Hatchery propagation & augmentation slow, but do not prevent, genetic erosion in Rio Grande Silvery Minnow

Authors: Megan Osborne, Guilherme Caeiro-Dias, Thomas Archdeacon, Robert Dudley, Charles Yackulic, Thomas Turner

Year: 2022

Abstract

Strategic planning and successful conservation of imperiled species require accurate information about demographic trends. Monitoring genetic effective population size (Ne) has also been widely advocated in conservation programs because it is an important predictor of adaptive potential. Genetic (microsatellites and single nucleotide polymorphisms [SNPs]) and demographic monitoring data of wild-born and augmented fish, spanning the most recent megadrought (2000–2022), were used to examine relationships between estimated abundance and contemporary Ne in the endangered Rio Grande Silvery Minnow, Hybognathus amarus. Estimates of the fraction of the population comprised of augmented fish were significantly correlated with genetic estimates of gene flow between these population components. Estimates of variance effective population size (NeV) of the entire population (augmented and wild-born) were less than estimates of wild-born NeV. This result shows that augmentation serves as an additional source of genetic drift. Analysis of temporal divergence shows a shift in allele frequencies after the 2012–2014 drought-induced population bottleneck. When a greater fraction of the population comprised hatchery fish, genetic effective size was reduced. Extending analyses to SNP-based microhaplotypes revealed recent reductions in observed heterozygosity and increases in inbreeding metrics. Together, our results show that hatchery propagation and augmentation slow, but do not prevent, genetic erosion in Rio Grande Silvery Minnow.