Data from: Striking phenotypic variation yet low genetic differentiation in sympatric lake trout (Salvelinus namaycush)

The study of population differentiation in the context of ecological speciation is commonly assessed using populations with obvious discreteness. Fewer studies have examined diversifying populations with occasional adaptive variation and minor reproductive isolation, so factors impeding or facilitating the progress of early stage differentiation are less understood. We detected non-random genetic structuring in lake trout (Salvelinus namaycush) inhabiting a large, pristine, postglacial lake (Mistassini Lake, Canada), with up to five discernible genetic clusters having distinctions in body shape, size, colouration and head shape. However, genetic differentiation was low (FST = 0.017) and genetic clustering was largely incongruent between several population- and individual-based clustering approaches. Genotype- and phenotype-environment associations with spatial habitat, depth and fish community structure (competitors and prey) were either inconsistent or weak. Striking morphological variation was often more continuous within than among defined genetic clusters. Low genetic differentiation was a consequence of relatively high contemporary gene flow despite large effective population sizes, not migration-drift disequilibrium. Our results suggest a highly plastic propensity for occupying multiple habitat niches in lake trout and a low cost of morphological plasticity, which may constrain the speed and extent of adaptive divergence. We discuss how factors relating to niche conservatism in this species may also influence how plasticity affects adaptive divergence, even where ample ecological opportunity apparently exists.

在生态物种形成（ecological speciation）的研究框架下，种群分化的常规评估对象通常是具有明显离散特征的种群。针对具有偶发性适应性变异和较弱生殖隔离的分化中的种群的研究相对较少，因此阻碍或促进早期分化进程的相关机制仍未得到充分阐释。我们在栖息于加拿大一处大型原始冰后湖（postglacial lake）——米斯塔西尼湖（Mistassini Lake）的湖鳟（Salvelinus namaycush）种群中检测到了非随机遗传结构，该种群可被划分为最多5个可识别的遗传簇，各簇在体型、大小、体色及头部形态上均存在差异。然而，其遗传分化程度较低（FST = 0.017），且基于种群和基于个体的多种聚类方法所得到的遗传聚类结果在很大程度上并不一致。基因型、表型与空间生境、水深及鱼类群落结构（竞争者与猎物）之间的关联要么缺乏一致性，要么强度较低。显著的形态变异在划定的遗传簇内部往往比簇间更为连续。尽管种群有效规模较大，但较低的遗传分化实则是当代基因流水平较高的结果，而非迁移-漂变不平衡（migration-drift disequilibrium）所致。本研究结果表明，湖鳟具有极强的占据多种生境生态位的表型可塑性倾向，且形态可塑性的成本较低，这可能会限制适应性分化的速度与程度。我们还讨论了该物种的生态位保守性（niche conservatism）相关因子，即便在存在充足生态机遇的情况下，这些因子也可能会影响表型可塑性对适应性分化的作用效果。