Demographic and Evolutionary History of Pallid and Shovelnose Sturgeon in the Upper Missouri River

Abstract

Abstract Natural-origin Pallid Sturgeon Scaphirhynchus albus in the upper Missouri River are predicted to become extirpated as early as 2024. To aid in recovery efforts for this endangered species, we used genetic data from 17 microsatellite loci to infer demographic and evolutionary history of Pallid Sturgeon and a sympatric Shovelnose Sturgeon S. platorynchus. Our data indicated a recent sundering of geneflow between these species by overlapping allele size distributions at all loci and low level of genetic divergence (FST = 0.10). Tests for recent bottlenecks by using heterozygosity excess or allele frequency mode-shift tests indicated demographic stability for both species, while the M ratio identified that historic bottlenecks occurred in both species. Estimates of historical effective population size (Ne), based on coalescent modeling of allele size distribution, suggested that the geographic expansion of these species into the upper Missouri River during the late Pleistocene was associated with 10- to 19-fold reductions in Ne. By contrast contemporary estimates of Ne based on linkage disequilibrium revealed that Shovelnose Sturgeon (Ne = 2,983) had approximately 10 times greater Ne than Pallid Sturgeon (Ne = 254). Our results are consistent with the recent collapse of Pallid Sturgeon being caused by dam construction, which occurred between 1930 and 1965. Fortunately, genetic diversity remaining in this long-lived species provided an opportunity to conserve predam Pallid Sturgeon genetic diversity via a successful captive breeding program. We provide recommendations to address key conservation needs, including how to incorporate our estimate of Ne/adult census size of 0.26 (95% confidence interval of 0.16–0.47) into setting demographic recovery goals for Pallid Sturgeon.