7146

• UCREFRP Catalog Number: 7146
• Author: Hubbs, C. L. and R. R. Miller
• Title: Hybridization in Nature Between the Fish Genera
• USFW Year: 1953
• Copyright Material: YES

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208

Hubbs and Miller

Hybridization between Catostomus and Xyrauchen

209

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peduncle, Haring caudal fin, long lips with seriated papillae, large
fins, and other features indicate that one parental species in the
upper river system is C. latipinnis rather than C. commersoni suck-
lel/i Girard or C. catostomus griseus Girard, both of which have re~
cently been transplanted there from the Mississippi watershed.
The species of Catostomus that hybridizes with Xyrauchen in the
Gila River system is presumed to be C. insignis for two reasons:
(1) C. insignis was taken with the hybrids and Xyrauchen, and (~)
the hybrids s~ow specific points of intermediacy between C. insignis
and X. texanus. They differ significantly from the C. latipinni.', X
X. texanus hybrids from the upper Colorado system. Thus the
caudal peduncle in the C. insignis X X. texanus hybrids is deeper
on the average than in X. texanus, as expected, since C. ins ignis
has a deeper peduncle than X. texanus (Table VII), wher~as the C.
lati:pinnis X X. texanus specimens have a slenderer peduncle than
in X. texanus, again as expected, since C. latipinnis has the slen-
derest peduncle of any of the forms involved (Table V; PI. I). In
thi'i respect the hybrids of the two combinations are strikingly un-
~ik(:: in the C. in.~ignis X X. texanus hybrids the peduncular depth
IS .093-.099 of the standard length; in the other hybrid combina-
tion it is .076-.083. Similar contrast is shown in the number of
sca les, which is lowest in C. insignis and highest in C. latipinnis
with the averages intermediate in each hybrid combination (Tabl~
II).
That the other parental species in both areas is the huge hump-
back sucker, Xyrauchen texanus (Abbott), admits of no reasonable
dou.bt, for the hybrids exhibit, in diluted form, some of the unique
features of that bizarre fish, including its great nuchal hump.
Xymuchen is one of the several genera of fishes that are endemic to
the Colorado River system (Miller, 1946a).
. The possibility that the fish here interpreted as hybrids may
Instead represent a distinct species, uncompahgre, intermediate
between Catostomus and Xyrauchen, or that they maybe referable to
two such species, seems excluded by circumstantial evidence. Fish
of this type have been collected only four times, a sin'gle specimen
twiee and six specimens twice. These collections have been well'
separated, spatially as well a.s temporally (1889, 19~6, 1947, and
1950). Furthermore, these aberrant specimens agree with known
hybrids not only in exhibiting characters intermediate between those

of the inferred parental species, but also, as noted above, in being
specifically intermediate between the particular local forms of the
parental genera. Furthermore, in certain respects, such as the
number of scales and the ,structure of the lips, the hybrids between
C. latipinnis and X. texanus are far more variable than we would
expect a species to be.
The criteria adopted in recognizing these new natural hybrids,
the methods followed in accumulating and analyzing the data, and
the style accepted in presenting the material are essentially the same
as those employed by Hubbs, Hubbs, and Johnson (1943, pp. 11-14,
63-73).
We thank Dr. Leonard P. Schultz and his staff for wholehearted
cooperation in our studies of pertinent specimens in the United
,States National Museum (U.S.N.M.). Material recently collected
in Utah by Dr. W. F. Sigler has proved of critical value. He,
along with Dr. Samuel Eddy, of the University of Minnesota
(U.M.), and Dr. William M. Lewis, of Southern Illinois University,
have cooperated in providing specimens which had been distributed.
The other material used is in the University of Michigan Museum
of Zoology (U.M.M.Z.). Robert L. Wisner took some of the X-ray
photographs. William L. Cristanelli drafteo the graphs and took
some of the photographs. Laura C. Hubbs has again contributed
her services, especially in the computations.

Catostomuslatipinnis X Xyrauchen texanus

(Pis. I-III)

U.S.N.M., No. 7599~: one wholly immature male 10~ mm. in
standard length, the holotype and only reported specimen of X yr-
auchen uncompahgre Jordan and EverIDann (in Jordan, 1891, pp.
~6-~7, pI. 5, fig. 1~), collected by David S. Jordan, Barton W. Ever-
mann, and party in Uncompahgre River close to Delta, Colorado;
August 14, 1889.
U.S.N.M., No. 143594: one wholly immature female ~56 mm.
long, seined by Preston and Dorothy Knoch in the Colorado River
one-half mile below Fruita Bridge, Mesa County, Colorado; Sep-
tember, 1947.
U.M.M.Z., No. 16~334 (five specimens), and U.M., No. 1634~
(one specimen): two emaciated males 385 and 391 mm. long, with