Benthic communities and genetic structure of caddisfly stenopsyche marmorata along a mountain stream fragmented by slit and unslit sabo dams

Abstract

In order to assess the impacts of sabo dam (check dam) construction, species diversity of benthic faunal communities and genetic diversity of caddisfly Stenopsyche marmorata were investigated using microsatellite analysis along the Oisawa River, Japan. The Oisawa River is fragmented by two slit sabo dams and one unslit sabo dam. Over the slit dams, Shannon-Weiner diversity indices and number of taxa ranged from 0.90 to 1.02 and 13 to 15 respectively in the upstream region, and also from 0.98 to 1.18 and 13 to 20 respectively in the downstream region. Through microsatellite analysis of S. marmorata, we found two selective alleles, which show clear genetic differentiation among three upstream sites and four downstream sites in the study area. Longitudinal change of mean heterozigosities Ho showed a decreasing pattern of genetic diversity in the downstream site (=0.486 - 0.678), and it showed the highest diversity at the highest upstream site, which receives no effect of the unslit dam. Differences of community's species compositions between sites were correlated to geographical distances whereas genetic distances between sites were not correlated to geographical distances, suggesting that species compositions of the communities were determined through the process of species adaptation to the local environment. We concluded that increments of species diversity at the inlet reaches of the slit dam were caused by the recovery of habitats, and by the continuousness of the stream which allows the flowing of particulate organic matters and sediments to the downstream area. In part of some loci, genetic selection might occur by the different velocities caused by sabo dam constructions, because S marmorata (filter-feeder) has the habit of constructing nets to filter and collect fine particulate organic matter (FPOM) from water flow. © 2011 WIT Press.