Claim: Hybridization “boosts evolution” in cichlids
|August 14, 2018||Posted by News under Evolution, speciation|
Animals that have either migrated to or been introduced in Central Europe — such as the Asian bush mosquito or the Asian ladybeetle — feel extremely comfortable in their new homes due to changing climatic conditions. If these newcomers are genetically compatible with local species, they may crossbreed and produce hybrids, which can continue to evolve under local environmental conditions — a process that has been shown to have taken place during human evolution, between Homo sapiens and Neanderthals for example. New genes contributed by foreign species provide new genetic combinations that can be beneficial and are thus favoured by natural selection. According to hybrid swarm theory, interbreeding between hybrid species and parent species may then lead to divergent populations and even to new species with novel characteristics.
What does “boosts evolution” mean, exactly? Does “lead to new species” mean“irreversible changes that prevent breeding back into the parent population or into other descendant populations?” Do these changes amount to a significant amount of new information that enables the new species to survive and pass on genes where otherwise it would not? Something like that could be an example of “boosting evolution.”
By collecting cichlid fish DNA and then sequencing more than 500 selected fish genes via cutting-edge genomic sequencing techniques, the research team was able to establish new evolutionary trees for the East African cichlids and explain why new species sometimes appear in bursts. The researchers found that even at the beginning of the oldest cichlid radiation, environment-induced hybridization between the colonizer lineages produced innovative forms, which then expanded rapidly under stable conditions, thus “boosting” the speed of innovation and species development. In regard to the evolutionary development of ‘modern’ cichlids from Lake Tanganyika and in accordance with the hybrid swarm theory, the research team discovered that a cichlid species from the Lower Congo River reached the lake and interbreed with their lake ancestors, thereby facilitating the adaptive radiation of the cichlids in Lake Tanganyika. This river cichlid is no longer physically present in today’s lake but could be detected via genetic information in the other diversifying lineages.
Some cichlid genes — such as those influencing body colouration and specialisation of the jaw — diversified more rapidly and are associated with the colonisation of new lake environments. “It is those characteristics that are exposed to selection that are responsible for the development of new species,” explains Christian Sturmbauer. Using the latest anchored hybrid sequencing methodology, the research team was able to show for the first time that the jaw innovations of cichlids are crucial in terms of providing the fish access to previously unexploited food sources.
The article here does not say whether these changes are irreversible, as opposed to merely characteristics that might be displayed temporarily by groups of hybrids. How was it decided that they were “species” anyway?
We do learn something of considerable interest thought:
The research team around Axel Meyer and Christian Sturmbauer were also able to shed light into the much-discussed chronology of events (timetree) relating to cichlid evolution: up until now, studies that used molecular clock calibrations resulted in ages that were either too young or too old, and which were generally problematic to reconcile with the geological history East Africa. Using a set of fossil calibrations that includes a newly discovered fossil anchoring the Tanganyikan radiation, the research team carried out a new molecular clock analysis that for the first time reconciles the split of the southern Gondwana continent with the chronology of the sinking of the East African Rift Valley where Lake Tanganyika cichlids evolved together with the maturing lake ecosystem. “These findings may help us understand, for example, ongoing changes induced by climate change in the animal kingdom,” emphasises Sturmbauer. [emphasis added] Paper. (open access) – Iker Irisarri, Pooja Singh, Stephan Koblmüller, Julián Torres-Dowdall, Frederico Henning, Paolo Franchini, Christoph Fischer, Alan R. Lemmon, Emily Moriarty Lemmon, Gerhard G. Thallinger, Christian Sturmbauer, Axel Meyer. Phylogenomics uncovers early hybridization and adaptive loci shaping the radiation of Lake Tanganyika cichlid fishes. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-05479-9 More.
“up until now, studies that used molecular clock calibrations resulted in ages that were either too young or too old, and which were generally problematic to reconcile with the geological history East Africa.”? So the molecular clock is not the Big Answer Machine it is often portrayed to be. And we are still looking for the Darwin machine that produces vast amounts of complex, new information from random events.
A similar situation involves Darwin’s Finches, a longtime textbook icon where the famed speciation appears mainly to be a drift back and forth, depending on the environment the finches encounter. Yes natural selection is at work but because the selecting conditions keep changing, it does not seem to lead anywhere in particular.
See also: Epigenetics may explain how Darwin’s finches respond to environment
So the textbook Darwin’s finches, revered icons of textbook evolution, are not a good example? Never mind. They’ll still be in the books a decade from now anyway. As Zombie Science shows, these icons just keep coming back.
Darwin’s finches not a good example of Darwinian evolution, but of hybridization
Apparently, hybridization of cichlids is a regular source of controversy among aquarists: