Survival Of The Fittest: Cichlid Fish Prove That Competition, Breeding Patterns Leads To Speciation

By Shweta Iyer on March 1, 2014 1:20 PM EST

cichlid
A team of scientists prove with cichlid fish that evolutionary theory does indeed work. Among a group of cichlids, differences in living space and size led them to develop into two different species. (Photo: golbenge, CC BY-SA 2.0)

"Survival of the fittest" is an evolutionary theory describing the mechanisms of natural selection - competition plays a key role in the evolution of new species. This fact is well documented in Darwin's theory of evolution and other theoretical studies, however, there has been only a limited amount of empirical evidence to prove this. Researchers from the Bristol School of Biological Sciences in England used population genetics and experimental evidence to demonstrate that competition leads to speciation - the splitting of one species into two distinct species - within the highly diverse cichlid fishes of Lake Tanganyika in East Africa.

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Researchers studied the cichlid fish Telmatochromis temporalis and its evolution to a new species. They found that the fish had two genetically distinct ectomorphs - variations in a species whose appearance is determined by its environment - that show huge variations in body size and the habitat in which they live.

"We found large-sized individuals living along the rocky shoreline of Lake Tanganyika and, in the vicinity of these shores, we found small-sized individuals, roughly half the size of the large ones, that live and breed in accumulations of empty snail shells found on sand," lead researcher Dr. Martin Genner said in a statement.  

The researchers observed that the bigger cichlids competed with the smaller ones and forced them to leave their natural rocky habitats for the neighboring sands. The smaller fish sheltered themselves and their eggs in empty snail shells. "In effect, big and small fish use different habitats; and because of this habitat segregation, fish usually mate with individuals of similar size. There is virtually no genetic exchange between the large- and small-bodied ectomorphs," Genner said in the statement.

Speciation occurs when fractions of individuals get separated from others of the same species due to physical barriers or other reasons. This, in turn, causes them to develop genetic differences over time. In the case of the cichlids, there are no obvious obstacles hindering the movement and interaction between the two groups of fish. But, the unlikeliness of mating between large- and small-bodied fish sets the stage for the evolution of a new species.

"The relevance of our work is that it provides experimental evidence that competition for space drives differential mating in cichlid fish and, in time, leads to the formation of new species," Genner said in the statement. "Nature has its ways - from body size differences to the formation of new species. And clearly, size does matter for Telmatochromis and for fish diversity."

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