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...