+M2Ys4U Subscriber¹ Posted June 23, 2011 Subscriber¹ Share Posted June 23, 2011 IN JUST a few weeks single-celled yeast have evolved into a multicellular organism, complete with division of labour between cells. This suggests that the evolutionary leap to multicellularity may be a surprisingly small hurdle.Multicellularity has evolved at least 20 times since life began, but the last time was about 200 million years ago, leaving few clues to the precise sequence of events. To understand the process better, William Ratcliff and colleagues at the University of Minnesota in St Paul set out to evolve multicellularity in a common unicellular lab organism, brewer's yeast. Their approach was simple: they grew the yeast in a liquid and once each day gently centrifuged each culture, inoculating the next batch with the yeast that settled out on the bottom of each tube. Just as large sand particles settle faster than tiny silt, groups of cells settle faster than single ones, so the team effectively selected for yeast that clumped together. Sure enough, within 60 days - about 350 generations - every one of their 10 culture lines had evolved a clumped, "snowflake" form. Crucially, the snowflakes formed not from unrelated cells banding together but from cells that remained connected to one another after division, so that all the cells in a snowflake were genetically identical relatives. This relatedness provides the conditions necessary for individual cells to cooperate for the good of the whole snowflake. "The key step in the evolution of multicellularity is a shift in the level of selection from unicells to groups. Once that occurs, you can consider the clumps to be primitive multicellular organisms," says Ratcliff. In some ways, the snowflakes do behave as if they are multicellular. They grow bigger by cell division and when the snowflakes reach a certain size a portion breaks off to form a daughter cell. This "life cycle" is much like the juvenile and adult stages of many multicellular organisms. After a few hundred further generations of selection, the snowflakes also began to show a rudimentary division of labour. As the snowflakes reach their "adult" size, some cells undergo programmed cell death, providing weak points where daughters can break off. This lets the snowflakes make more offspring while leaving the parent large enough to sink quickly to the base of the tube, ensuring its survival. Snowflake lineages exposed to different evolutionary pressures evolved different levels of cell death. Since it is rarely to the advantage of an individual cell to die, this is a clear case of cooperation for the good of the larger organism. This is a key sign that the snowflakes are evolving as a unit, Ratcliff reported last week at a meeting of the Society for the Study of Evolution in Norman, Oklahoma. Other researchers familiar with the work were generally enthusiastic. "It really seemed to me to have the elements of the unfolding in real time of a major transition," says Ben Kerr, an evolutionary biologist at the University of Washington in Seattle. "The fact that it happened so quickly was really exciting." Sceptics, however, point out that many yeast strains naturally form colonies, and that their ancestors were multicellular tens or hundreds of millions of years ago. As a result, they may have retained some evolved mechanisms for cell adhesion and programmed cell death, effectively stacking the deck in favour of Ratcliff's experiment. "I bet that yeast, having once been multicellular, never lost it completely," says Neil Blackstone, an evolutionary biologist at Northern Illinois University in DeKalb. "I don't think if you took something that had never been multicellular you would get it so quickly." Even so, much of evolution proceeds by co-opting existing traits for new uses - and that's exactly what Ratcliff's yeast do. "I wouldn't expect these things to all pop up de novo, but for the cell to have many of the elements already present for other reasons," says Kerr. Ratcliff and his colleagues are planning to address that objection head-on, by doing similar experiments with Chlamydomonas, a single-celled alga that has no multicellular ancestors. They are also continuing their yeast experiments to see whether further division of labour will evolve within the snowflakes. Both approaches offer an unprecedented opportunity to bring experimental rigour to the study of one of the most important leaps in our distant evolutionary past. Source: New Scientist Link to comment Share on other sites More sharing options...
Teebor Posted June 23, 2011 Share Posted June 23, 2011 Next stop Blue Monkeys!! And another thought, if this originally came from Brewers yeast would it make a more complex tasting beer? Link to comment Share on other sites More sharing options...
blade1269 Posted June 23, 2011 Share Posted June 23, 2011 Next stop Blue Monkeys!! And another thought, if this originally came from Brewers yeast would it make a more complex tasting beer? Why do people think were monkeys. Lame!!! Link to comment Share on other sites More sharing options...
Buttus Posted June 23, 2011 Share Posted June 23, 2011 Why do people think were monkeys. Lame!!! what did we evolve from then, yeast? oh, wait.... Link to comment Share on other sites More sharing options...
Teebor Posted June 23, 2011 Share Posted June 23, 2011 Why do people think were monkeys. Lame!!! Erm what?? I just want someone to make a monkey which is Blue. I couldn't give a crap about evolution Link to comment Share on other sites More sharing options...
jakem1 Posted June 23, 2011 Share Posted June 23, 2011 Well done yeast :beer: Link to comment Share on other sites More sharing options...
Solid Knight Posted June 23, 2011 Share Posted June 23, 2011 That yeast is now ungodly. It must be burned at the stake! Link to comment Share on other sites More sharing options...
Udedenkz Posted June 23, 2011 Share Posted June 23, 2011 !!!! In before, "Bible says no" Link to comment Share on other sites More sharing options...
+M2Ys4U Subscriber¹ Posted June 23, 2011 Author Subscriber¹ Share Posted June 23, 2011 Why do people think were monkeys. Lame!!! Both monkeys and apes (i.e. humans) are simians. Actually the classification of simians families is a little odd because it took place before we really knew how we were related. Apes should also be monkeys, but they're not. We are Hominoidea (apes, family Hominidae aka the "great apes": chimpanzees, gorillas, humans, and orangutans) and the classification of monkeys is shown in green. Link to comment Share on other sites More sharing options...
jakem1 Posted June 23, 2011 Share Posted June 23, 2011 !!!! In before, "Bible says no" I think there's a bit in the bible that specifically commands the yeast to go forth and multiply. Either that or it was explaining the importance of basic arithmetic - it's just so hard to know how to interpret scriptures these days. Link to comment Share on other sites More sharing options...
guru Posted June 23, 2011 Share Posted June 23, 2011 meh. how is this "multicellular" Link to comment Share on other sites More sharing options...
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