An estimate of genetic and ecological influence on the coldwater-adapted freshwater fishes by artificially induced environmental alterlations in river systems

点击翻译按钮获取中文摘要

In oder to estimate the genetic and ecological influence on coldwater-adapted fishes by artificially induced environmental alterlations in river systems, the comparative studies on life-history characteristics and genetic population structure were carried out for some targetting fishes inhabiting the artificially-altered reaches and naturally-meandering reaches, and flowing results were obtained :(1) In the some rivers of southern Hokkaido Island, the population sizes, densities and habitat preferences of Lethenteron reissneri larvae were compared between those in artificially-straighten reaches by both the concrete-blocked banks and in naturally-meandering reaches. In consequence, the population sizes and densities of larvae were larger than those in the straitened reaches, mainly because more number of sandy-mud bottoms which were preferencially inhabited by the larvae were scattered in the former reaches. These results obtained from field survey and the other laboratory experiments … More of habitat preference suggest that Lethenteron reissneri larvae prefer to inhabit the sandy-mud bottoms composed of fine particle and deeper substrate.(2) In the Nishitappu River, which is located near Tomakomai City and has a big weir constructed in 1957 at the middle course of the river, the genetic population structure and life-history characteristics were compared between the downstream anadromous population and the upstream river-resident population of threespined stickleback, Gasterosteus aculeatus. As the result, a significant difference was found in the allozymic gene frequency between the two populations. The upstream river-resident population showed smaller body size and higher age composition at breeding season than the downstream anadromous population. These results demonstrate that the land-locked population has evolved genetically and ecologically from the ancestral anadromous stock for about 40 years after the construction of weir.(3) In three rivers of southern Hokkaido Island, the genetic variability within populations and genetic divergence among populations were compared using microsatellite DNA gene markers between the downstream anadromous and upstream river-resident populations of white-spotted charr, Salvelinus leucomaenis, which were separately distributed by dams. Consequently, the river-resident forms showed about 70% low mean heterozygosities, compared to those in the anadromous forms. Furthermore, the FST values (0.02-0.225) between the anadromous and river-resident forms clearly demonstrated that the latter forms were genetically divergent from the former forms. Statistic analyses indicate that the extent of genetic divergence between the two forms were positively correlated with the years for which the river-resident forms had been isolated from the anadromous forms, and negatively correlated with the whole waterflows in respecive rivers.(4) On the basis of present study, artificially environmental alterations of river structures such as straightness of river courses and construction of weirs or dams are concluded to influence negatively on the biodiversity in coldwater-adapted fishes. Less