Evolutionary Relationships of the Plagopterins (Teleostei: Cyprinidae) from Cytochrome b Sequences
Sequences of cytochrome b (cytb) were used to examine composition and phylogenetic relationships of cyprinid fishes of the tribe Plagopterini, endemic to the Great Basin and Lower Colorado River in southwestern North America. The plagopterin genera, Lepidomeda, Meda, Plagopterus, and Snyderichthys, were most closely affiliated with the chubs Couesius and Margariscus of northern and eastern North America. As indicated by previous morphologic, allozymic, and mtDNA studies, Snyderichthys is intimately related to Lepidomeda. The relationship is paraphyletic, however, according to our molecular data. Snyderichthys from the Snake and Bear River drainages are part of a clade that includes Lepidomeda mollispinis and Lepidomeda albivallis according to the cytb sequence, with Snyderichthys from the central and southern Bonneville basin more divergent. This paraphyly and the complex geographic relationships of mtDNA sequences indicate a complex history of the group and cast doubt on the validity of morphologically diagnosed Snyderichthys. Estimates of divergence time, based on a combination of fossil and molecular data, indicate that the plagopterins are an ancient clade, at least 17 million years old.Abstract
Approximate distribution of species and samples (indicated by lines and shading). Snyderichthys copei, Goose Creek (SCGC), Sulphur Creek (SCSC), Spanish Fork River (SCSF), Sevier River (SCSR); Lepidomeda albivallis (LA), Lepidomeda mollispinus mollispinus (LMM), Lepidomeda mollispinus pratensis (LMP); Lepidomeda vitatta (LV); Plagopterus argentissimus (PA); Meda fulgida, Verde River (MFV), Aravaipa Creek (MFA). The southwest range limits of the sister groups, Couesius plumbeus and Margariscus margarita, are shown in the upper right
Scatter of pairwise sequence divergences against time since initial divergence [millions of years (Ma)], as estimated from first appearance of diagnostic apomorphy in the fossil record (from Table 2). Lines identify regressions unconstrained (solid, R2 = 0.48) and forced through the origin (dashed, R2 = 0.44), yielding estimated divergence rates of 0.53% and 0.66%/lineage/ma, respectively
Results from parsimony analysis of cytb sequences. Unweighted and weighted analyses produced similar results; therefore, only the more resolved topology (weighted) is presented. This topology represents a strict consensus of six most-parsimonious trees with transversions given twice the weight of transitions. Numbers above and below branches identify bootstrap values (percent) from unweighted and weighted analyses, respectively. Bootstrap values not provided are less than 60%
Neighbor-joining tree generated by clustering gamma corrected Tamura-Nei distances (alpha = 0.3). Numbers by branches identify bootstrap values (percent). Only bootstrap values ≥ 70% are shown. Scale represents number of substitutions/site