Abstract

The freshwater diaptomid copepod Hesperodiaptomus shoshone (S.A. Forbes, 1882) occurs in high altitudes of Western North America, ranging from British Columbia to Colorado in the Rocky Mountains, and in the Sierra Nevada of California. I examined the genetic variation of H. shoshone at different spatial scales to determine the extent of current demographic processes and historical events shaping the distribution and dispersal of this species. First, I examined the phylogenetic relationships within the genus Hesperodiaptomus based upon nuclear ribosomal DNA gene sequences. Phylogenetic reconstructions supported the monophyletic origin of the genus and revealed two clades supported by morphological characters. Second, I carried out a phylogeographic study using partial DNA sequences of the cytochrome oxidase I gene and from nuclear ribosomal DNA gene sequences from 51 populations representing the current distribution range of the species. The genetic divergence among populations was high, and indicates a low level of dispersal among populations. The data revealed the presence of two geographically distinct deep lineages (North/South), with further genetic sub-structuring within each region. I hypothesize that the observed patterns of genetic diversity and structure reflect historical dispersal events and episodic range displacement due to glaciations. Finally, I characterized three microsatellite markers for this species and carried out a population genetic study to examine the genetic structure among 12 neighbouring populations in the Gunnison area of Colorado. The results indicated that H. shoshone have significant population differentiation and high genetic divergence suggesting a limited gene flow even at relatively small spatial scales.