Phylogeography of the Signal Crayfish Pacifastacus leniusculus in the Pacific Northwest

The signal crayfish Pacifastacus leniusculus is native to the Pacific Northwest region of North America, and has been well-studied as a prominent invasive species in Asia and Europe. However, many questions related to the ecology, management, taxonomy, and evolution of this species in its native range remain unresolved. We report results of an investigation into the phylogeography of P. leniusculus from throughout the Pacific Northwest using the mitochondrial 16S rRNA gene and morphological measurements. We evaluated distributional patterns and evolutionary relationships among the three historically recognized P. leniusculus subspecies (klamathensis, leniusculus, and trowbridgii), and sought to identify regions in the Pacific Northwest where P. leniusculus may have been introduced via live bait releases by anglers or deliberate stocking for harvest. For example, ecologists and resource managers have questioned whether P. leniusculus is native to Vancouver Island and other islands of the Salish Sea, where this species is implicated in declines of freshwater organisms. We found that extremely high genetic and morphological diversity characterize P. leniusculus throughout the Pacific Northwest, and we identified areas of apparent long isolation and potential cryptic diversity in this species. However, we also found evidence that P. leniusculus has been widely introduced throughout the region. These findings imply that managing P. leniusculus in the Pacific Northwest will be challenged by the need to identify some populations and subspecies of this crayfish as requiring conservation attention while also recognizing P. leniusculus as a potentially harmful invader in other regions within the same political jurisdiction. Our results underscore the importance of policies and regulations that discourage the transport and release of live crayfish in the Pacific Northwest both to protect unique populations as well as to discourage the potential spread of invasive P. leniusculus genotypes.