Tilapiine cichlid
Encyclopedia
The Tilapiini is a tribe
within the family Cichlidae commonly known as tilapiine cichlids. Most of the taxa herein are called "tilapia
s", 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 Africa
n and Middle East
ern cichlids; formerly these were often regarded as a distinct subfamily Tilapiinae.
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. mtDNA studies 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 Tristramella
are fairly close to tribes such as the Lamprologini
and Tropheini
. 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 might also do so between the lineages. Gene pool
s 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).
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. It may be that the precise evolutionary history of some tilapiines cannot be properly resolved with presently available methods, for the reasons discussed above.
Oreochromis
and Sarotherodon
are mouthbrooder
s, 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. 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.
Tribe (biology)
In biology, a tribe is a taxonomic rank between family and genus. It is sometimes subdivided into subtribes.Some examples include the tribes: Canini, Acalypheae, Hominini, Bombini, and Antidesmeae.-See also:* Biological classification* Rank...
within the family Cichlidae commonly known as tilapiine cichlids. Most of the taxa herein are called "tilapia
Tilapia
Tilapia , is the common name for nearly a hundred species of cichlid fish from the tilapiine cichlid tribe. Tilapia inhabit a variety of fresh water habitats, including shallow streams, ponds, rivers and lakes. Historically, they have been of major importance in artisan fishing in Africa and the...
s", a diverse and economically important group containing the genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Oreochromis
Oreochromis
Oreochromis is a large genus of tilapiine cichlids, fishes endemic to Africa and the Middle East. Several species from this genus have been introduced far outside their native range, and are important in aquaculture...
, Sarotherodon
Sarotherodon
Sarotherodon is a genus of tilapiine cichlids, fishes endemic to Africa and the Middle East. A few species from this genus have been introduced far outside their native range, and are important in aquaculture. They mainly inhabit fresh and brackish water, but a few can live in salt water...
and Tilapia
Tilapia (genus)
Tilapia is a large genus of cichlid fishes endemic to Africa, except for a single species that also occurs in the Middle East. The vast majority of the species are from tropical Western and Middle Africa, but there are also a few species in Northern, Eastern and Southern Africa...
. A number of smaller genera, such as Alcolapia
Alcolapia
Alcolapia is a genus of fishes in the Cichlidae family. Their native range is largely restricted to the hypersaline, warm Lake Natron and Lake Magadi in Kenya and Tanzania, although two species also have been introduced to Lake Nakuru.-Species:...
, Danakilia
Danakilia
Danakilia is a genus of cichlid fish containing two species, namely Danakilia franchettii from the saline Lake Giulietti in Ethiopia, and Danakilia dinicolai from the saline Lake Abaeded in Eritrea....
, Iranocichla
Iranocichla
Iranocichla hormuzensis is a species of mouthbrooding fish from the cichlid family. It is the only member of its genus, and reaches a length of about . It is restricted to freshwater and brackish habitats in southern Iran. It is the only species of cichlid native to this country, and among the few...
and Steatocranus
Steatocranus
Steatocranus is a small genus of rheophilic cichlid fish. Most are endemic to the Congo River Basin in DR Congo/Congo Brazzaville, although one species, S. irvinei, is restricted to the Volta River in Ghana....
are also placed herein. They are nowadays placed in the subfamily Pseudocrenilabrinae
Pseudocrenilabrinae
The Pseudocrenilabrinae is a subfamily in the cichlid family of fishes to which, according to a study from 2004, includes all the Middle Eastern and African cichlids with the exception of the unusual Heterochromis multidens and the Malagasy species. Previous authors recognized additional African...
of Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
n and Middle East
Middle East
The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...
ern cichlids; formerly these were often regarded as a distinct subfamily Tilapiinae.
Systematics
The tilapiines were recognised by the ichthyologistIchthyology
Ichthyology is the branch of zoology devoted to the study of fish. This includes skeletal fish , cartilaginous fish , and jawless fish...
Ethylwynn Trewavas
Ethylwynn Trewavas
Dr. Ethelwynn Trewavas was an ichthyologist at the British Museum of Natural History. She was known for her work on the families Cichlidae and Sciaenidae...
. http://www.safarilands.org/index.php/wildlife/more/frequently_asked_questions_on_tilapiine_cichlids/
Recent DNA sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
analyses, however, suggest that the Tilapiini as presently delimited are not monophyletic. mtDNA studies found that Tilapia, in which formerly all tilapias were united, still seemes to constitute a paraphyletic assemblage, composed of a basal grade, T. bemini
Tilapia bemini
Tilapia bemini is a critically endangered species of fish in the cichlid family. It is endemic to Lake Bermin in Cameroon. It is threatened by pollution and sedimentation from human activities, and potentially also by large emissions of carbon dioxide from the lake's bottom .-Source:* World...
which seems closer to haplochromines, and a group containing for example T. buttikoferi
Tilapia buttikoferi
Tilapia buttikoferi are a large African tilapiine cichlid fish that can be found mainly in West Africa, specifically Liberia. They are freshwater fish that tend to live in rivers and streams...
and T. ruweti of presently unresolved relationships. The first group as well as Iranocichla
Iranocichla
Iranocichla hormuzensis is a species of mouthbrooding fish from the cichlid family. It is the only member of its genus, and reaches a length of about . It is restricted to freshwater and brackish habitats in southern Iran. It is the only species of cichlid native to this country, and among the few...
, Oreochromis
Oreochromis
Oreochromis is a large genus of tilapiine cichlids, fishes endemic to Africa and the Middle East. Several species from this genus have been introduced far outside their native range, and are important in aquaculture...
, Sarotherodon
Sarotherodon
Sarotherodon is a genus of tilapiine cichlids, fishes endemic to Africa and the Middle East. A few species from this genus have been introduced far outside their native range, and are important in aquaculture. They mainly inhabit fresh and brackish water, but a few can live in salt water...
and Tristramella
Tristramella
Tristramella is a genus of fishes in the Cichlidae family. The four species in this genus are restricted to Israel and Syria, where they are among the relatively few native cichlids .Tristramella intermedia and T...
are fairly close to tribes such as the Lamprologini
Lamprologini
Lamprologini is a tribe of African cichlid fishes. It contains seven genera and nearly 100 species. Over half of the species in this tribe are in the large genus Neolamprologus. Most genera in the tribe are endemic to Lake Tanganyika, but one species of Neolamprologus Lamprologini is a tribe of...
and Tropheini
Tropheini
Tropheini is a tribe of African cichlids, endemic to Lake Tanganyika.-Genera:*Limnotilapia*Lobochilotes*Simochromis*Petrochromis*Pseudosimochromis*Tropheus-External links:...
. Unfortunately, the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the 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 might also do so between the lineages. Gene pool
Gene pool
In population genetics, a gene pool is the complete set of unique alleles in a species or population.- Description :A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection...
s 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
Pseudocrenilabrinae
The Pseudocrenilabrinae is a subfamily in the cichlid family of fishes to which, according to a study from 2004, includes all the Middle Eastern and African cichlids with the exception of the unusual Heterochromis multidens and the Malagasy species. Previous authors recognized additional African...
(African cichlids).
A small sample size
Sample size
Sample size determination is the act of choosing the number of observations to include in a statistical sample. The sample size is an important feature of any empirical study in which the goal is to make inferences about a population from a sample...
—one to a mere handful of specimens per taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
—as is often used in molecular studies further acerbates the problem. As discussed below for the example of mouthbreeding
Mouthbrooder
Mouthbrooding, also known as oral incubation and buccal incubation, is the care given by some groups of animals to their offspring by holding them in the mouth of the parent for extended periods of time. Although mouthbrooding is performed by a variety of different animals, most notably Darwin's...
, non-molecular data such as morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
or behavior
Behavior
Behavior or behaviour refers to the actions and mannerisms made by organisms, systems, or artificial entities in conjunction with its environment, which includes the other systems or organisms around as well as the physical environment...
has also turned out to be extremely prone to homoplasies, not the least due to the small but ongoing gene flow
Gene flow
In population genetics, gene flow is the transfer of alleles of genes from one population to another.Migration into or out of a population may be responsible for a marked change in allele frequencies...
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. 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
Oreochromis
Oreochromis is a large genus of tilapiine cichlids, fishes endemic to Africa and the Middle East. Several species from this genus have been introduced far outside their native range, and are important in aquaculture...
and Sarotherodon
Sarotherodon
Sarotherodon is a genus of tilapiine cichlids, fishes endemic to Africa and the Middle East. A few species from this genus have been introduced far outside their native range, and are important in aquaculture. They mainly inhabit fresh and brackish water, but a few can live in salt water...
are mouthbrooder
Mouthbrooder
Mouthbrooding, also known as oral incubation and buccal incubation, is the care given by some groups of animals to their offspring by holding them in the mouth of the parent for extended periods of time. Although mouthbrooding is performed by a variety of different animals, most notably Darwin's...
s, 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
Lek (animal behaviour)
A lek is a gathering of males, of certain animal species, for the purposes of competitive mating display. Leks assemble before and during the breeding season, on a daily basis. The same group of males meet at a traditional place and take up the same individual positions on an arena, each occupying...
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. 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.