Geopolitical species revisited: genomic and morphological data indicate that the roundtail chubGila robustaspecies complex (Teleostei, Cyprinidae) is a single species

Abstract

The Gila robusta species complex in the Lower Colorado River Basin has a complicated taxonomic history. Recent authors have separated this group into three nominal taxa, G. robusta, G. intermedia, and G. nigra, however aside from location, no reliable method of distinguishing individuals of these species currently exists. To assess relationships within this group, we examined morphology of type specimens and fresh material, and used RADseq methods to assess phylogenetic relationship among these nominal species. Maximum likelihood and Bayesian inference tree building methods reveal high concordance between tree topologies based on the mitochondrial and nuclear datasets. Coalescent SNAPP analysis resolved a similar tree topology. Neither morphological nor molecular data reveal diagnostic differences between these species as currently defined. As such, G. intermedia and G. nigra should be considered synonyms of the senior G. robusta. We hypothesize that climate driven wet and dry cycles have led to periodic isolation of population subunits and subsequent local divergence followed by reestablished connectivity and mixing. Management plans should therefore focus on retaining genetic variability and viability of geographic populations to preserve adaptability to changing climate conditions.

Taxonomic Uncertainty and the Anomaly Zone: Phylogenomics Disentangle a Rapid Radiation to Resolve Contentious Species (Gila robusta complex) in the Colorado River

“…Because anomalous gene trees are most probable under a scenario of rapid radiation (as documented herein), the reduced number of loci used by Schwemm (2006) could not recover a consistent species tree. Copus et al (2016Copus et al ( , 2018 examined a dataset containing 6,658 genomic SNP loci (across 1,292 RAD contigs), but only did so across a sparse sample of individuals. A bioinformatic acquisition bias also likely impacted this study, in the form of strict filtering that disproportionately excluded loci with higher mutation rates (Huang and Knowles 2016).…”

“…These have since proven of limited diagnostic capacity in the field, thus provoking numerous attempts to re-define morphological delimitations (Brandenburg et al 2015;Moran et al 2017;Carter et al 2018). Genetic evaluations have to date been inconclusive (Schwemm 2006;Copus et al 2018), leading to a recent taxonomic recommendation that subsequently collapsed the complex into a single polytypic species (Page et al 2016(Page et al , 2017.…”

Can members of the south‐western Gila robusta species complex be distinguished by morphological features?

“…robusta in middle sections of a single stream. The American Fisheries Society and the American Society of Ichthyologists and Herpetologists Joint Committee on the Names of Fishes, however, recently investigated the taxonomic status of species in the robusta complex and, based on preliminary whole‐genome sequence data (Copus et al ., ), determined the available genetic and morphological data supports a single species rather than three (Page et al ., ). Within this context, it is important to note that G .…”

Brown trout phylogenetics: A persistent mirage towards (too) many species

“…Willis, 2017), suckers (Bangs et al, 2020), topminnows (Duvernell et al, 2019) and coregonids (Coregonus ardeti species flock; Ackiss et al, 2020). Based on several thousand polymorphisms, Copus et al (2018) proposed reducing the Gila robusta complex to a single species. NGS data also provided a better assessment of origin, colonization routes, demographic histories including admixture and introgression, and/or identification of stage of divergence during the speciation process in diverse fish species (e.g., Fang et al, 2018;Jeffries et al, 2016;Lucek et al, 2018;Ravinet et al, 2018;Rougemont & Bernatchez, 2018).…”