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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

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.

Most of the hybrids were recognized as unusual at the time of capture, and were saved as part of numerically selective samples from the streams (rather than being discovered in the laboratory, in random samples).

Our measurements were made by methods defined by Hubbs and Lagler (1958); values are expressed as thousandths of the larger dimension.

=Chrosomus erythrogaster × Notropis cornutus frontalis=: KU 3872 (26.7 mm. in standard length) and KU 4170 (46.6 mm.) from Deep Creek, Riley Co., Kansas, Sec. 23, T. 11S, R. 7E, Dec. 14, 1957, and Apr. 26, 1958, respectively; and KU 4185 (39.3 mm.) from Bluff Creek, Pottawatomie Co., Kansas, Sec. 15, T. 6S, R. 8E, June 29, 1958. Compared in Table 1 with five specimens of C. erythrogaster, KU 3914 (39.3 to 47.3 mm., mean 43.0 mm.) from the same locality and of the same date as KU 3872 (above); and with five specimens of N. c. frontalis, KU 4184 (41.0 to 46.5 mm., mean 42.5 mm.) from the same locality and of the same date as KU 4185 (above). This cross has previously been recorded by Trautman (1957:326, 355) and by Minckley (1959:431).

The head-lengths of the hybrids are greater than in specimens of like size of C. erythrogaster or N. c. frontalis (Table 1). Hubbs and Miller (1943:373-374) reported that hybrids of Gila orcutti × Siphateles mohavensis have larger, more robust heads than either of the parental species, perhaps because of heterosis. The enlarged heads in hybrids of C. erythrogaster and N. c. frontalis result primarily from elongation of the postorbital region, with lesser elongation of the snout and orbit. The enlarged head affects measurements obtained for other structures that are parts of the head (and expressed as proportions of standard length or head-length), causing a tendency toward N. c. frontalis when the head-part is divided by standard length, and greater intermediacy or a tendency toward C. erythrogaster when the head-part is divided by head-length. In characters in which the parental species differ most (size of eye, length of upper jaw, and width of gape), the hybrids are intermediate between the parental species, regardless of whether the measurements are expressed as proportions of head-length or standard length; however, tendencies toward one or the other of the parental species (dependent on the divisor) can also been seen in these characters. Some experimentally propagated hybrids show highly variable, and sometimes extreme characters, rather than intermediacy of meristic and proportional characters (Hubbs, 1956).

TABLE 1. COMPARISONS OF THREE SPECIMENS OF CHROSOMUS ERYTHROGASTER × NOTROPIS CORNUTUS FRONTALIS WITH SPECIMENS OF THE PARENTAL SPECIES (MEANS ARE ABOVE, RANGES IN PARENTHESES BELOW)

=====================+=============+=============+=========+============== |Chrosomus erythrogaster | | KU 4170 and 4185 | | | KU 3872 | | | | Notropis | | | |c. frontalis ---------------------+-------------+-------------+---------+-------------- Standard lengths | 43.0 | 43.0 | 26.7 | 42.5 | (39.3-47.3) | (39.3-46.6) | ... | (41.0-46.5) | | | | Head-length / | 253 | 282 | 307 | 276 Standard length | (246-262) | (280-283) | ... | (273-283) | | | | Orbital length / | 067 | 075 | 101 | 083 Standard length | (063-071) | (071-079) | ... | (080-086) | | | | Orbital length / | 263 | 266 | 329 | 300 Head-length | (252-272) | (250-282) | ... | (291-310) | | | | Snout-length / | 069 | 073 | 071 | 068 Standard length | (068-071) | (071-075) | ... | (066-071) | | | | Snout-length / | 272 | 260 | 232 | 245 Head-length | (262-280) | (255-265) | ... | (233-260) | | | | Interorbital width / | 069 | 074 | 079 | 068 Standard length | (065-071) | (069-079) | ... | (067-069) | | | | Interorbital width / | 272 | 263 | 256 | 245 Head-length | (262-286) | (245-280) | ... | (241-250) | | | | Gape-width / | 056 | 065 | 064 | 065 Standard length | (051-059) | (059-071) | ... | (062-066) | | | | Gape-width / | 222 | 230 | 207 | 233 Head-length | (204-241) | (209-250) | ... | (224-239) | | | | Upper jaw-length / | 057 | 082 | 112 | 083 Standard length | (051-061) | (076-088) | ... | (080-086) | | | | Upper jaw-length / | 223 | 292 | 268 | 301 Head-length | (206-237) | (273-311) | ... | (284-315) | | | | Postorbital length / | 113 | 130 | 124 | 123 Standard length | (108-120) | (129-130) | ... | (121-125) | | | | Postorbital length / | 444 | 460 | 402 | 446 Head-length | (432-456) | (455-464) | ... | (431-457) | | | | Length of depressed | | | | dorsal fin / | 224 | 250 | 255 | 237 Standard length | (217-232) | (247-252) | ... | (233-243) | | | | Length of depressed | | | | dorsal fin / | 885 | 886 | 829 | 858 Head-length | (869-892) | (871-900) | ... | (836-890) | | | | Number scales in | | | | lateral line | 71.7 | 53.0 | 52(?) | 38.8 | (68-76) | (53.0) | ... | (38-39) | | | | Pharyngeal teeth | 0,5-5,0 | 1,5-4,1 | 1,5-4,2 | 2,4-4,2 | | ((?)-4,1) | | | | | | Anal rays | 8 | 8 | 8 | usually 9 | | | | Vertebrae | 37-40 | 39 | ... | 38-39 ---------------------+-------------+-------------+---------+--------------

In pigmentation, all three of the hybrids are intermediate between the parental species. The mid-lateral band (which is dark and discrete in C. erythrogaster, but faint, broad, and diffuse in N. c. frontalis) is broader and fainter in the hybrids than in Chrosomus, but is better developed than in N. c. frontalis. The dorsolateral dark band of C. erythrogaster is present in the hybrids, but is less distinct than in that species, and less distinct than the mid-lateral band of the hybrids themselves. The dorsolateral band is not present in N. c. frontalis. The color of the peritoneum in the hybrids is the glossy, jet-black of C. erythrogaster in two specimens, and the dusky-black of N. c. frontalis in one.

Chrosomus and Notropis differ greatly in the length and convolution of the intestine. Chrosomus has a long, coiled gut, which is crossed by the mid-ventral line eight or nine times; in N. c. frontalis, the intestine forms a flat, S-shaped loop that does not cross the mid-ventral line. In the two largest hybrids (KU 4170 and 4185), the gut is intermediate, crossing the mid-ventral line four times. In the smaller hybrid (KU 3872) the gut crosses the mid-ventral line twice but the configuration of the anterior loops indicates that the same intestinal convolutions that were found in the larger specimens would have developed in KU 3872 as the gut elongated with increase in size of the fish.

Both Deep and Bluff creeks are clear, gravel-bottomed streams draining parts of the Flint Hills Area of Kansas. A description of Flint Hills streams and lists of fishes occurring in them have been published by Minckley (1956 and 1959), and by Minckley and Cross (1959).

=Chrosomus erythrogaster × Semotilus atromaculatus=: KU 2947 (28.0 mm. in standard length) from Mill Creek, Wabaunsee Co., Kansas, Sec. 30, T. 12S, R. 9E, Mar. 22, 1953. Compared in Table 2 with five specimens of C. erythrogaster, KU 2836 (27.2 to 31.0 mm., mean 28.5) from the same locality and of the same date as KU 2947 (above); and with five specimens of S. atromaculatus, KU 1954, 2499, 2703, and 2838 (25.5 to 31.1 mm., mean 28.9 mm.) from streams in the same area.