New genetic tools give a detailed picture of hybridization & population structure of Flannelmouth Sucker

Authors: Thomas Turner, Thomas Dowling, Abby Wicks, Guilherme Caeiro-Dias, Alexander Cameron, Megan Osborne

Year: 2023

Abstract

We adapted next-generation genetic screening tools to study hybridization and fine-scale population structure in Flannelmouth Sucker (Catostomus latipinnis) in two important Colorado River systems. We genotyped 1472 larvae distributed in two, 200-mile reaches in the Grand Canyon (GC) and San Juan River (SJR). We also genotyped 1085 adult fish sampled throughout the SJR mainstem and 300 adults that entered McElmo Creek, an intermittent tributary and an important spawning site for suckers. All sampled fish were identified as Flannelmouth Sucker based on morphology. Genetic analysis focused on hybridization status of individuals, and whether frequencies of hybrids were the same within and among river systems. Overall, 12% and 14% of larvae in the GC and SJR, respectively, had some evidence of introgression with Razorback Sucker (Xyrauchen texanus), with only marginal differences in frequencies across river systems. Introgressed larvae were randomly distributed in the GC, but not in the SJR. Larvae sampled downstream of McElmo Creek were more likely to be introgressed than larvae upstream. Adults in the SJR showed the same pattern, where adults sampled downstream of McElmo were more likely to be introgressed than upstream. We did not observe F1 or recently backcrossed hybrids in McElmo Creek, suggesting that hybridization with Razorback Sucker is probably occurring downstream. When all introgressed individuals were removed, reanalysis yielded two patterns of population structure. There was no obvious structure in the GC, but the SJR showed evidence of longitudinal differentiation up- and downstream, with hints of an unsampled spawning aggregation upstream.