BULLETIN FLORIDA STATE MUSEUM


This mosaic pattern is not concordant with the normal expectation
for subspecies.

 2. Competition is, in effect, nonexistent between subspecies, and
where one has moved into a region formerly occupied solely by an-
other, intergrading populations occur. The presence of isolated
relict populations of cornutus surrounded by populations of chryso-
cephalus far to the south of the principal range, together with the
observed gradual replacement of cornutus by chrysocephalus in parts
of Ohio, indicate that competition exists where these fishes occur
together.

 3. Chrysocephalus apparently has disappeared from several mixed
populations in southern Michigan following construction of dams
near the mouths of the creeks where it formerly occurred. If cor-
nutus and chrysocephalus were only subspecifically distinct, the phe-
notypic character of the populations would be expected to remain
more or less constant.

 4. The experimentally-verified differences in temperature toler-
ance between cornutus and chrysocephalus in the northern limits of
their respective ranges are greater than one might normally expect
in subspecies. The apparent preference of cornutus for headwaters
and of chrysocephalus for the lower reaches of streams furnishes fur-
ther evidence of this difference.

 5. The distributional patterns of these forms suggest a long sepa-
ration of cornutus and chrysocephalus, ample to permit evolution to
the species level, and possibly dating back to late Pliocene.

 Raney's paper includes a discussion of the morphology, fertility,
hybrid vigor, and sex ratio of the cornutus X rubellus hybrids. He
decided, as did Hubbs and Brown (1929: 36-37), that hybridization
between these species is accidental, and usually results from simul-
taneous spawning over the nests of other species, such as Hybopsis
micropogon, Semotilus atromaculatus, and Exoglossum maxillingua.
In the absence of such nests rubellus and cornutus spawn in different
parts of the same riffle, rubellus in mid-water near the head, and
cornutus on the bottom toward the base. Milt from rubellus males
is washed downstream by the current, where it unites with eggs of
cornutus. The latter observations are similar to those of Moore and
Paden (1950: 92) for Notropis pilsbryi and Dionda nubila. Hybrids
of this combination apparently arise as a result of the simultaneous


Vol. 8