Tuesday, June 5, 2007 - 11:15 AM
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Longitudinal relationships between genetic diversity and larval density of the caddisfly Hydropsyche orientalis

Kozo Watanabe, Ph.D1, Michael T. Monaghan, Ph.D2, and Tatsuo Omura, Ph.D1. (1) Department of Civil Engineering, Graduate School of Engineering, Tohoku University, Aoba 6-6-06, Sendai, Japan, (2) Entomology Department, Natural History Museum, Division of Biology, Imperial College London, SW7 5BD, London, United Kingdom

Small subpopulations may have low levels of genetic diversity, although widespread gene flow may counteract genetic drift and maintain high diversity. We examined the genetic structure of 15 subpopulations of the caddisfly Hydropsyche orientalis in the Natori River system in Japan using 78 polymorphic RAPD loci. Six subpopulations were fragmented by reservoirs and thus may be smaller, genetically isolated, or both. The aim of this study is to test whether genetic diversity in subpopulations was correlated with larval density and whether gene flow across the reservoirs was reduced. The percentage of polymorphic loci (%P = 46.3-59.1) and expected heterozygosity (Hexp = 0.163-0.225) both were positively correlated with larval density. There was a consistent unimodal pattern of longitudinal distribution with a peak of density and diversity in middle reaches. Pairwise Fst indicated reduced gene flow across the reservoirs (mean=0.219) relative to unfragmented streams (mean=0.157), but there was no consequent reduction of genetic diversity in these fragments. Our results suggest a possible extension of the river continuum concept that provides predictions for the longitudinal distribution of genetic diversity.