Taxonomic Relationships of the Zuni Mountain Sucker, Catostomus discobolus yarrowi

Abstract

Catostomus discobolus yarrowi of the Little Colorado River drainage in New Mexico and Arizona is variable, populations morphologially and biochem­ ically intermediate between C. discobolus of the Colorado drainage and C. plebeius of the Rio Grande drainage. Specimens of C. yarrowi from the headwaters of the Little Colorado in the Zuni Mountains, New Mexico, are especially similar to populations of C. plebeius from just across the continental divide. Downstream populations are more like C. discobolus. Morphological and biochemical charac­ ters show slightly different trends among samples, but the patterns are consistent the hypothesis that a late Pleistocene stream capture resulted in introgres­ sion of C. plebeius characters into C. discobolus. I N 1874, E. D. Cope described Minomus jar­ rovii from the Zuni River headwaters of the Little Colorado River drainage in New Mexico, based on specimens 9 dorsal fin rays and the lower jaw with acute cartilaginous edge, regularly convex forwards. The types (USNM 15783) were collected by H. W. Hen­ shaw in 1873. (Cope gave the type locality as Provo, Utah, but Cope and Yarrow (1875) cor­ rected it to the Zuni River, New Mexico.) Fow­ ler (1913) referred to specimens from the same drainage, at Fort Wingate and Nutria, New Mexico, as Pantosteus plebeius, a species the above characters, living in the Rio Grande drainage. The populations were rediscovered in other Zuni tributaries by W. J. Koster: the Rio Pescado in 1948 and Nutria Creek in 1960. Smith (1966) showed that the Zuni River