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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Three measurements were taken of the depth, but these are to a
laqe degree independent expressions, though correlated. The
greatest body depth (graph not reproduced) varies with condition as
well as size, but the plotted measurements clearly separate the
pal ental species, and the hybrids are intermediate. The depth
through the insertion of the pectoral fin measures primarily the
e1eration of the nuchal hump, which is diagnostic of Xyrauchen and
is partly developed in the hybrids (PIs. I and III). The depth of
the caudal peduncle differs noticeably in ecological forms, much more

10 20 30 40
120 J--LLJ

DEPTH THROUGH INSERTION
OF PECTORAL FIN

SO

100

thaI I does the greatest body depth. In some of the largest hybrids
the depth values approach those of Catostomu,~ latipinni,~, probably
beclLuse they are more 01' less emaciated. This emaciation affeds
least; the depth through the pectoral insertion, for the hump has a
bon.'1 base. In this character there is no overlap between the meas-
l~J'eI:1ents for t.he pa~ental species, and the values for the hybrids
he very close to the Ime of separation.
) n the overall length of the lips-an extremely variable charac-
ter, as Rutter (1908, pp. 123-24) pointed out for Catostomus occi-
dentalis-the hybrids are intermediate, but six approach C. latipinnis

Hybridization between Catostomus and Xyrauchen

217

~ .

much more closely and fall within the upper limit of variation for
that parental species. In the basal separation of the lower lips, most
of the hybrids come closer to C. latipinnis. Of the six large hybrids,
one falls outside of the growth curve for latipinnis, three resemble
that species more than they do Xyrauchen texanus, one is almost
precisely intermediate, and one comes much nearer to Xyrauchen.
In the width of the gape the hybrids are more variable: some speci-
mens resemble C. latipinnis and others closely approach X. texanus,
while still others are intermediate. Since the lip is longer and the
gape is narrower in C. latipinnis, the difference between the parental

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o "~o 0 x
o 0 0 0
o 0 0 000 0 0
o 0

x
x
iYoo

GAPE WIDTH
LIP LENGTH

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~Cb
o 0

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50

20

30

40

50

60

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10

FIG. 8. Change with age in the ratio of gape width to lip length (overall length of both
lips) in Cafostomus latipinm's (circles) and Xyrauche1! texanus (solid dots), and the
ratios of the eight hybrids (crosses). Computed from measurements plotted on
l<'igurt' 1.

species is accentuated by expressing the gape width as a p~rcenta~e
of the lip length (Fig. 3). In this proportion, as well as m the lip
structures, some of the hybrids approach X, texanus; others, C. lati-
pinnis. The variation is greater than would be expected within a
species. .. .
The gill rakers of the smallest hybrid are defimtely mtermedIate
in lcngth, as would be expected, since the giIlraker lengths of the
parental species differ in the young (Fig. 1). When four additional
measurements of Xyrauchen (taken after Fig. 1 was drawn) are
added, the distinction of the adults in respect to raker length largely