African cichlids are fish from the Tsikhlov family that live in the Great African Lakes . The most studied fish from lakes Victoria , Malawi and Tanganyika . Total in
Great African lakes, there are 1,500 species of cichlids, occupying all ecological niches available to fish. All of them have a common ancestor, and their divergence occurred quite quickly (over 10 million years). Only in Lake Victoria, 200 species of these fish live. This diversity seems surprising when you consider that the lake itself is about 400,000 years old and that speciation usually requires long-term isolation of some populations from others, and in the lakes this is almost impossible. Lake Malawi is located at an altitude of 474 meters above sea level, with an area of almost 31,000 km², it flows through the territory of three African countries. The lake is home to 500 species of cichlids. The cichlids of this lake are divided into two groups mbuna and utaka and differ in morphological characteristics and food addiction. Many African cichlids incubate caviar in the mouth .
Content
History
British paleontologists found that cichlids occupied their modern habitats much later than Gondwana split into Africa, South America, India and Australia. This means that at some point in their history, these freshwater fish had to cross the salty seas. The study was published in the journal Proceedings of the Royal Society B, and ScienceNow writes briefly about it.
The authors' conclusions are based on two lines of argumentation. First, scientists systematized all existing paleontological finds of the ancestors of cichlids and compared them with how often it is possible to detect fossils of other fish. The oldest prints of cichlids date back 45 million years ago. If such fish existed even before the separation of Gondwana (135 million years ago), their absence in the fossil record could be explained only by a sharp drop in the probability of detection by 10-30 times.
Second, scientists sequenced 10 cichlid-specific genes from their 89 modern descendants. Comparison of sequences allowed us to establish the time of the divergence of the group at 57-65 million years ago, which is half the time elapsed since the collapse of Gondwana.
According to the researchers, this suggests that the most popular hypothesis of the distribution of cichlids is most likely not true. This hypothesis claims that the ancestors of animals fell passively on different continents of the southern hemisphere - as a result of the collapse of Gondwana. If this is not the case, then the ancestors of the cichlids had to travel considerable distances through the salty waters before getting into their current habitats. All cichlids are freshwater fish, but this exotic hypothesis may be supported by the fact that some of them, such as tilapia, can withstand brackish water.
Cichlids are a model object for many evolutionary studies. Recently, it was shown on them that the separation of ecological niches is not necessary for the formation of new species. Sometimes species formation can be explained by the appearance of different subjective preferences in different females.
Morphology
Literature
- John Reader Africa. Washington, DC: National Geographic Society, 2001. P. 227
- Douglas J. Futuyma. Evolutionary Biology. Sunderland, MA: Sinauer Associates, 1998.
- Mark Ridley Evolution. Boston: Blackwell Scientific, 1993.