Tilapiine cichlid

Taxobox
name = Tilapiine cichlids


image_width = 240px
image_caption = Zebra tilapia ("Tilapia buttikoferi") in an aquarium
regnum = Animalia
phylum = Chordata
classis = Actinopterygii
ordo = Perciformes
familia = Cichlidae
subfamilia = Pseudocrenilabrinae
tribus = Tilapiini
tribus_authority =
subdivision_ranks = GeneraVerify source|date=July 2007
subdivision ="Alcolapia" "Danakilia" "Iranocichla" "Oreochromis" "Pelmatochromis" "Pterochromis" "Sarotherodon" "Steatocranus" "Stomatepia" "Tilapia" "Tristamella"
synonyms =Tilapiinae

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. They are nowadays placed in the subfamily [Pseudocrenilabrinae] of African cichlids; forrmerly thes were often regarded as a distinct subfamily Tilapiinae.

ystematics

The tilapiines were recognised by the ichthyologist Ethylwynn Trewavas. [http://www.safarilands.org/index.php/wildlife/more/frequently_asked_questions_on_tilapiine_cichlids/]

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 presentlyVerify source|date=July 2007 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) does not seem to be among them.

mtDNA-based phylogenies of tilapiines must be evaluated with caution however, as they are 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 mightVerify source|date=July 2007 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 is 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 cannot 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 are not maternal mouthbrooders, or the diversity of brood care is even higher among the smallest group of tilapias than it was hitherto believed.

References

* (2002): What, if Anything, is a Tilapia? Mitochondrial ND2 Phylogeny of Tilapiines and the Evolution of Parental Care Systems in the African Cichlid Fishes. "Molecular Biology and Evolution" 19(6): 865–883.
* (2001): Classification and Phylogenetic Relationships of African Tilapiine Fishes Inferred from Mitochondrial DNA Sequences. "Molecular Phylogenetics and Evolution" 20(3): 361–374. doi|10.1006/mpev.2001.0979
* (1983): "Tilapiine fishes of the genera "Sarotherodon", "Oreochromis" and "Danakilia. Published by the British Museum (Natural History), London. 583 pages. ISBN 0-565-00878-1