Normal 0 false false false MicrosoftInternetExplorer4 Some cichlid fish see red better while others only have eyes for blue. This difference in vision, observed in fish in an African lake, could be pushing red-bodied cichlids to branch off from their blue-bodied brethren and to form a new species.
If so, it would be the first time that scientists have caught evolution in the act of creating a new species because of changes in sense organs. For one species to diverge into two, some barrier must prevent two groups of individuals from interbreeding. Physical separation of two groups and changes to reproductive organs are two of the wedges that scientists have shown can drive the formation of new species, and evolutionary biologists are always keen to discover new mechanisms.
“Speciation can occur even without physical isolation when individuals are adapted to a particular environment by [their] sensory system,” says Norihiro Okada, an evolutionary biologist at Tokyo Institute of Technology.
Okada and his colleagues had previously shown that cichlid fish in Lake Victoria’s shallow waters are bathed in bluer light, while the turbid water of the lake predominantly lets redder light filter down to fish living in deeper water. The researchers showed that the fish’s eyes have adapted to this difference so that fish that live in deeper water have a pigment in their eyes that is more sensitive to red light, while shallow-water fish have a pigment that’s sensitive to blue.