Data from: Selection on incremental variation of eye size in a wild population of Daphnia

Several studies of eye morphology have analyzed macroevolutionary patterns in the diversity of eyes, and though these studies are often linked to environment or behavior, they provide only indirect evidence of selection. Specific data to show the microevolutionary potential for adaptation by natural selection in eye morphology has been lacking. We document directional selection on eye size, an important determinant of visual capabilities, in a wild population of the freshwater microcrustacean Daphnia. We show that even slight changes in eye size may have major consequences for fitness. An increase of eye diameter of 19.9 μm – slightly more than one standard deviation – is associated with an increase in clutch size of one egg, or an increase of nearly 20% of the mean clutch size. Furthermore, relative eye size is genetically variable, and thus could evolve in response to the observed selective pressure. We conclude that selection on incremental variation in eye size may have led to differences observed on broader taxonomic scales.已有多项针对眼部形态的研究，分析了眼部多样性的宏观进化（macroevolutionary）模式；尽管此类研究常与环境或行为相关联，但仅能为选择作用提供间接证据。此前始终缺乏能够直接证明眼部形态可通过自然选择发生适应性微进化（microevolutionary）的具体数据。本研究针对淡水微型甲壳动物水蚤（Daphnia）的野生种群，记录了眼部大小——视觉功能的重要决定因素——所受到的定向选择（directional selection）作用。研究发现，即便眼部大小发生微小变化，也可能对适合度产生显著影响：眼径每增加19.9μm（略大于1个标准差），便可使每窝产卵量增加1枚，相较平均每窝产卵量提升近20%。此外，相对眼大小存在遗传变异，因此可响应观测到的选择压力发生进化。综上，本研究认为，针对眼大小增量变异的选择作用，或许正是更宽泛分类阶元尺度上眼部形态差异的成因之一。