Division of Aquatic Ecology & Evolution, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland.
J Evol Biol. 2013 Jul;26(7):1578-87. doi: 10.1111/jeb.12166. Epub 2013 May 25.
North temperate fish in post-glacial lakes are textbook examples for rapid parallel adaptive radiation into multiple trophic specialists within individual lakes. Speciation repeatedly proceeded along the benthic-limnetic habitat axis, and benthic-limnetic sister species diverge in the number of gill rakers. Yet, the utility of different numbers of gill rakers for consuming benthic vs. limnetic food has only very rarely been experimentally demonstrated. We bred and raised families of a benthic-limnetic species pair of whitefish under common garden conditions to test whether these species (i) show heritable differentiation in feeding efficiency on zooplankton, and (ii) whether variation in feeding efficiency is predicted by variation in gill raker numbers. We used zooplankton of three different size classes to investigate prey size dependency of divergence in feeding efficiency and to investigate the effect strength of variation in the number of gill rakers. Our results show strong interspecific differences in feeding efficiency. These differences are largest when fish were tested with the smallest zooplankton. Importantly, feeding efficiency is significantly positively correlated with the number of gill rakers when using small zooplankton, also when species identity is statistically controlled for. Our results support the hypothesis that a larger number of gill rakers are of adaptive significance for feeding on zooplankton and provide one of the first experimental demonstrations of trait utility of gill raker number when fish feed on zooplankton. These results are consistent with the suggested importance of divergent selection driven feeding adaptation during adaptive radiation of fish in post-glacial lakes.
北温带湖泊中的鱼类是快速平行适应辐射到单个湖泊中多个营养特化种的典型例子。物种形成沿着底栖-上层生境轴反复进行，底栖-上层姐妹种在鳃耙数上存在分歧。然而，不同数量的鳃耙用于消耗底栖和上层食物的效用仅在极少数情况下得到了实验证明。我们在共同花园条件下培育和饲养了一对白鱼的底栖-上层物种的家族，以测试这些物种：（i）在摄食浮游动物的效率上是否存在可遗传的差异；（ii）摄食效率的变化是否可以通过鳃耙数的变化来预测。我们使用了三种不同大小类别的浮游动物来研究摄食效率差异的猎物大小依赖性，并研究了鳃耙数变化的效应强度。我们的结果表明，摄食效率存在强烈的种间差异。当用最小的浮游动物测试鱼类时，这些差异最大。重要的是，当使用小浮游动物并且在统计学上控制了物种身份时，摄食效率与鳃耙数呈显著正相关。我们的结果支持这样的假设，即更多的鳃耙对于摄食浮游动物具有适应性意义，并提供了鱼类在摄食浮游动物时鳃耙数的特征有用性的第一个实验证明之一。这些结果与在冰川后湖泊中鱼类的适应性辐射过程中，趋异选择驱动的摄食适应的重要性相一致。
