Abstract
The Least Chub (Iotichthys phlegethontis) is a small minnow endemic to the Bonneville Basin in Utah. Recently, new populations of Least Chub have been discovered in the upper Snake River in Idaho and in the San Pitch River downstream of Gunnison Reservoir in Utah. The objective of this study was to determine the likely origin of these newly discovered populations of Least Chub. We used genomic data to describe the genetic diversity of Least Chub from extant and refuge populations in Utah and from newly discovered populations. We assessed genetic variation between populations of Least Chub using restriction site-associated DNA sequencing. Despite low overall genetic diversity, our analyses indicated distinct population genetic structure between drainages and among geographic management units in Utah. Admixture analyses also showed distinct population structuring between groupings with little to no recent admixture. Overall, our results provide evidence that the Idaho Snake River populations and the Utah Gunnison population represent natural, distinct populations of Least Chub. The landscape for Least Chub conservation will need to change as we have provided evidence that the range of Least Chub is double the long-accepted range for the species. We recommend extensive surveys in both the Bonneville Basin and the upper Snake River drainage to further delineate the distribution of Least Chub and to identify new populations of the species.