Systematics, taxonomy, and conservation status of sturgeon in the subfamily Scaphirhynchinae (Actinopterygii, Acipenseridae)

Sturgeon in the subfamily Scaphirhynchinae are imperiled worldwide. Recognition of biodiversity within this group is paramount to any successful conservation or recovery efforts. A series of qualitative characters and univariate and multivariate analyses of morphological data were employed in three studies to uncover species diversity within Scaphirhynchinae. In the first study, a phylogenetic analysis of Acipenseridae using morphological characters corroborates the monophyly of the subfamilies Acipenserinae and Scaphirhynchinae. Within Scaphirhynchinae, the North American genus Scaphirhynchus is monophyletic but the central Asian genus Pseudoscaphirhynchus is paraphyletic. Scaphirhynchus albus is the sister group to S. platorynchus and S. suttkusi. Scaphirhynchus suttkusi is an endangered species endemic to the Mobile Basin. Reevaluation of the taxonomic status of this species using additional data and alternative analyses supports S. suttkusi as a distinct species. The second study addresses the possible hybridization between the endangered S. albus and the sympatric S. platorynchus within the Mississippi River Basin, presumably due to habitat modifications. Several character indices have been developed to identify these parental species and their hybrids. Specimens of assumed pure S. albus and S. platorynchus, and crosses between these species, all propagated, raised, and preserved at hatcheries, were used to test these indices. Existing indices fail to correctly identify the species and known hybrids for all size classes. However, principal components analysis provides complete separation of species and hybrids and demonstrates that F1 hybrids are intermediate morphologically with respect to parental species. The final study examines intraspecific variation within all three currently recognized species of Pseudoscaphirhynchus , a genus of sturgeon endemic to the Amu Darya and Syr Darya rivers of the critically imperiled Aral Sea Basin. The two forms within P. kaufmanni and P. hermanni and the three forms within P. fedtschenkoi are distinct species diagnosable on the basis of morphological data. These seven species of Pseudoscaphirhynchus have different life history strategies, abundances, and threats. Recognition of these distinct evolutionary species is critical for accurate conservation assessments and recovery efforts.