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Résumé :
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Reservoirs have the potential to block the gene flow of stream macroinvertebrates along a Received 27 February 2006 channel, which takes place via larval drift and adult flight, resulting in genetic differentiation Received in revised form above and below the reservoirs. Gene flow across the reservoirs may be strongly obstructed if 15 November 2006 the area of standing water is larger. Using random amplified polymorphic DNA markers, we Available online 17 January 2007 investigated the genetic structure of Stenopsyche marmorata (Stenopsychidae: Trichoptera) populations found above and below the reservoirs, and the reference stream of six reservoirs Keywords: with small to large water surface area ranging from 0.12 km(2) to 6.00 km(2). As a result, the two largest reservoirs with a standing water area larger than 3.27 km(2) showed significant differ flow ences in pairwise 0 between fragmented and reference streams, whereas the other four res fragmentation ervoirs with a standing water area smaller than 1.64 km(2) showed insignificant differences. Genetic diversity The genetic differentiations in the two largest reservoirs did not result in the reduction of Population size genetic diversities in the fragments. Based on the significant correlation between relative population size and mean expected heterozygosity, we concluded that local genetic diversities were constrained in smaller populations due to the effect of genetic drift. (C) 2006 Elsevier Ltd. All rights reserved.
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