The parallel evolution of similar ecotypes in response to comparable environmental conditions is believed to reveal the importance of divergent selection in phenotypic diversifying processes. Systems characterized by the presence of multiple replicate populations expressing resource polymorphism thus provide an ideal opportunity to address the occurrence and factors affecting the parallel evolution of ecotypes. Previous studies have shown that brook charr (Salvelinus fontinalis) exhibit resource polymorphism in some Canadian Shield lakes, where a littoral ecotype feeds mainly on zoobenthos and a pelagic ecotype feeds mostly on zooplankton. Using morphological traits and geometric morphometric analyses on 18 native brook charr populations, we explicitly tested (i) whether brook charr ecotypes show parallel evolution across populations (i.e. the same morphological traits discriminate ecotypes among lakes) and (ii) whether interspecific competition decreases the amplitude of morphological differentiation between ecotypes, if any, because brook charr experience some level of competitive exclusion from the littoral habitat in the presence of creek chub or white sucker. We observed a low level of parallel evolution, where the littoral ecotype was overall stouter with longer fins and smaller eyes than the pelagic ecotype. Interspecific competition had no clear impacts on the amplitude of morphological differentiation. We also observed that inter-lake morphological differences are greater than between ecotypes within lakes, suggesting an important effect of local environmental factors on population morphology. Early-stage of diversification as well as phenotypic plasticity and morphological integration could explain why resource polymorphism is still subtle in brook charr populations.

类似生态型响应可比环境条件的平行进化被认为揭示了不同选择在表型多样化过程中的重要性。因此，以存在表达资源多态性的多个重复种群为特征的系统为解决影响生态型平行进化的发生和因素提供了理想的机会。以前的研究表明，小溪鱼 ( Salvelinus fontinalis) 在一些加拿大地盾湖中表现出资源多态性，其中沿海生态型主要以底栖动物为食，而远洋生态型主要以浮游动物为食。使用对 18 个本地小溪夏尔种群的形态特征和几何形态计量分析，我们明确测试了 (i) 小溪夏尔生态型是否显示出跨种群的平行进化（即相同的形态特征区分湖泊之间的生态型）以及（ii）种间竞争是否降低了振幅生态型之间的形态差异，如果有的话，因为在小溪鲢或白色吸盘存在的情况下，小溪夏尔从沿海栖息地经历了一定程度的竞争性排斥。我们观察到低水平的平行进化，与远洋生态型相比，沿海生态型总体上更粗壮，鳍更长，眼睛更小。种间竞争对形态分化的幅度没有明显影响。我们还观察到湖间形态差异大于湖泊内生态型之间的差异，表明当地环境因素对种群形态有重要影响。多样化的早期阶段以及表型可塑性和形态整合可以解释为什么在布鲁克夏尔种群中资源多态性仍然很微妙。