Study shows evolution does not always mean more diversification

November 27, 2015 by Bob Yirka, report

A young Nile perch. Credit: John Uhrig
(—A small team of researchers with members from the U.S. and Switzerland has found an example of a fish that did not always benefit in the end from an evolutionary change. In their paper published in the journal Science, the team describes their study of cichlid fish species in Lake Victoria and other places, and the changes that led to their downfall in one ecosystem. Geerat Vermeij with the University of California offers a Perspectives piece on the work done by the group in the same journal issue.

The researchers were studying pharyngognathy in spiny —where the jaw changes over time to allow bones in the throat to grind down hard shells for digestion—to discover whether such an evolutionary adaption always works out, because the downside of it is a smaller gape, which means feasting on smaller fish. They noted that most such live in shallow marine environments alongside other species that do not have the grinding capability. The exception was cichlids, which live in tropical freshwater places, such as lakes.

Overall, the researchers found that pharyngognathy generally led to fish that evolved into niches that favored hard-shelled fish faster than did other fish, and that may have contributed to the decline of such fish species in Lake Victoria. The Nile perch, a non-pharyngognathous fish was introduced into the lake back in the 1950s and since that time cichlid numbers have been dropping dramatically. Initially it was assumed that the decline was due to the perch eating or killing the various cichlid species, but now, the researchers have shown that it was most likely due to them being out-competed—they compared the feeding performance of Nile perch against cichlids and discovered that the gape of the perch was double that of the cichlids, and that the cichlids also took much longer to digest prey. Taken together, the physical differences have clearly put the cichlids at a serious disadvantage, allowing the perch to thrive while the have been essentially starving to death. Thus, the specialization that came about due to the evolutionary adaption meant to allow them to eat a broader range of fish, in the end led to far less diversification in at least one closed ecosystem.

Harpagochromis, "orange rock hunter," is a beautiful predatory cichlid now found in low numbers in Lake Victoria, but maintained in captivity thanks to conservation-minded cichlid hobbyists. Credit: Matthew McGee
Harpagochromis, "two stripe white lip," is an undescribed species of Victorian predator cichlid now extinct in the wild. Thanks to a partnership with the Lake Victoria Species Survival Program, we were able to use this species in our study. Credit: Matthew McGee
Nile perch are known to prey on cichlids, but they also outcompeted fish-eating cichlids. Credit: Matthew McGee

Explore further: Hormones may help tiny African fish climb social ladder

More information: M. D. McGee et al. A pharyngeal jaw evolutionary innovation facilitated extinction in Lake Victoria cichlids, Science (2015). DOI: 10.1126/science.aab0800

Evolutionary innovations, traits that give species access to previously unoccupied niches, may promote speciation and adaptive radiation. Here, we show that such innovations can also result in competitive inferiority and extinction. We present evidence that the modified pharyngeal jaws of cichlid fishes and several marine fish lineages, a classic example of evolutionary innovation, are not universally beneficial. A large-scale analysis of dietary evolution across marine fish lineages reveals that the innovation compromises access to energy-rich predator niches. We show that this competitive inferiority shaped the adaptive radiation of cichlids in Lake Tanganyika and played a pivotal and previously unrecognized role in the mass extinction of cichlid fishes in Lake Victoria after Nile perch invasion.

Press release

Related Stories

Fish species in Lake Tana genetically surprisingly similar

October 9, 2015

The different species of barbels in Lake Tana in northern Ethiopia have evolved from a common ancestor. When biologists from Wageningen University first described the fifteen species over twenty years ago, it was not yet ...

Lakes resist the introduction of new fish

November 9, 2015

In her dissertation, Anna Henriksson presents a new method of establishing how freshwater fish can defend themselves against an invasion of a new fish species. The method takes into account that resident species in a lake ...

Color matters in display of fish aggression

October 5, 2015

Biologists have unlocked new insights into the mysterious evolution of colour diversity among fish, and how aggression from other species plays a part in patterns of colour diversity observed in the wild.

Recommended for you

Semimetals are high conductors

March 18, 2019

Researchers in China and at UC Davis have measured high conductivity in very thin layers of niobium arsenide, a type of material called a Weyl semimetal. The material has about three times the conductivity of copper at room ...


Adjust slider to filter visible comments by rank

Display comments: newest first

Nov 27, 2015
This comment has been removed by a moderator.
Shaco LePurp
4.2 / 5 (5) Nov 27, 2015
"Theory of evolution is antipod to diversification. From two species or individals remain one according to its main ideas. It can not create biodoversity as random events can not create ot increse informatiion in one physical system. The evolution is mamonic ideology with which those who have gained political and financial power want to justify their iniquity against those who have no their materialistic capabilities and moral. This is a materialistic criminal ideology which has no higher purpose. Its purpose is boringly banal - minority welfare at the expense of the majority interest."

The mind of an anti-evolutionist at work everyone.
2.3 / 5 (3) Nov 27, 2015
Viko is correct, Shaco is French (and plays children's games).
4 / 5 (4) Nov 28, 2015
Viko is only correct if you're a religious fundamentalist with a hatred of science.
2 / 5 (4) Nov 28, 2015

Try to define order without absolutes.
5 / 5 (1) Nov 28, 2015
So yet again the introduction of an alien species into a closed ecosystem has had serious negative effects. Big surprise. Though the analysis of the specific causes of the decline of the cichlid is interesting.
3 / 5 (2) Nov 28, 2015
You don't have to believe in evolution, so long as you're willing to admit that God screwed up and couldn't make a fish that survived.
3.7 / 5 (3) Nov 28, 2015
Try to define order without absolutes.

Try to use words for something other than barking, hissing, growling, and clawing at dirt.
3.7 / 5 (3) Nov 28, 2015
Considering that 99% of all species that have ever existed are now extinct, I'm not seeing how this is a big revelation.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.