Two genetically separate brown trout populations are studied following their release into an environment previously void of this species. We use a pooled sequencing approach to explore the genomic characteristics of the released stocks and populations established 30 years (4-5 generations) after the release in two lakes down-stream of the release site.

Exploring the genomic dynamics of population hybridization and establishment in novel environments is becoming increasingly topical in the context of climate change effects and human induced population translocations. Salmonid fishes represent a group of species experiencing several such large-scale perturbations expected to affect microevolutionary processes. Here, two genetically separate brown trout populations are studied following their release into an environment previously void of this species. We use a pooled sequencing approach to explore the genomic characteristics of the released stocks and populations established 30 years (4-5 generations) after the release in two lakes down-stream of the release site. We find that even though extensive hybridization has occurred, the released stocks have contributed unequally to the descendant populations. While most of the differences between the released stocks can be attributed to drift, we identify regions of the genome that appear to have been under selection in the stocks' native environments. Most of these regions appear to be under balancing selection in the new environment. Genetic drift is the strongest force also in the new environment, but a few regions putatively under directional selection are identified, where genes from one of the released populations appear advantageous. The results demonstrate that hybridization, establishment, and adaptation can be rapid after release into novel environments. Such ongoing processes are important to follow for the conservation and management of populations. We show that they are possible to follow over microevolutionary time scales even for a species with relatively small local effective population sizes.

在气候变化影响与人类诱导的种群易地转移（population translocations）背景下，探究种群杂交与在新环境中定殖的基因组动力学特征，正成为日益受关注的研究热点。鲑形目鱼类（Salmonid fishes）是一类正经历多种此类大规模扰动的类群，这些扰动预计会影响微进化（microevolution）过程。本研究选取两个遗传分化的褐鳟种群，将其释放至此前无该物种分布的环境中，随后对其展开研究。我们采用混池测序（pooled sequencing）策略，对释放的亲本种群，以及释放位点下游两个湖泊中、于释放后30年（即4-5个世代）建立的种群的基因组特征展开探究。研究结果显示，尽管已发生广泛的杂交，但不同释放亲本种群对后代种群的遗传贡献并不均等。尽管释放亲本种群间的多数差异可归因于遗传漂变（genetic drift），但我们仍鉴定出了一些在亲本种群原生环境中曾受选择的基因组区域。其中多数区域在新环境中似乎处于平衡选择（balancing selection）作用之下。尽管遗传漂变仍是新环境中作用最强的进化力量，但我们仍鉴定出少量疑似处于定向选择（directional selection）作用下的基因组区域，其中一个释放种群的相关基因表现出适应性优势。本研究结果表明，在被释放至新环境后，种群的杂交、定殖与适应过程可快速发生。对这类持续发生的过程进行追踪，对于种群的保护与管理具有重要意义。本研究证实，即便对于局部有效种群大小（effective population size）相对较小的物种，也可在微进化时间尺度上对上述过程进行追踪。