Everything about Tilapiine Cichlid totally explained
| subdivision =
Alcolapia
Danakilia
Iranocichla
Oreochromis
Pelmatochromis
Pterochromis
Sarotherodon
Steatocranus
Stomatepia
Tilapia
Tristamella
}}
The
Tilapiini is a
tribe within the family
Cichlidae commonly known as
tilapiine cichlids. Most of the
taxa herein are called "
tilapias", a diverse and economically important group containing the
genera Oreochromis,
Sarotherodon and
Tilapia. A number of smaller genera, such as
Alcolapia,
Danakilia,
Iranocichla and
Steatocranus are also placed herein.
Systematics
The tilapiines were recognised by the
ichthyologist Ethylwynn Trewavas.
(External Link
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Recent
DNA sequence analyses, however, suggest that the Tilapiini as presently delimited are not
monophyletic. The
mtDNA study by Nagl
et al. (2001) and Klett & Meyer (2002) found that
Tilapia, in which formerly all tilapias were united, still seemes to constitute a
paraphyletic assemblage, composed of a
basal grade,
T. bemini which seems closer to
haplochromines, and a group containing for example
T. buttikoferi and
T. ruweti of presently unresolved relationships. The first group as well as
Iranocichla,
Oreochromis,
Sarotherodon and
Tristamella are fairly close to tribes such as the
Lamprologinii and
Tropheinii. Unfortunately, the
type species of
Tilapia (and hence, the tilapiines) doesn't seem to be among them.
mtDNA-based
phylogenies of tilapiines must be evaluated with caution however, as they're usually close to but do
not represent the true evolutionary relationships of these fishes. The reason is that
hybridization within any one of these major lineages is known to usually produce fertile offspring, and might also do so between the lineages.
Gene pools in these fishes have been kept (largely) separate by behavioral cues since millions of years, but reproductive incompatibility has been far slower to evolve, like in many
Pseudocrenilabrinae (African cichlids).(Nagl
et al. 2001)
A small
sample size—one to a mere handful of specimens per
taxon—as is often used in molecular studies further acerbates the problem. As discussed below for the example of
mouthbreeding, non-molecular data such as
morphology or
behavior has also turned out to be extremely prone to
homoplasies, not the least due to the small but ongoing
gene flow between evolutionarily quite distant gene pools.
Essentially, most traditional and mtDNA-based phylogenetic hypothesis for tilapiines must be considered with a high degree of caution. This problem could be alleviated to some extent by using
nDNA sequences. Comparing these with the mtDNA data, hybridization effects could be discerned. Also, it's likely that resolution of nDNA is still good enough to delimit the
clades that apparently exist in the "tilapiines" if numerous taxa and specimens are sampled. Researchers could then reanalyze morphological data to discover actual
autapomorphies.
Evolution seems to run quickly in this group. Even the fast-evolving mtDNA sequences often are incapable of properly resolving interspecies relationships (compare support values and proposed relationships in Nagl
et al. 2001 to Klett & Meyer 2002). It may be that the precise evolutionary history of some tilapiines can't be properly resolved with presently available methods, for the reasons discussed above.
Diversity of breeding behaviour
Like other cichlids, tilapiines exhibit complex reproductive behaviours and guard their eggs and fry. Broadly speaking, the
plesiomorphic trait is substratum-spawning behavior, meaning that the fish form pairs, lay the eggs on a rock or into a depression made in the substrate, and then both parents guard the eggs and fry.
Oreochromis and
Sarotherodon are
mouthbrooders, carrying the eggs and fry in their mouths instead of placing them in a nest. The numerous
Oreochromis species are maternal mouthbrooders, meaning that only the female looks after the eggs and fry, with the male offering no protection or help at all. Instead, they form
leks where they compete with one another for further opportunities to mate with females.
By contrast, most of the far fewer
Sarotherodon species are biparental mouthbrooders, with both parents protecting the eggs and fry. A few, such as
Sarotherodon melanotheron, are paternal mouthbrooders, with only the male caring for the eggs and fry. In addition, some species usually placed in
Oreochromis might belong into
Sarotherodon (Nagl
et al. 2001). Either this is incorrect due to hybridization effects, or they're not maternal mouthbrooders, or the diversity of brood care is even higher among the smallest group of tilapias than it was hitherto believed.
Further Information
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