Phylogenetic relationships of the North American sturgeons (order Acipenseriformes) based on mitochondrial DNA sequences

The evolutionary relationships of the extant species within the order Acipe nseriformes are not well understood. Nucleotide sequences of four mitochond rial genes (12S rRNA, COII, tRNA(Phe), and tRNA(ASP) genes) in North Americ an sturgeon and paddlefish were examined to reconstruct a phylogeny. Analys is of the combined gene sequences suggests a basal placement of the paddlef ish with regard to the sturgeons. Nucleotide sequences of all four genes fo r the three Scaphi-rhynchus species were identical. The position of Scaphir hynchus based on our data was uncertain. Within the genus Acipenser, the tw o Acipenser oxyrinchus subspecies were very similar in sequence and found t o be basal to the remaining Acipenser species examined. Based on our data, Acipenser transmontanus and Acipenser medirostris were sister tare, as were Acipenser fulvescens and Acipenser brevirostrum. Comparison of our results with hypotheses of sturgeon relationships proposed by previous authors is presented. The sequence data presented here are phylogenetically useful and provide a solid foundation of genetic information for the North American A cipenseriformes that can be expanded to include Eurasian species to provide a global picture of sturgeon evolution. (C) 2000 Academic Press.