Phylogeographic and population genetic analysis of the barklouse Echmepteryx hageni

The eastern US barklouse species Echmepteryx hageni is primarily asexual, with two small, isolated sexual populations. Mitochondrial DNA sequences from the ND5 and 12S genes were analyzed from both phylgeographic and population genetic perspectives in order to investigate the evolutionary history of the species. The two sexual populations are nearly genetically identical, whereas the asexual E. hageni exhibited high levels of haplotypic diversity (H=0.9844). There is evidence of geographic structure at the entire tree level based on a Mantel test and nested clade analysis (NCA). NCA results also indicate a contiguous range expansion into Minnesota and Wisconsin. The distribution of pairwise differences fits the distribution expected under a model of sudden historical increase in population size. This conclusion is supported by tests of neutrality. The evolutionary relationship between sexuals and asexuals is unclear, as the root for the gene tree could not be established with confidence. The phylogenetic analysis suggests that the sexual populations may be derived, but further work is needed.