Plasticity in Daphnia eye size is determined by intra-generational environmental conditions

Variation in structure and size of the eye in relation to light environments is well-documented across animal taxa. However, the long-term effects of ultraviolet radiation (UVR) on eye size across generations remain understudied, despite natural fluctuations in UVR being common in aquatic habitats. Here, we used Daphnia magna to test whether an evolutionary history of UVR threat modifies plasticity and transgenerational responses in eye size. We conducted a reciprocal split-brood experiment across three parthenogenetic generations using two groups maintained under either UVR or non-UVR conditions for over 150 generations, enabling the potential accumulation of adaptive responses and the establishment of distinct evolutionary lineages for comparison. We found strong plasticity in eye size, primarily shaped by current environmental conditions rather than transgenerational effects. Smaller eyes developed in response to UVR but rapidly reverted to larger dimensions in its absence. Furthermore, changes in relative eye size were associated with fitness-related traits, including swimming behaviour and reproductive output, although these relationships varied in strength and direction between UVR-exposed and unexposed individuals. Our study highlights the role of environmental stressors and evolutionary history in shaping sensory adaptations, providing conceptual advances on how sensory traits among aquatic invertebrates may rapidly evolve under changing environmental conditions.

动物各分类群中，眼部结构与大小随光照环境产生的变异已有大量研究佐证。然而，尽管紫外线辐射（Ultraviolet Radiation, UVR）的自然波动在水生环境中十分常见，但跨世代紫外线辐射对眼部大小的长期影响仍未得到充分研究。本研究以大型溞（Daphnia magna）为实验对象，探究紫外线辐射的演化历史是否会改变眼部大小的可塑性及跨世代响应。我们开展了跨三个孤雌生殖世代的互交分巢实验，采用两个分别在紫外线辐射与非紫外线辐射环境中维持超过150代的种群，从而为适应性响应的潜在积累以及可用于对比的不同演化谱系的建立提供了条件。研究结果显示，眼部大小存在显著的可塑性，且这种可塑性主要受当前环境条件调控，而非跨世代效应影响：在紫外线辐射环境下，个体眼部发育得更小，而当移除紫外线辐射后，眼部大小会快速恢复至更大的尺寸。此外，相对眼部大小的变化与游泳行为、繁殖产出等适合度相关性状存在关联，不过这种关联的强度与方向在暴露于紫外线辐射与未暴露的个体间存在差异。本研究强调了环境胁迫与演化历史在感官适应性塑造中的作用，为理解水生无脊椎动物的感官性状如何在环境变化下快速演化提供了理论进展。