Monisoluisuuden evoluutio

Monet palstalaiset varmastikin muistavat William Ratcliffin ja Michael Travisanon tutkimuksen parin vuoden takaa, jossa käsiteltiin monisoluisuuden evoluutiota. Tutkimuksessa havaittiin, että monisoluisuus ja tehtävänjako solujen välillä voi kehittyä nopeasti ilman suuria geneettisiä muutoksia. Tutkimuksessa he käyttivät Saccharomyces cerevisiae nimistä yksisoluista hiivaa.

Michael Behe teki tälle tutkimukselle surullisen kuuluisan vastineen ( suom. http://www.intelligentdesign.fi/2012/01/26/darvinistista-rappeutumista-paljon-melua-hiivasta/ ) , jossa hän vahingossa väitti, ettei monisoluisuuden syntyminen edes mikään ongelma ollutkaan. Muutenkin vastine oli lähinnä tutkimuksen tulosten vähättelyä ja vääristelyä sanakikkailulla.

No sitten itse asiaan. Nyt William Ratcliff ja Michael Travisano ovat menneet tutkimuksissaan eteenpäin ja selvittäneet jälleen yhden palasen tuosta palapelistä, kuinka monisoluisuus tarkalleen ottaen syntyi. Ei ole nyt hirveästi aikaa, joten lainaan lähinnä suoraan uutisesta.

"Until now, biologists have assumed that this single-cell bottleneck evolved well after multicellularity, as a mechanism to reduce conflicts of interest among the cells making up the organism," says Ratcliff. "Instead, we found that it arose at the same time as multicellularity. This has big implications for how multicellular complexity might arise in nature, because it shows that this key trait, which opens the door to evolving greater multicellular complexity, can evolve rapidly."

In an article published today in the journal Nature Communications, the researchers described how they produced the multi-celled strain by repeatedly selecting and culturing algae that settled quickly to the bottom of a liquid-filled test tube. After 73 rounds, they discovered that the algae in one of the tubes had gone multicellular.

Observing the new form, Ratcliff and Travisano discovered that it reproduced by actively breaking up, shedding motile single cells that go on to grow into new multicellular clusters. They developed a mathematical model that explained the reproductive benefit of this single-celled strategy over hypothetical alternatives in which the cluster would produce larger propagules. The model predicted that reproduction from single cells would be more successful in the long run. Even though single cells are less likely to survive than larger propagules, this disadvantage is more than made up for by their sheer number.

In collaboration with Matthew Herron and Frank Rosenzweig at the University of Montana, the researchers are now working to find the genetic basis for multicellularity and experimentally evolve even greater multicellular complexity.

"Understanding the origins of biological complexity is one of the biggest challenges in science," Travisano said. "In this experiment we've reordered one of the first steps in the origin of multicellularity, showing that two key evolutionary steps can occur far faster than previously anticipated. Looking forward, we hope to directly investigate the origins of developmental complexity, or how juveniles become adults, using the multicellular organisms that we evolved in the lab."

http://phys.org/news/2013-11-scientists-major-piece-biological-complexity.html

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