Yet Another “Splitter” – Genetic Diversity Reveals Cryptic Lamprey Species in Western North America

There are 41 described species of lampreys worldwide and more than half are non-parasitic, non-migratory brook lampreys.  However, the number of brook lamprey species has likely been underestimated since many isolated populations are considered the same species due to their conserved morphology.  For example, the western brook lamprey (Lampetra richardsoni) is commonly thought to occur along the west coast of North America from Alaska to California.  A second species – the Pacific brook lamprey (Lampetra pacifica) – was described in 1973 from Oregon and California, but has since been synonymized with L. richardsoni since the morphological differences between the two species were considered to be slight.  We therefore used mitochondrial cytochrome b gene sequences to better understand the phylogenetic and phylogeographic structure of the Lampetra species found throughout the Pacific drainage of North America.  This includes L. richardsoni and L. pacifica, the Kern brook lamprey (formally recognized as Entosphenus hubbsi but considered here as L. hubbsi since genetic data suggest it belongs to the genus Lampetra), and 36 unidentified Lampetra populations.  Additionally, since it is believed that non-parasitic brook lampreys evolved from parasitic species, the closely-related and parasitic river lamprey (L. ayresii) is included in the phylogeny.  Our results, using maximum parsimony and Bayesian analyses, do not correspond with any taxonomic scheme proposed to date.  Lampetra richardsoni as it is currently recognized is polyphyletic (i.e., consists of independently-derived populations), and although L. richardsoni and L. ayresii together constitute a well-supported clade distinct from several genetically-divergent populations in Oregon and California, they are not reciprocally monophyletic (e.g., all L. richardsoni are not more closely related to each other than some are to L. ayresii).  Furthermore, L. pacifica is excluded from the L. richardsoni-L. ayresii clade and the level of genetic divergence between L. richardsoni and L. pacifica (2.9-3.0%) is equivalent to that observed between L. richardsoni and L. hubbsi (which, as mentioned, is sufficiently distinct from L. richardsoni that it originally was placed in a different genus).  Although this provides support for the validity of L. pacifica as a distinct species, not all populations from Oregon and California occur within the L. pacifica clade.  Four additional populations in Oregon and California show genetic divergence between 2.2 and 6.5% from any known species (and up to 8.0% from each other), and may represent previously undescribed species.  This study thus represents an important first step towards identifying which populations require additional taxonomic study and protection.