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Phylogeographic methods involve determining the historical relationships among gene lineages with attention to the contemporary spatial distribution of those lineages. In other words, the methodology entails deriving a gene tree for an array of individuals and/or taxa and then mapping that tree onto the geographic localities whence the individual DNA samples were collected. By so doing, one can potentially examine the effects of putative geographic barriers to gene flow. If geographic samples are reciprocally monophyletic with respect to a putative geographic barrier (Fig. 1a), then that barrier is often inferred to have inhibited the dispersal of individuals and their genes. If, on the other hand, the geographic samples are not reciprocally monophyletic (Fig. 1b), then we can infer either that the barrier is not a barrier at all, or that the barrier arose too recently yet to be recorded in the genetic data. Because these methods have a concern both for spatial patterning of individual alleles, and for their historical relationship to other homologous alleles, phylogeography has emerged as the theoretical bridge that unites the traditionally distinct fields of phylogenetics and population genetics (Avise et al., 1987; Avise, 1989). To date, phylogeographic studies have focused primarily on mitochondrial DN