WILLIAMS: CHASMODES TAXONOMY


background of oyster shell or aquatic grasses. The greenish color of adult
males blends with the algae covering the oyster shells and aquatic grasses.
This cryptic coloration probably helps to protect the male from predation,
and thus indirectly protects the eggs being guarded during the spawning
season. The dark and light mottled color pattern of the females and
younger fishes is also cryptic and aids in concealment.
 Chasmodes bosquianus longimaxilla is known from Pensacola, Florida,
westward to the Texas coast and southward to Veracruz, Mexico. Very few
specimens of C. b. longimaxilla are known from Pensacola, and I believe
these are stragglers to the area. Large aggregations of C. b. longimaxilla are
encountered around oyster shell laden regions in Mobile Bay, Alabama,
where very few C. saburrae occur. The zone of sympathy of C. b. longi-
maxilla and C. saburrae extends from Pensacola, Florida, where C. sabur-
rae predominates, to the Chandeleur Islands, Louisiana. Individuals found
in this zone exhibit no overlap in diagnostic characters and show almost
exclusive segregation by habitat. Based on my collections in Mobile Bay
and ecological data on preserved specimens, C. saburrae appears to be
restricted to the grassbeds, whereas C. b. longimaxilla is associated with the
oyster reef community. This habitat specificity does not seem to hold
outside the zone of sympatry, allopatric populations of both species being
found in either of the two communities.
 The habitat specificity in the zone of sympathy is coupled with charac-
ter displacement in Chasmodes bosquianus longimaxilla. The populations
of C. b. longimaxilla in the zone of sympatry, although exhibiting a wide
range of maxillary lengths (14 to 22.5% SL), tend to have longer maxillary
lengths than other populations of this subspecies (Table 8). This difference
may be due to habitat segregation in the zone of sympatry. There is a
tendency for the maxillary length to decrease with increasing geographic
distance from the zone of sympathy (Table 8). This decrease is not statisti-
cally significant until the populations at either end of the geographic range
(excluding Veracruz) are compared (Table 7). This type of variation
provides support for the existence of an east-west dine in the northern Gulf
of Mexico. One possible explanation for this dine is that it is the result of the
effect of character displacement on the gene pool in the zone of sympatry,
together with a decreasing impact of this gene pool on increasingly distant
populations. Biochemical studies of these populations are needed to either
confirm or refute this hypothesis.
 Bath's (1977) report of two specimens of Chasmodes bosquianus (= C.
b. longimaxilla) from Veracruz, Mexico, constitutes the only record from
waters south of Laguna Madre, Texas. It is likely that additional specimens
will be collected from the northeastern coast of Mexico when these areas
are more intensively sampled. Although not reported in the few ichthy-
ofaunal studies done in this region (e.g. Resendez 1970, 1973), it should be


1983