。最后，我们在两种光照处理下测试了幼虫对捕食威胁的行为色谱反应。Armases ricordi在暴露于具有UVR的阳光下避免了地表水。Armases ricordi，Armases americanum和Eurypanopeus sp.。在UVR或可见光下，色谱柱始终保持扩展状态，而密鳞鱼和紫薇却没有反应。鱼在缺乏紫外线辐射的可见光下，在阳光充沛的日子里更喜欢有色幼虫。最后，M。coryphe和M. sculptus都意外地扩大了鱼线索中的色谱，但是在试验和光照处理中反应不一致。幼虫对UVR的反应要比对捕食者的线索更为一致，并且在自然光条件下缺乏对捕食者的偏好，这表明UVR对色素沉着的影响可能比对捕食的影响更大。