Data from: How parallel is parallel evolution? A comparative analysis in fishes

Evidence of phenotypic parallelism is often used to infer the deterministic role played by natural selection. However, variation in the extent or direction of divergence is often evident among independent evolutionary replicates, raising the following question: just how parallel, overall, is parallel evolution? We answer this question through a comparative analysis of studies of fishes, a taxon where parallel evolution has been much discussed. We first ask how much of the among-population variance in phenotypic traits can be explained by different “environment” types, such as high predation versus low predation or benthic versus limnetic. We then use phenotypic change vector analysis to quantify variation in the direction (vector angles) and magnitude (vector lengths) of environment-associated divergence. All analyses show high variation in the extent of parallelism—from very high to very low, along with everything in between—highlighting the importance of quantifying parallelism rather than just asserting its presence. Interestingly, instances of low extents of parallelism represent important components of divergence in many cases, promising considerable opportunities for inferences about the factors shaping phenotypic divergence.

表型平行性（phenotypic parallelism）的相关证据常被用于推断自然选择所扮演的决定性角色。然而，不同独立进化重复类群间的分化程度或分化方向往往存在差异，由此引出如下问题：总体而言，平行进化（parallel evolution）究竟能达到何种程度？本研究通过对鱼类类群相关研究的比较分析解答了这一问题——鱼类是平行进化被广泛探讨的类群之一。我们首先探讨：表型性状的种群间方差，在多大程度上可由不同的"环境"类型（如高捕食压力环境与低捕食压力环境、底栖生境与湖沼生境）所解释？随后，我们采用表型变化向量分析，对与环境相关的分化的方向（向量夹角）和强度（向量长度）的变异进行量化。所有分析结果均表明，平行进化的程度存在极高变异——从极高水平到极低水平，覆盖所有中间状态——这凸显了量化平行性而非仅断言其存在的重要性。值得注意的是，在诸多案例中，低平行性程度的实例本身便是进化分化的重要组成部分，这为探究塑造表型分化的各类因素提供了可观的研究契机。