Data from: Self-sustaining populations, population sinks or aggregates of strays: chum (Oncorhynchus keta) and Chinook salmon (O. tshawytscha) in the Wood River system, Alaska

Small populations can provide insights into ecological and evolutionary aspects of species distributions over space and time. In the Wood River system in Alaska, USA, small aggregates of Chinook (Oncorhynchus tshawytscha) and chum salmon (O. keta) spawn in an area dominated by sockeye salmon (O. nerka). Our objective was to determine whether these Chinook and chum salmon are reproductively isolated, self-sustaining populations, population sinks that produce returning adults but receive immigration, or strays from other systems that do not produce returning adults. DNA samples collected from adult chum salmon from 16 streams and Chinook salmon from four streams in the Wood River system over 3 years were compared to samples from large populations in the nearby Nushagak River system, a likely source of strays. For both species, microsatellite markers indicated no significant genetic differentiation between the two systems. Simulations of microsatellite data in a large source and a smaller sink population suggested that considerable immigration would be required to counteract the diverging effects of genetic drift and produce genetic distances as small as those observed, considering the small census sizes of the two species in the Wood River system. Thus, the Wood River system likely receives substantial immigration from neighbouring watersheds, such as the Nushagak River system, which supports highly productive runs. Although no data on population productivity in the Wood River system exist, our results suggest source–sink dynamics for the two species, a finding relevant to other systems where salmonid population sizes are limited by habitat factors.

小型种群可为解析物种在时空尺度上的分布特征及其生态与进化层面的相关机制提供关键研究视角。在美国阿拉斯加州的伍德河水系（Wood River system）中，奇努克鲑（Chinook salmon，Oncorhynchus tshawytscha）和大麻哈鱼（chum salmon，O. keta）的小型集群会在以红大马哈鱼（sockeye salmon，O. nerka）为优势种的区域产卵。本研究旨在明确该水系中的奇努克鲑与大麻哈鱼究竟属于三类群体中的哪一类：一是生殖隔离且可自我维持的独立种群；二是仅能产出洄游成体但依赖外源个体迁入的种群汇（population sink）；三是源自其他无法产生洄游成体的水系的迷游个体。本研究采集了3年间伍德河水系内16条溪流的成年大麻哈鱼以及4条溪流的成年奇努克鲑的DNA样本，并将其与邻近的努沙加克河水系（Nushagak River system）的大型种群样本进行比对——后者被认为是迷游个体的潜在来源。针对两个物种，微卫星标记（microsatellite marker）分析结果显示，两处水系之间未检测到显著的遗传分化。基于大型源种群与小型种群汇的微卫星数据进行的模拟分析表明：考虑到伍德河水系内两个鲑鱼物种的实际普查种群规模较小，若要抵消遗传漂变的分化效应并达到观测到的遗传距离水平，需要相当规模的外源个体迁入才能实现。因此，伍德河水系很可能从邻近流域（如高产洄游种群支撑的努沙加克河水系）获得了大量的外源个体迁入。尽管目前尚无伍德河水系的种群生产力相关数据，但本研究结果表明这两个鲑鱼物种存在种群源-汇动态（source–sink dynamics），这一发现对于其他受生境因素限制鲑科鱼类（salmonid）种群规模的水系具有参考意义。