Abstract
Based on RAPD, the genetic structures of Stenopsyche marmorata, Hydropsyche orientalis, and Ephemerella nigra populations found above and below reservoirs with various water surface areas were investigated. The results of the genetic distance showed that amongst the six reservoirs, the genetic differentiations of H. orientalis were found in the third smallest and in the largest reservoirs while those of S. marmorata were shown in the two largest reservoirs. The size of reservoir influenced the genetic differentiations for S. marmorata, but did not for H. orientalis. The expected heterosygosity indicated that genetic diversities of H. orientalis were constrained by both effects of habitat fragmentation and population size while the rest of the species were constrained only by the latter's effect.
