Open Access PDF - Sven Kullander

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mented, apparently mucus-filled, circular area
slightly posterior to the nostril and at the dorsal
margin of the nasorbital depression. This area
represents probably a free neuromast; it can be
probed into the skin, but does not seem to represent
an opening to the nasal sac, instead it may
be related to the multiple perforations connecting
to the anterior nasal lateralis canal opening. Preliminary
observations suggest that this character
is also present in other cichlids.
Geographical distribution. Most species of Cichla
now known conform to a general pattern of
allopatric distribution, although several species
are sympatric or even syntopic. This suggests that
Cichla is a component of a general species distribution
pattern in tropical South America. Limiting
factors are sometimes obvious, with elements
of isolation to or above major rapids (C. thyrorus,
C. melaniae, C. mirianae, C. jariina), restriction to
certain water conditions, e.g., blackwaters (C. temensis,
C. orinocensis) or clearwater rivers (C. piquiti,
C. melaniae, C. mirianae, C. thyrorus, C. jariina),
as is known from other cichlids. The historical
patterns are more obscure. The species pattern
does not retrace that of other cichlid genera and
the tree (Fig. 93) shows a complex geographic
branching.
Essentially, the distribution of the genus recovers
the Guianan and Brazilian highlands. Cichla
monoculus is exceptional in its wide floodplain
distribution in the western Amazon basin, but
there is too little information about the fish fauna
of tributaries to conclude if it is really restricted
to floodplains. Cichla monoculus extends eastwards
to the mouth of the Amazon and occurs also in
the Oyapock drainage. It is represented by similar
species in Bolivia (C. pleiozona) and the Rio
Tocantins (C. kelberi). Cichla ocellaris is the only
species occurring in several rivers in the Guianas,
but also in the Rio Branco. The putative sister
species is C. nigromaculata in the upper Orinoco
and Negro rivers.
Cichla vazzoleri and C. pinima occur in tributaries
below major rapids east of the Rio Negro and
Rio Madeira, but restricted to opposite sides of
the Rio Amazonas. Cichla from the Amapá are
identified as C. pinima, but based on limited material.
Two species, C. orinocensis and C. temensis
are distributed over two major river drainages,
the Negro and the Orinoco, which, however, are
incompletely separated being connected across
the Rio Casiquiare. Cichla ocellaris is recorded from
both the Rio Branco and several rivers in Guyana
and Suriname.
Species of Cichla are remarkably similar to
each other in body proportions and most meristics.
Colour variation provides the best species
diagnostic characters. In this regard Cichla conforms
to other genus-level taxa of cichlids in South
America, which are morphologically distinct, but
within each genus species differ principally in
colour pattern. Since cichlids are diurnal, and
effect an elaborate behaviour including visual
clues in social interaction, this is not surprising.
More surprising is that other morphological differentiation
tends to be limited. Possible explanations
could be that the generic subdivisions among
cichlids are biased towards recognizing units
separated by morphological gaps, that morphological
key innovations are functional in stable
communities not permitting radiating evolution,
or biased or incomplete character sampling.
Clearly, patterns of variation in colour and
meristics are easier to perceive than other aspects
of the type of organisms represented by Cichla
and other cichlids. Silfvergrip (1996), working
with a genus of nocturnal catfishes over the entire
Neotropics, found surprisingly few species in a
total analysis approach, where others have easily
described species by comparing just selected
geographical samples. The conclusion is that
colour variation greatly facilitates species recognition.
Whereas genera of cichlids are recognized
by gaps, phylogenetic morphological and molecular
analyses support about the same branching
patterns of genera (e.g., Kullander, 1988;
Farias et al., 2001), and it thus seems likely that
morphological characters are reasonably well
sampled and consequently genera are reasonable
approximations of monophyletic morphologybased
clades. Clearly, ecological functional constraints
may be the most plausible explanation
for the pattern shared by Cichla and other cichlid
genera with a more or less consistent allopatry of
included species – whenever there is vicariance
followed by speciation, colour divergence is the
most obvious marker of speciation. It is hard to
think that all intrageneric cichlid speciation would
represent very recent isolation, with insufficient
time for further differentiation.
Under this functional constraint hypothesis,
changes in characters not affecting the basic body
plan and consequently feeding ecology, would
have little effect on the ecological function of the
new species, but mutations relating to the com-
Kullander & Ferreira: Review of Cichla