Abstract：
Hybridization between divergent lineages can result in losses of distinct evolutionary taxa. Alternatively, hybridization can lead to increased genetic variability that may fuel local adaptation and the generation of novel traits and/or taxa. Here, we examined single-nucleotide polymorphisms generated using genotyping-by-sequencing in a population of Dolly Varden char (Pisces: Salmonidae) that is highly admixed within a contact zone between two subspecies (Salvelinus malma malma, Northern Dolly Varden [NDV] and S. m. lordi, Southern Dolly Varden [SDV]) in southwestern Alaska to assess the spatial distribution of hybrids and to test hypotheses on the origin of the admixed population. Ancestry analysis revealed that this admixed population is composed of advanced generation hybrids between NDV and SDV or advanced backcrosses to SDV; no F1 hybrids were detected. Coalescent-based demographic modelling supported the origin of this population about 55,000 years ago by secondary contact between NDV and SDV with low levels of contemporary gene flow. Ancestry in NDV and SDV varies within the watershed and ancestry in NDV was positively associated with distance upstream from the sea, contingent on habitat-type sampled, and negatively associated with the number of migrations that individual fish made to the sea. Our results suggest that divergence between subspecies over hundreds of thousands of years may not be associated with significant reproductive isolation, but that elevated diversity owing to hybridization may have contributed to adaptive divergence in habitat use and life history.
摘要：
不同谱系之间的杂交会导致不同进化分类单元的丢失。或者，杂交可导致增加的遗传变异性,其可促进局部适应和新性状和/或分类群的产生。这里,我们检查了使用基因分型通过测序在多莉·瓦登char（双鱼座：沙门氏菌科）种群中产生的单核苷酸多态性，该种群在两个亚种（Salvelinusmalmamalma，北多莉·瓦尔登[NDV]和S.m.洛迪，阿拉斯加西南部的SouthernDollyVarden[SDV]），以评估杂种的空间分布并检验混合种群起源的假设。祖先分析显示，该混合种群由NDV和SDV之间的高级世代杂种或与SDV的高级回交组成；未检测到F1杂种。基于合并的人口统计学模型在大约55,000年前通过NDV和SDV之间的二次接触以及低水平的当代基因流来支持该人群的起源。NDV和SDV的祖先在分水岭内变化，NDV的祖先与海洋上游的距离呈正相关，视采样的栖息地类型而定，并与单个鱼类向海洋迁移的数量呈负相关。我们的结果表明，数十万年来亚种之间的差异可能与明显的生殖隔离无关。但是由于杂交而增加的多样性可能导致了栖息地使用和生活史的适应性差异。
