Spatial and temporal changes in genetic structure and diversity of isolated white-spotted charr (Salvelinus leucomaenis) populations

Abstract

In Japan, numerous artificial dams constructed for erosion control or hydroelectric power generation have affected almost all rivers and resulted in isolation and fragmentation of many freshwater fish populations. We examined genetic structure and diversity of two temporally isolated samples (spanning 15 years) from 23 white-spotted charr (Salvelinus leucomaenis) populations, including above- and below-dam populations, on Hokkaido Island. We used microsatellite DNA markers to elucidate how habitat fragmentation by damming can spatiotemporally alter population genetic structure. An isolation-by-distance genetic structure was found for anadromous populations on Hokkaido Island, which indicates substantial gene flow among populations. After habitat fragmentation by damming, isolated populations were indiscriminately subjected to genetic differentiation from anadromous (below-dam) populations within river systems, and to the subsequent loss of genetic diversity. Effective population sizes of isolated populations were less than 50. We found that substantial decreases in heterozygosity and allelic richness occurred in some isolated white-spotted charr populations over 15 years. This study shows that habitat fragmentation by damming induces significant spatial changes in population genetic structure and genetic diversity within river systems. Our findings also provide an important implication that most isolated white-spotted charr populations will continuously lose genetic diversity in the future.