The family Acipenseridae consists of 25 extant sturgeon species (19 species of Acipenserinae and 6 species of Scaphirhynchinae). Together with two extant paddlefish species, Polyodon spathula and Psephurus gladius (Polyodontidae), it composes the order Acipenseriformes, the most numerous of all living "fossil" fishes. This paper presents results of sequencing of three regions of the cytochrome b gene (650 bp), and fragments of 12S (150 bp) and 16S (350 bp) rRNA genes, from all extant species of Acipenserinae (species of Acipenser and Huso) and Scaphirhynchus albus (Scaphirhynchinae). The phylogenetic tree obtained for combined data is the first comprehensive treatment of phylogeny within the Acipenserinae. Three general conclusions are inferred from the tree: (1) The pallid sturgeon, S. albus, is the sister-species of all species of Acipenser and Huso. (2) The two species of Huso are embedded within the genus Acipenser. It also appears that Huso is not a separate taxonomic unit. (3) There are at least three main clades within Acipenser: A. sturio-A. oxyrinchus, A. schrenckii-A. transmontanus, and all Ponto-Caspian species plus A. dabryanus and A. brevirostrum. There is congruence between ploidy and the branching patterns of the sturgeon species. A hypothetical evolutionary history of the Acipenseriformes based on the paleontological, geological, and molecular data is discussed. (C) 1998 Academic Press.
