Is the outcome of evolution predictable?

If one would rewind the tape of life, would evolution result in the same outcome? The Harvard evolutionary biologist Stephen Jay Gould came up with this famous thought experiment. He suggested that evolution would not repeat itself: the role of random processes in the origin of biodiversity was too important and hence evolution was not predictable. Konstanz evolutionary biologists around Prof. Axel Meyer have now described parallel evolution of two closely related, but geographically isolated populations of cichlid fish in Nicaraguan crater lakes. This repeated outcome of evolution is best interpreted as evidence for similar adaptation to similar Darwinian natural selection pressure – and suggests somewhat deterministic evolutionary trajectories. The findings of the Konstanz study have been published in Nature Communications.

There are only very few circumstances in which one can investigate the repeatability of evolution, because spatially independent environments that are populated by the same species are extremely rare in nature. "The young and completely isolated crater lakes along the Central American Volcanic Arc in Nicaragua provide an ideal setting to study . Several crater lakes house populations of Midas cichlid fish that have developed independently from the ancestral population in the nearby great lakes of Nicaragua. This setting is like a natural experiment", explains Axel Meyer.

In two of these crater lakes, Apoyo and Xiloá, new types of Midas cichlids evolved, independently from each other, in less than 10,000 years. These new species show identical morphological adaptations that are not found in the ancestral population: from the shallow, murky water to the new habitat of the deep, clear water of the crater lakes. "In each of the two crater lakes new species of the Midas cichlid evolved with an elongated body – a phenotype that does not exist in ancestral lakes from which the colonisers of crater lakes came from", explains Meyer. His research team studied the morphological, ecological, population genetic, and phylogenetic patterns of these fish. "We found these cichlids to be strong evidence for parallel evolution that – interestingly – took place via different routes. Our findings show that parallel phenotypes can evolve in similar habitats and due to similar selection pressure, however, not necessarily in parallel evolutionary sequence", explains the evolutionary biologist from Konstanz. This indicates that parallel adaptation to similar environments may lead to the same result by natural selection, yet this evolution can proceed along different evolutionary genetic routes. This is because the equivalent endemic species in these two crater lakes originated in different sequences in both lakes. "Now we are looking for the genes and mutations that are the cause for this parallelism", says Axel Meyer.

"Our study shows that complex parallel phenotypes in similar environments can evolve very rapidly, repeatedly and yet via different evolutionary routes. This is a microevolutionary example of rewinding Gould's tape and resulting in the of two very similar species, albeit by non-parallel evolutionary routes", sums up Axel Meyer.

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More information: Kathryn R. Elmer, Shaohua Fan, Henrik Kusche, Maria Luise Spreitzer, Andreas F. Kautt, Paolo Franchini and Axel Meyer. 2014. "Parallel evolution of Nicaraguan crater lake cichlid fishes via non-parallel routes." Nature Communications, DOI: 10.1038/ncomm6168
Journal information: Nature Communications

Citation: Is the outcome of evolution predictable? (2014, October 28) retrieved 18 August 2019 from https://phys.org/news/2014-10-outcome-evolution.html

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Oct 28, 2014
Isolated cases shouldn't be discarded, but are also not a good indicator of the general case.

Let's take sharks as an example. There are over 300 species of shark, and some of them have very odd and unique physical adaptations: Hammerheads, bull sharks, carpet sharks, lemon sharks, etc. Some are very large, such as Great Whites and Whale Sharks, and some are tiny, like the Cigar shark, yet they all live in the open ocean. Similar habitat, very different features.

Oct 28, 2014
This type of convergent evolution, which is similar to many other examples of animals evolving into similar forms (such as dog-like marsupials; bird-like mammals; insect-like birds) does not falsify Gould's observation.

For instance if the dinosaurs remained viable in large numbers then a human-like dinosaur might have eventually evolved. A human-like bird could evolve even now. Indeed, as humans dominate the world today and so the human population is ever more the environment for numerous species we can expect human-like traits to be strongly selected in the future.

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Oct 28, 2014
If the environment is the same then adaptation to that environment will converge, but when there are multiple species in the same environment then each other species is part of the environment for any given species in that environment and this alone will ensure substantial diversity with numerous possible adaptation paths. Only if an environment is populated by a single species can convergence be reliably predicted
