Systematics, Variation, and Speciation of the Macrhybopsis aestivalis Complex West of the Mississippi River
Systematics, Variation, and Speciation of the Macrhybopsis aestivalis Complex West of the Mississippi River. Bulletin of the Alabama Museum of Natural History, Number 23:9-47, 8 tables, 17 figures. The systematics of the Macrhybopsis aestivalis complex (Cypriniformes: Cyprinidae) has been unclear due to confusing morphological variation across the range of the complex. Prior to this study, only one species with six subspecies was recognized. Morphometry, meristics, pigmentation, and tuberculation were examined throughout the western half of the range of the complex. A taxonomic revision is presented with redescriptions of four species, a key to the described species, distributional data, comparisons, and evaluation of contact zones and geographic variation. Analyses of the morphological data support the recognition of five species west of the Mississippi River: M. aestivalis in the Rio Grande basin and Rio San Fernando drainage; M. man;ollis in the San Antonio, Guadalupe, and Colorado River drainages; M. australis in the upper Red River basin; M. tetrallema in the upper Arkansas River basin; and M. hyostoma widespread in the Mississippi River basin and in streams of the West Gulf Slope. Macrhybopsis hyostoma is sympatric with M. marcollis in the middle Colorado River mainstem, M. australis in the middle Red River mainstem, and M. tetra/lema in the central Arkansas River basin. Clinal variation along the length of the Rio Grande is exhibited by M. aestivalis, and considerable geographic variation is present in M. hyostoma. A phylogeny of the M. aestivalis complex was estimated from 17 morphological characters. The monophyly of the M. aestivalis complex, a sister relationship of M. australis and M. tetrallema, the monophyly of the remainder of the species of the M. aestivalis complex, and a sister relationship of M. sp. "Coosa chub" and M. sp. "Florida chub" each were supported by consensus and bootstrap trees and at least one character transformation free of homoplasy. Uncertain relationships among the remainder of the species may be attributed to considerable homoplasy among the characters used in the phylogenic analysis and a pattern of speciation by multiple peripheral isolates. Considerable morphological variation in M. hyostoma may be due to periodic isolation of eastern and western populations during Pleistocene glacial advances and adaptation to local environmental conditions.
Bulletin of the Alabama Museum of Natural History, Vol. 23, 9-48.