Through evolution, communities of living organisms adapt to their environment. Organisms that are well-suited to their environment survive and reproduce, passing along their traits. Those ill-suited to the environment die out. An accelerated version of this is called adaptive radiation. In adaptive radiation a species moves into a new and isolated habitat. Because the new habitat provides a variety of new places to live, things to eat, and potential dangers, this original species can rapidly evolve new and varied traits – thus creating the opportunity for new species which each make use of a different niche in the new habitat.

Recently, a group of researchers looked at cichlids, a variety of fish that includes tilapia, in two lakes in Africa: Lakes Mweru and Bangweulu. Both of these lakes have cichlid populations, are deep, and are located in a geographic location where adaptive radiations are known to occur. Lake Bangweulu is relatively isolated by rivers that are hard for fish to travel up, but Lake Mweru has had some fish travel from Lake Bangweulu to Lake Mweru and join the existing population of fish.

The researchers studied the type of fish in each lake. In Lake Bangwelu, they found only a handful of cichlid species—all of them previously identified by different scientists. In Lake Mweru, however, they found many more species of cichlid, including 40 species they believe to have been previously undiscovered. By analyzing the genetic code and the physical appearance of the captured fish, the researchers determined many of the fish in Lake Mweru were related to each other and that they had gone through several adaptive radiations. No adaptive radiation events were found in Lake Bangweulu.

In addition to the discovery of new species, this finding has increased our understanding of how adaptive radiation works. In order for this rapid evolution to occur, species who move into a new habitat must be relatively isolated. If they are instead joined by many species from their previous habitat, there are fewer new roles for them to assume in the new habitat. However, closely related animals can take up roles in an ecosystem, preventing the original species from evolving to fill those roles, which would prevent an adaptive radiation event. On the other hand, closely related lineages in a new ecosystem can interbreed and produce offspring with new traits that can fill the new ecological roles, which could cause an adaptive radiation to occur. This study showed that, in the cichlid population in Lake Mweru, these hybridized offspring can carry traits that lead to adaptive radiation.

Corresponding Author: Emily Kerr

Original Scientific Article: The coincidence of ecological opportunity with hybridization explains rapid adaptive radiation in Lake Mweru cichlid fishes

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Image Credit: https://commons.wikimedia.org/wiki/File:Baby_firemouth_cichlid.jpg