Influences of geologic history and climatic factors on the phylogeographic structure of two sucker species in Arizona’s Little Colorado River drainage

Authors: Derek Houston, Ashley Hurst, Cristian Román-Palacios, Mark Grover, Dennis Shiozawa

Year: 2024

Abstract

Western North America has a complex geological and climatological history that has greatly influenced the evolution of its resident native fishes, resulting in high levels of endemism for numerous species and phylogroups. Recent research suggests that Bluehead Sucker, Pantosteus discobolus, and Flannelmouth Sucker, Catostomus latipinnis, both exhibit pronounced genetic diversity, and possible cryptic diversity, in Arizona’s Little Colorado River drainage. We used a reduced-representation genomic data set to assess population genetic structure within both species’ native ranges. More specifically, we addressed three research questions: 1) Do Bluehead Sucker populations exhibit pronounced phylogeographic structure? 2) Do Flannelmouth Sucker populations exhibit pronounced phylogeographic structure? 3) Do these sucker species exhibit genetic signatures of introgressive hybridization? Our results show that Grand Falls, a large waterfall on the Little Colorado River, approximately 169 km upstream from the confluence of the Little Colorado River and the Colorado River, is a barrier to gene flow for Bluehead Suckers and Flannelmouth Suckers. We observed varying levels of genetic admixture among populations (of both species) above and below Grand Falls. Some populations show little to no admixture, whereas others contain high numbers of “hybrid” individuals. This is particularly the case with the Zuni Bluehead Sucker, Pantosteus discobolus jarrovii, where two of the three sampled populations have introgressed with Rio Grande Sucker, Pantosteus plebius. Populations of Bluehead Sucker and Flannelmouth Sucker above Grand Falls meet criteria for designation as Evolutionarily Significant Units.