Morphological and genetic evolution in eastern populations of the complex (Cypriniformes: Cyprinidae), with the descriptions of four new species.

For many years the North American cyprinid fish Macrhybopsis aestivalis (common name: Speckled Chub) was regarded as a single widespread and morphologically variable species, occurring in rivers throughout much of the Mississippi Valley and geographically adjacent eastern Gulf slope drainages, west to the Rio Grande basin in Texas, New Mexico, and Mexico. Eisenhour (1997) completed a morphological study of western populations of the Speckled Chub, the results of which appeared thereafter in published form (Eisenhour 1999, 2004). He demonstrated the existence of five valid species west of the Mississippi River (aestivalis, marconis, australis, tetranema, hyostoma), of which the name aestivalis was shown to be restricted to the population occurring in the Rio Grande and the geographically adjacent Rio San Fernando system, in northeastern Mexico.