Produced by Chris Curnow, Erica Pfister-Altschul, Joseph Cooper and the Online Distributed Proofreading Team at http://www.pgdp.net [Transciber's Note: The follow suspected error has been corrected in this text: Page 3: _C. erythogaster_ changed to _C. erythrogaster_] UNIVERSITY OF KANSAS PUBLICATIONS MUSEUM OF NATURAL HISTORY Volume 13, No. 1, pp. 1-18 June 1, 1960 Five Natural Hybrid Combinations in Minnows (Cyprinidae) BY FRANK B. CROSS AND W. L. MINCKLEY UNIVERSITY OF KANSAS LAWRENCE 1960 UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY Editors: E. Raymond Hall, Chairman, Henry S. Fitch, Robert W. Wilson Volume 13, No. 1, pp. 1-18 Published June 1, 1960 UNIVERSITY OF KANSAS Lawrence, Kansas PRINTED IN THE STATE PRINTING PLANT TOPEKA, KANSAS 1960 [Illustration] 28-3424 Five Natural Hybrid Combinations in Minnows (Cyprinidae) BY FRANK B. CROSS AND W. L. MINCKLEY The hybrid fishes described herein are _Chrosomus erythrogaster_ (Rafinesque) × _Notropis cornutus frontalis_ (Agassiz), _C. erythrogaster_ × _Semotilus atromaculatus_ (Mitchill), _Campostoma anomalum plumbeum_ (Girard) × _S. atromaculatus_, _Gila nigrescens_ (Girard) × _Rhinichthys cataractae_ (Valenciennes), and _Notropis venustus venustus_ (Girard) × _Notropis whipplei_ (Girard). Two of the combinations have been reported, without descriptions, in literature (citations below), and Hubbs (1955: Fig. 3) graphically indicated hybridization between the same genera with which this paper is concerned, but did not designate the species involved. All specimens of _C. erythrogaster_ × _N. c. frontalis_, _C. erythrogaster_ × _S. atromaculatus_, _C. a. plumbeum_ × _S. atromaculatus_, and _N. v. venustus_ × _N. whipplei_ were taken in a period of severe drought in Kansas and Arkansas. All were from small, spring-fed streams that support large populations of fishes. That the drought of 1953-1956 had pronounced effects on stream habitats in Kansas has been documented by Minckley and Cross (1959). Satisfactory sites for spawning may have been few, but an abundance of adult fishes persisted from earlier, wet years. Unusual crowding of spawning fishes would increase the opportunity for fertilization of the eggs of one species by sperm from another species. We think that the hybrids reported here (excepting _G. nigrescens_ × _R. cataractae_) are explainable on the basis of crowding; we have no information about stream-conditions where the last-named hybrid was found. Generally, hybridization of fishes seems most common in areas that have been subject to radical climatic change in the past 20,000 or fewer years (Hubbs, 1955:18-19), and in streams that have been altered recently by the activities of man (Hubbs and Strawn, 1956:342, and others). Streams from which we report hybrids probably were affected by overgrazing of their watersheds; overgrazing was unusually severe in the drought.