Phenotype predicts genotype for lineages of native cutthroat trout in the southern Rocky Mountains

Authors: Kevin R. Bestgen, Kevin B. Rogers, Robert Granger

Year: 2014 (xlvi)

Abstract

Morpho-meristic characteristics of cutthroat trout Oncorhynchus clarkii were described from 48 populations in the Rio Grande, and Colorado, South Platte, and Arkansas River basins in Wyoming, Colorado, Utah, and New Mexico. These include presumptive Rio Grande (O. c. virginalis), Colorado River (O. c. pleuriticus), and greenback (O. c. stomias) cutthroat trout subspecies and the unusual Bear Creek, Colorado, population. Our main goal was to determine if phenotypes of individuals and populations, first assigned to lineages with mitochondrial DNA techniques, corresponded better to the subspecies recognized in the traditional Geographic Classification Model or to lineages under the newer Molecular Classification Model. Ten morpho-meristic characters, including scale, gill raker, and basibranchial tooth counts, as well as spot distribution and density patterns, were variable across taxa and discriminant function classification analyses better supported assignment of populations to the Molecular Model (90% correctly classified) than the Geographic Model (78% correctly classified). Bear Creek and Rio Grande lineages were distinct, as were Blue Lineage populations of the Upper Green River Basin. Green Lineage populations of the Colorado, Gunnison, and Dolores River drainages, as well as Front Range populations from the Arkansas and South Platte River drainages, were more difficult to classify and may represent more than one taxonomic entity. Classification success was also high within lineages at the drainage basin scale, suggesting smaller-scale organization of diversity. All lineages are rare and findings will be useful to managers tasked with listing decisions and conservation actions for these cutthroat trout.

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