Data from: Fine-scale population structure and riverscape genetics of brook trout (Salvelinus fontinalis) distributed continuously along headwater channel networks

Linear and heterogeneous habitat makes headwater stream networks an ideal ecosystem in which to test the influence of environmental factors on spatial genetic patterns of obligatory aquatic species. We investigated fine-scale population structure and influence of stream habitat on individual-level genetic differentiation in brook trout (Salvelinus fontinalis) by genotyping eight microsatellite loci in 740 individuals in two headwater channel networks (7.7 km and 4.4 km) in Connecticut, USA. A weak but statistically significant isolation-by-distance pattern was ubiquitous in both sites. In the field, many tagged individuals were recaptured in the same 50m-reaches within a single field season (summer to fall). One study site was characterized with a hierarchical population structure, where seasonal barriers (natural falls > 1.5 m in height) greatly reduced gene flow and weaker spatial patterns emerged due to the presence of tributaries, each with a group of genetically distinguishable individuals. Genetic differentiation increased when pairs of individuals were separated by high stream gradient (steep channel slope) or warm stream temperature in this site, although the evidence of their influence was equivocal. In a second site, evidence for genetic clusters was very weak at the most, but genetic differentiation between individuals was positively correlated with number of tributary confluences. We concluded that the movement of brook trout was limited in the study headwater streams, resulting in the fine-scale population structure (genetic clusters and clines) even at distances of a few kilometers, and gene flow was mitigated by “riverscape” variables, particularly by physical barriers, waterway distance (i.e., isolation-by-distance) and the presence of tributaries.线性且异质性的生境使得源头溪流（headwater stream）网络成为探究环境因子对专性水生物种（obligatory aquatic species）空间遗传格局影响的理想生态系统。本研究以美国康涅狄格州的两处源头河道网络（总长分别为7.7千米与4.4千米）中的740尾溪红点鲑（Salvelinus fontinalis）为研究对象，通过对8个微卫星位点（microsatellite loci）进行基因分型，探究了其精细尺度种群结构，以及溪流生境对个体水平遗传分化的影响。两处研究位点均普遍存在微弱但具有统计学显著性的距离衰减效应（isolation-by-distance）格局。野外调查期间，诸多标记个体在单个野外季（夏季至秋季）内被重捕于同一50米河段中。其中一处研究位点具有层级式种群结构特征：高度超过1.5米的自然跌水这类季节性障碍大幅降低了基因流（gene flow）；而支流的存在则催生了较弱的空间遗传格局，每条支流均拥有一组遗传特征可区分的个体。在该位点中，当个体对之间存在高溪流坡度（steep channel slope，陡峭河道坡度）或较高的溪流水温时，遗传分化程度会升高，尽管二者影响的相关证据尚存争议。在第二处研究位点中，遗传聚类（genetic clusters）的相关证据极不显著，但个体间的遗传分化与支流汇流数量呈正相关关系。本研究最终得出结论：溪红点鲑在研究区域的源头溪流中运动能力受限，即便在数千米的空间尺度下，也形成了精细尺度的种群结构（遗传聚类与渐变群（clines））；基因流会受到河流景观（"riverscape"）变量的调控，其中尤以物理障碍、河道距离（即距离衰减效应）以及支流的存在影响最为显著。