Eye loss has been a long‐standing interest in evolutionary biology. Many organisms that inhabit environments without light penetration, for example the deep sea, exhibit eye loss and thus become blind. However, water‐depth distribution of eyes in marine organisms is poorly understood. Ostracods are widely distributed crustaceans, and many sighted marine ostracods have eye tubercles (lenses) on their shells. Since eye tubercles are visible on the shells illustrated in much literature, it is easy to determine their presence or absence via a literature survey. Here, we used a large Arctic‐wide ostracod census dataset (Arctic Ostracode Database) to calculate the eye index (the percentage of species with eyes), and compare them with water depth and light availability. As water depth increases, eye index values decrease and become constantly zero in water deeper than 1000 m. Similar decline of sighted species with increasing depth is also known in isopods and amphipods, suggesting that it may be common in other crustaceans and perhaps in deep‐sea organisms in general. We also show that eye index values increase as light availability increases. This study is the first to quantify how distributions of sighted and blind species change with light availability, giving baseline information on vision in the deep sea.

中文翻译：

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视力与失明：北冰洋介形类眼睛、水深和光照情况之间的关系


眼睛丧失一直是进化生物学的一个长期关注点。许多生活在没有光穿透的环境中的生物体，例如深海，会出现视力丧失，从而失明。然而，人们对海洋生物眼睛的水深分布知之甚少。介形类是分布广泛的甲壳类动物，许多有视力的海洋介形类的壳上都有眼结节（晶状体）。由于许多文献中所描绘的贝壳上都可见眼结节，因此通过文献调查很容易确定它们是否存在。在这里，我们使用大型北极介形类普查数据集（北极介形类数据库）来计算眼睛指数（有眼睛的物种的百分比），并将其与水深和光照可用性进行比较。随着水深的增加，眼指数值减小，并且在深度超过 1000 m 的水中始终为零。随着深度的增加，有视力的物种也出现类似的衰退现象，这在等足类动物和片脚类动物中也存在，这表明这种现象可能在其他甲壳类动物中很常见，甚至可能在整个深海生物中也很常见。我们还表明，眼睛指数值随着光照可用性的增加而增加。这项研究首次量化了有视力和失明物种的分布如何随光照变化而变化，提供了深海视力的基线信息。