The phylogeny of lampreys: An assessment based on the gene order and nucleotide sequence for the mitochondrial genomes of Geotria australis and Mordacia mordax

Phillipa Louise Milton

Lampreys are jawless fish whose earliest ancestor is believed to have diverged from other jawless fishes at least 500 million years ago. The 38 contemporary members of the group are commonly allocated to three families, that is, Petromyzontidae (34 species found in temperate latitudes of the Northern Hemisphere), Mordaciidae (3 species found in temperate latitudes of the Southern Hemisphere) and Geotriidae (one species found in temperate latitudes of the Southern Hemisphere). Whilst recent molecular studies suggest that lampreys are more closely related to another group of extant jawless fish, that is, hagfishes, than they are to jawed vertebrates, the interrelationships of the three families of lampreys has yet to be resolved. In this study, 15 776 nucleotides for the mitochondrial genome of Geotria australis (Geotriidae) and three separate fragments of 4134, 1616 and 1294 bp in length, totalling 7044 bp for Mordacia mordax (Mordaciidae) were sequenced. Analyses of the genomes revealed characteristics consistent with other animal mitochondrial genomes. Maximum parsimony analyses of individual and concatenated protein-coding genes at both the nucleotide and amino acid level, for the Southern Hemisphere lamprey species G. australis and M. mordax, in combination with published sequence data from the Northern Hemisphere lamprey species, Petromyzon marinus and Lampetra fluviatilis, resolved the three-taxon statement regarding the relationships of the Petromyzontidae, Mordaciidae and Geotriidae. The outgroup taxa included two gnathostomes (Mustelus manazo and Oncorhynchus mykiss) and two hagfishes (Myxine glutinosa and Eptatretus burgeri). The results demonstrated that lampreys are a monophyletic group, the Petromyzontiformes, and that the Petromyzontidae, Mordaciidae and Geotriidae constitute three further monophyletic groups. Furthermore, the Petromyzontidae and Geotriidae were more closely related than either was to the Mordaciidae, which was the most basal oflamprey families.

The phylogeny of lampreys: An assessment based on the gene order and nucleotide sequence for the mitochondrial genomes of Geotria australis and Mordacia mordax

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