Gene flow and species delimitation in fishes of Western North America: Flannelmouth (Catostomus latipinnis) and Bluehead sucker (C. Pantosteus discobolus)

Abstract

2The delimitation of species-boundaries, particularly those obscured by reticulation, is a critical step in contemporary biodiversity assessment. It is especially relevant for conservation and 4 management of indigenous fishes in western North America, represented herein by two species with dissimilar life-histories co-distributed in the highly modified Colorado River (i.e., 6Flannelmouth Sucker, Catostomus latipinnis; Bluehead Sucker, C. Pantosteus discobolus). To quantify phylogenomic patterns and examine proposed taxonomic revisions, we first employed 8 double-digest restriction-site associated DNA sequencing (ddRAD), yielding 39,755 unlinked SNPs across 139 samples. These were subsequently evaluated with multiple analytical 10 approaches and by contrasting life history data. Three phylogenetic methods and a Bayesian assignment test highlighted similar phylogenomic patterns in each, but with considerable 12 difference in presumed times of divergence. Three lineages were detected in Bluehead Sucker, supporting elevation of C. P. virescens to species-status, and recognizing C. P. discobolus 14 yarrowi (Zuni Bluehead Sucker) as a discrete entity. Admixture in the latter necessitated a reevaluation of its contemporary and historic distributions, underscoring how biodiversity 16 identification can be confounded by complex evolutionary histories. In addition, we defined three separate Flannelmouth Sucker lineages as ESUs (Evolutionarily Significant Units), given 18 limited phenotypic and genetic differentiation, contemporary isolation, and lack of concordance (per the genealogical concordance component of the phylogenetic species concept). Introgression 20 was diagnosed in both species, with the Little Colorado and Virgin rivers in particular. Our diagnostic methods, and the alignment of our SNPs with previous morphological, enzymatic, and 22 mitochondrial work, allowed us to partition complex evolutionary histories into requisite components, such as isolation versus secondary contact. 24 (ESUs), as reflected by their reduced phenotypic and genetic differentiation. They thus lack concordance under the genealogical component of the phylogenetic species concept. 596 ACKNOWLEDGEMENTS 598Numerous agencies contributed field expertise, specimens, technical assistance, collecting permits, funding or comments for the completion of this study. We are in debt to students, 600 postdoctorals, and faculty who contributed to the development of our research:

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