Mouth asymmetry in the textbook example of scale-eating cichlid fish is not a discrete dimorphism after all
Mouth asymmetry in the textbook example of scale-eating cichlid fish is not a discrete dimorphism after all
复制标题
DOI：
10.1098/rspb.2012.2082
复制
发表时间：
2012-12-07
影响因子：
4.7
通讯作者：
Meyer, Axel
中科院分区：
文献类型：
--
作者：
Kusche, Henrik;Lee, Hyuk Je;Meyer, Axel
来自坦噶尼喀湖的食鳞慈鲷，Perissodus microlepis，往往有明显不对称的头部，要么向左弯曲，要么向右弯曲。“左”变体明显地向左张开嘴，优先从受害者鱼的右手边的鳞片上进食，而“右”变体从受害者的左手边咬鳞片。这种惊人的二型性使这些鱼成为其惊人的生态专业化程度的教科书范例，也是少数已知的负频率依赖选择作用于不对称形态特征的事件之一，其中左和右形式在一个物种中同样频繁。我们调查了细鳞松头部不对称的频率分布的程度和形状，以测试这种变化是否符合通常假设的离散二型性。在成鱼和幼鱼，嘴不对称似乎是连续和单峰分布，没有明确的证据为离散二型。混合物分析没有发现证据的离散，甚至强烈的二型性。这些结果引起了对以前的说法的怀疑，如教科书中所报道的，即小鳞松的头部变异代表了左弯曲和右弯曲形式的离散二型性。基于广泛的实地采样，排除模棱两可的（即对称或弱不对称）个别成年人，我们发现，左和右变形发生在相同的丰度在五个人口。此外，交配配对51野生捕获对随机头部偏侧性，质疑报告说，这种偏侧性是通过dispersionative交配。
Individuals of the scale-eating cichlid fish, Perissodus microlepis, from Lake Tanganyika tend to have remarkably asymmetric heads that are either left-bending or right-bending. The 'left' morph opens its mouth markedly towards the left and preferentially feeds on the scales from the right-hand side of its victim fish, and the 'right' morph bites scales from the victims' left-hand side. This striking dimorphism made these fish a textbook example of their astonishing degree of ecological specialization and as one of the few known incidences of negative frequency-dependent selection acting on an asymmetric morphological trait, where left and right forms are equally frequent within a species. We investigated the degree and the shape of the frequency distribution of head asymmetry in P. microlepis to test whether the variation conforms to a discrete dimorphism, as generally assumed. In both adult and juvenile fish, mouth asymmetry appeared to be continuously and unimodally distributed with no clear evidence for a discrete dimorphism. Mixture analyses did not reveal evidence of a discrete or even strong dimorphism. These results raise doubts about previous claims, as reported in textbooks, that head variation in P. microlepis represents a discrete dimorphism of left- and right-bending forms. Based on extensive field sampling that excluded ambiguous (i.e. symmetric or weakly asymmetric) individual adults, we found that left and right morphs occur in equal abundance in five populations. Moreover, mate pairing for 51 wild-caught pairs was random with regard to head laterality, calling into question reports that this laterality is maintained through disassortative mating.