Snowflake reproduction 2:The snowflakes reproduce by spitting out "propagules" once they reach a large size. Once the propagule has grown (through a series of cell divisions) to be large enough, it too spits out a new propagule.The actual paper is very accessibly written and totally understandable by the average non-creationist:
Snowflake settling: The multicellular yeast clusters look like "snowflakes" as they settle to the bottom of their container.
Snowflake genetic stability: Single cells of snowflake-phenotype yeast regenerate new snowflake-phenotype clusters.
Snowflake size evolution: Time-lapse microscopy of derived rapid settling (left) and slow settling (right) genotypes isolated from 5 minute and 25 minute settling regimes, respectively. Cultures were grown for 24 h, diluted 300-fold, and grown in 0.5 uL YPD. Time-lapse microscopy was performed with images taken every minute for 600 minutes.
Experimental evolution of multicellularity (PDF)
Multicellularity was one of the most significant innovations in the history of life, but its initial evolution remains poorly understood. Using experimental evolution, we show that key steps in this transition could have occurred quickly. We subjected the unicellular yeast Saccharomyces cerevisiae to an environment in which we expected multicellularity to be adaptive. We observed the rapid evolution of clustering genotypes that display a novel multicellular life history characterized by reproduction via multicellular propagules, a juvenile phase, and determinate growth. The multicellular clusters are uniclonal, minimizing within-cluster genetic conflicts of interest. Simple among-cell division of labor rapidly evolved. Early multicellular strains were composed of physiologically similar cells, but these subsequently evolved higher rates of programmed cell death (apoptosis), an adaptation that increases propagule production. These results show that key aspects of multicellular complexity, a subject of central importance to biology, can readily evolve from unicellular eukaryotes..
This suggests that the evolutionary leap to multicellularity may be a surprisingly small hurdle.It suggests that formerly multicellular organisms don't completely lose that ability.
"Our yeast are not utilizing ‘latent’ multicellular genes and reverting back to their wild state. The initial evolution of snowflake yeast is the result of mutations that break the normal mitotic reproductive process, preventing daughter cells from being released as they normally would when division is complete. Again, we know from knockout libraries that this phenotype can be a consequence of many different mutations. This is a loss of function, not a gain of function. You could probably evolve a similar phenotype in nearly any microbe (other than bacteria, binary fission is a fundamentally different process). We find that it is actually much harder to go back to unicellularity once snowflake yeast have evolved, because there are many more ways to break something via mutation than fix it. The amazing thing we see is that we rapidly see adaptations to this adaptation. If we select for more rapid settling, snowflake yeast evolve to delay reproduction until the parent is larger, allowing it settle more quickly. We see the evolution of higher rates of apoptosis as a way to regulate the size and number of propagules produced. We show that the transition to multicellularity in yeast is surprisingly easy, and have no reason to suspect it would be any harder in other microbes with a reproductive process similar to yeast."posted by Blasdelb at 2:31 PM on November 9, 2012 [1 favorite]
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Also, not everyone is super stoked, the response and comments are particularly interesting.
posted by Blasdelb at 12:02 PM on November 9, 2012 [1 favorite]