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

Abstract

The goal for this project was to re-examine key morphological characters hypothesized to differentiate Gila intermedia, Gila robusta and Gila nigra and outline methods better suited for making species designations based on morphology. Using a combination of meristic counts, morphological measurements and geometric morphometrics, morphological dissimilarities were quantified among these three putative species. Traditional meristic counts and morphological measurements (i.e. distances between landmarks) were not useful for species identification. Geometric morphometrics, however, identified differences among species, while also suggesting an effect of geographic location on morphological variation. Using canonical variate analysis for the 441 fish sampled in this study, geometric morphometrics accurately predicted true group membership 100% of the time for G. nigra, 97% of the time for G. intermedia and 91% of the time for G. robusta. These results suggest that geometric morphometric analysis is necessary to identify morphological differences among the three species. Geometric morphometric analysis used in this study can be adopted by management officials as a tool to classify unidentified individuals.

Peer Review #1 of "Geopolitical species revisited: genomic and morphological data indicate that the roundtail chub Gila robusta species complex (Teleostei, Cyprinidae) is a single species (v0.1)"

“…However, the CVA resolved two separate groups of G. robusta and appears to be driven by geographic location rather than by evolutionary relationships. The two locations that overlap between Moran et al (2017) and the data presented here show that the G. robusta from the Verde River fall out in clade 1 and Aravaipa Creek appear in Clade 3 (Figure 2, 3) in our data. We find no evidence to support the validity of Gila robusta, G. intermedia, and G. nigra under any of the more prominent species concepts (i.e.…”

“…Type material for each of the currently recognized species of the G. robusta complex as well as the type of the G. robusta synonym G. grahamii were obtained from the Smithsonian Due to the problems associated with the taxonomic key (Moran et al, 2017;Carter et al, 2018) the current practice of species identification for managers and researchers working with the G. robusta complex within the Lower Colorado River Basin is based on drainage location, as assigned by Rinne (1969) and later revised by Minckley and Demarias (2000). We follow this RNA Later (ThermoFisher Scientific, Waltham, MA) for reduced representation genomic sequencing using the ezRAD protocol (Toonen et al, 2013;Knapp et al, 2016).…”

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

“…Until recently, the consensus was defined by Minckley and DeMarais (2000) on the basis of morphometric and meristic characters. 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.…”

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

“…Numerous molecular studies have attempted to resolve the relationships of the Gila robusta complex. Although interpretations of the data vary, there is no clear evidence to date that the three nominal species of Gila in the drainages of the Lower Colorado River basin represent reproductively isolated and distinct evolutionary units ( DeMarais, 1992 ; DeMarais et al, 1992 ; Dowling & DeMarais, 1993 ; Schönhuth et al, 2012 , 2014 ; Dowling et al, 2015 ; Marsh, Clarkson & Dowling, 2017 ), nor has a reliable method (morphological or molecular) of assigning individual fish to species been identified ( Moran et al, 2017 ; Carter et al, 2018 ). The current practice of species identification for managers and researchers working with the G. robusta complex requires identifications based on collection locality as determined by Rinne (1969) and later revised by Minckley & DeMarais (2000) based on mean morphological differences of populations rather than diagnosable morphological or molecular characters of individuals, because no such characters have been identified.…”