USGS Columbia Environmental Research Center Project: Development of methods for the production of double haploid Scaphirhynchus sturgeon

Statement of Problem: The pallid sturgeon (Scaphirhynchus albus) was listed as federally endangered in 1990 and is currently the focus of intense recovery efforts.  The pallid sturgeon and the closely related, but more common shovelnose sturgeon (Scaphirhynchus platorynchus) are endemic to the Mississippi and Missouri Rivers and lower sections of their larger tributaries from Montana to the Gulf of Mexico.  Hybridization of the pallid sturgeon with the sympatric shovelnose sturgeon was identified as a substantial threat to the pallid sturgeon and was a factor in listing the species as endangered (Dryer and Sandvol, 1993).  Ongoing genetic and morphometric analyses of data from a multi-year study funded by the USFWS indicate that the level of genetic introgression increases with distance downstream in the Missouri and Mississippi Rivers (Dr. Edward Heist, Southern Illinois University-Carbondale,  written commun., 2016). Introgression is common in the Lower Mississippi River and field-identified pallid sturgeon collected there are predominately hybrids.  The extent of introgression in the Lower Mississippi River currently challenges the ability analytical techniques to identify pure specimens of pallid sturgeon and discriminate among potentially significant geographically distinct populations. Past studies have focused intensively on distinguishing the two species of Scaphirhynchus (Schrey and others, 2006) and little comprehensive effort has been placed on determining the frequency, extent or cause of hybridization and introgression between the two species (Schrey and others, 2011). It is unclear how long introgression has been occurring and whether the extent of introgression has increased due to anthropogenic factors. Thus, a multifaceted but concerted effort to address the issue of pallid sturgeon identification and hybridization range wide is needed.  Once Scaphirhynchus  sturgeon can be accurately assigned to either species or one of the various backcross permutations  of introgression, then quantitative testing of alternative hypothesis regarding hybridization can be undertaken to understand the past processes that have led to the present observed genotypic patterns in Scaphirhynchus inhabiting the Mississippi River Basin.  After processes have been elucidated, the threat of hybridization to pallid sturgeon can be assessed. Understanding the mode of hybridization, and assessing its threats will be important for future conservation efforts of pallid sturgeon.

Existing genetic discrimination between the species relies on 19 microsatellite loci markers (Schrey, 2007) and is made more cost-effective by the addition of a small number of single nucleotide polymorphic markers (Eichelberger and others, 2014).  This number of markers is insufficient to resolve differences between pure pallid sturgeon and individuals affected by generations of introgression (Schrey and others, 2011).  In the presence of high rates of introgression the current markers are insufficient to evaluate geographically distinct populations in the downstream most portion of the species' range.  The development of the large numbers of genetic markers needed requires the creation of homozygous double haploid specimens to eliminate the confounding effects of heterozygosity associated with polyploidy. This study will develop methods necessary to reliably create double haploid Scaphirhynchus sturgeon necessary to create the hundreds to thousands of genetic markers necessary to address questions surrounding pallid sturgeon population structure and hybridization.

Objectives: Develop methods to produce doubled haploid Scaphirhynchus sturgeon offspring carrying homozygous genomic DNA for genetic analyses and differentiation of both pallid sturgeon and shovelnose sturgeon.  This work is critical to detect and quantify introgressive hybridization between the two closely related species.
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