Population Genetic Structure of Nebraska Paddlefish Based on Mitochondrial DNA Variation

—Eighty-three paddlefish Polyodon spathula that were collected from 1995 to 1999 from the Missouri River Galvins Point Dam tailwater were analyzed for genetic variation in the mitochondrial DNA d-loop region. Additional samples from Montana, South Dakota, and Louisiana were used for comparative purposes. To facilitate the efficient analysis of numerous paddlefish samples, we applied a method that employs polyacrylamide gel electrophoresis (PAGE) to resolve restriction fragment length polymorphisms (RFLPs) amplified by polymerase chain reaction (PCR). DNA sequencing of 10 paddlefish revealed 22 polymorphic sites. Polymerase chain reaction–RFLP analysis of 93 paddlefish using three restriction enzymes detected six of the polymorphic sites and revealed six distinct haplotypes. All of the observed haplotypes were found in the Missouri River Galvins Point Dam tailwater. No temporal differentiation was observed among the 1995, 1998, and 1999 samples from the Missouri River Galvins Point Dam tailwater. Polymerase chain reaction–RFLP, resolved with PAGE, provided an efficient method for population genetic analysis of paddlefish. The paddlefish Polyodon spathula Walbaum is an ancient fish that is native to the Missouri River, the Mississippi River, and several Gulf Coast drainages of North America (Gengerke 1986; Russell 1986). Paddlefish populations have declined along with a reduction in their range because of impoundment channel alterations and overharvesting (Gengerke 1986; Russell 1986). On the Missouri River, dams have interrupted migration routes and flooded or fragmented critical habitats (Unkenholz 1986). The decline of paddlefish populations has caused them to be listed as a species of concern in several states (Johnson 1987); they were also listed in the Convention on International Trade in Endangered Species in 1992 (Allardyce 1992). A report of the National Paddlefish and Sturgeon Steering Committee (1993) identified the loss of genetic variation as one of the committee’s primary concerns. However, information about * Corresponding author: [email protected] Received August 23, 1999; accepted January 27, 2000 paddlefish population genetic structure is incomplete. Previous allozyme studies (Carlson et al. 1992; Fries and Hutson 1993; Epifanio et al. 1996) and mitochondrial DNA (mtDNA) restriction fragment length polymorphism (RFLP) analysis (Epifanio et al. 1996) revealed low levels of allozyme allelic and mtDNA haplotype variation within and among paddlefish populations sampled from up to nine tributaries (Epifanio et al. 1996). The biochemical and molecular methods previously employed are not optimal for genetic analysis of numerous alcohol-preserved, field-collected samples. The objective of this study was to characterize mtDNA d-loop genetic variation from temporally sampled paddlefish collected from the Missouri River Galvins Pt. dam tailwater. Additional populations isolated by geographical range or by dams were included for comparative purposes. To facilitate the efficient analysis of numerous paddlefish samples, we have applied a method that employs polyacrylamide gel electrophoresis (PAGE) to resolve RFLPs amplified by polymerase chain re-