- The minnow genus Siphateles is distributed throughout the Great Basin and adjacent drainages of western North America. Three species are currently recognized in the genus: S. alvordensis, Alvord chub, S. boraxobius, Borax Lake chub, and S. bicolor, the tui chub. S. bicolor has long been recognized as a widespread species exhibiting geographic variation. Relationships of Siphateles are investigated through phylogenetic analyses of mitochondrial cytochrome b gene sequences. Patterns of relationships within S. bicolor do not reflect current taxonomy. Sequence data support recognition of nine allopatrically distributed species currently recognized under S. bicolor: S. bicolor, S. columbianus, S. eurysomas, S. isolatus, S. mohavensis, S. newarkensis, S. obesus, S. thalasinnus and an unnamed species from Silver Lake, Oregon. Phylogenetic relationships resolved among these taxa indicate S. mohavensis forms the sister species to all remaining tui chubs. Relationships among remaining taxa were resolved as a polytomy of three species groups: an S. isolatus group containing S. isolatus + S. newarkensis; an S. bicolor group containing S. bicolor, S. columbianus, S. eurysomas, S. thalasinnus and Siphateles sp. (Silver Lake); and an S. obesus group, consisting of a polytomy of populations from California, Nevada and southcentral Oregon.
Examination of meristic and morphometric variation in the S. bicolor species group
supports recognition of species proposed by the molecular phylogenetic hypothesis. Oregon populations of S. obesus exhibit temporal variation in five scale-count
characters. Temporal variation occurred in all populations; comparisons among basins and three temporal groups (pre1958, 1975-1985 and 1993 collections) indicated approximately equal magnitudes of meristic variation in these two factors. No consistent trend to patterns of temporal variation was found, except within Summer Lake, where all mean scale counts were significantly different between pre1958 collections and 1975-1985 and 1993 collections. In addition, there was no correlation between mean meristic counts and average daily summer air temperatures. Consistent meristic differences in Summer Lake tui chubs may be due to the presence of S. thalassinus in this basin, either through hybridization or by biasing population characterization. Temporal variation in meristic characters is a widespread phenomena among tui chubs, and presumably among other fish species, in southern Oregon.