Given the success of cichlids, understanding the evolution of these two jaws has become an important line of inquiry for biologists. “We’re trying to gain a better understanding of the origins and maintenance of biodiversity,” says Albertson. Researchers have long thought that the two sets of jaws are evolutionarily decoupled and can evolve independently of one another, pushing the boundaries of morphological evolution. However, Conith and Albertson demonstrated that such decoupling does not appear to be the case for cichlids, challenging a quarter-century-old assumption. “What we’ve found is not just that the evolution of the two sets of jaws is linked, but that they’re linked across multiple levels, from genetic to evolutionary,” says Albertson
These findings are a significant step forward in better understanding how evolution works. For instance, many models of evolution theorize both that organisms are constructed from repeated units — digits on your hand or teeth in your mouth — and that these individual units evolve independently from one another. “It is this ‘modularity’ of organisms that is thought to facilitate the evolutionary process,” Albertson notes.
Linked systems are usually thought to lack evolutionary potential. “They just cannot evolve in as many dimensions,” Conith says. This is referred to as an evolutionary constraint, and it plays an important role in shaping biodiversity. Constraints determine what body structures are possible.
Remarkably, this constraint seems to be the key to cichlid’s success by promoting rapid shifts in jaw shapes and feeding ecology, all of which is likely to be an advantage in a dynamic and fluctuating environment, like the East African Rift Valley, where Lake Malawi is located. “The constraint is actually facilitating cichlid evolution, rather than impeding it,” says Conith.
“This tells us that we need to rethink the fundamentals of evolutionary mechanisms,” says Albertson. “Perhaps constraints play a wider role in the evolutionary success of species around the world.”University of Massachusetts Amherst, “Jaws; or, how an African ray-finned fish is helping to rethink the fundamentals of evolution” at ScienceDaily
Another Principle of evolution out the window… constraints can be advantages after all.
The paper is open access.