Effect of Fish Dispersal Ability on Sensitivity to Habitat Fragmentation in a Large Lake

Habitat fragmentation negatively impacts natural processes, leading to reduction of genetic diversity, and is a major problem in conservation biology. Since the early 1800s, construction of ten major causeways in Lake Champlain has progressively divided the lake into several relatively isolated basins, providing a novel opportunity to study the consequences of whole-lake fragmentation on population restructuring of fish species. We took advantage of causeway fragmentation to test how barriers affect the genetic connectivity of fish species with different dispersal abilities. We sampled three coldwater fish species with different dispersal behavior: slimy sculpin (low dispersal), lake whitefish (medium dispersal), and rainbow smelt (high dispersal) from three distinct basins of Lake Champlain separated by causeways. We used molecular genetic techniques and Bayesian population mapping to identify population structure of each species and calculated genetic distance among basins within each species. Lake whitefish form three distinct populations in basins separated by causeways, suggesting that causeways do limit gene flow. Additionally, we found different allelic frequencies of rainbow smelt loci among basins, suggesting similar patterns of isolation. We anticipate similar patterns in slimy sculpin population structure. Our study tests the significance of dispersal power on species sensitivity to fragmentation in an aquatic system.