Algae held captive and genes stolen in crime of evolution

Nov 28, 2012
Electron micrograph of Bigelowiella natans. Credit: Paul Gilson

Microscopic animals held algae captive and stole their genes for energy production, thereby evolving into a new and more powerful species many millions of years ago reveals a new study published today in the journal Nature.

The results reveal a 'missing link' in evolution because the tiny animal thieves () couldn't completely hide all evidence of the captive algae, and have been effectively frozen in time and caught in the act by genetic sequencing.

The protozoa captured for photosynthesis- the process of harnessing light to produce energy which is used by all plants and algae on earth - so the study also provides insight into the origin and repurposing of these genes and may be useful in algae biofuel production.

The work was conducted by an international team of researchers led by Dalhousie University in Canada and included Professor Geoff McFadden from the University of Melbourne.

Professor McFadden from the School of Botany said that scientists had long suspected that quantum leaps of evolution occurred by one organism cannibalizing another, but we did not have much hard evidence.

But when they looked at two specific algae- Guillardia theta and Bigelowiella natans- the team realized the evolution was not quite complete. They could see that their cells had two (like the control centre of the cell that contains DNA). This is unusual because plant and animal cells only have one, so the genes were sequenced to find out more.

"We think that the genes for photosynthesis originally evolved only once about three billion years ago. So all plants, algae and blue green bacteria can produce their own energy from light because they have acquired these genes for photosynthesis," Professor McFadden said.

Like prisoners in Alcatraz, the captive appear to have been nurtured by their enslavers and the precious sugars produced from photosynthesis became a vital part of the protozoan slave keeper's diet. The captives lived inside the protozoan cell and, under the right conditions, the pair gradually became unified as a single organism- a process called endosymbiosis, literally living inside each other.

"We discovered that the captors were initially able to keep many separate clones of their slaves and occasionally pillage one or two for most of the essential genes. However, at some point in time, the number of captives reduced inside each gaoler to just one individual.

"So if they broke into the alga's cell to steal the last essential genes, they would destroy it in the process and would not then be able to use the genes to run . So the two cells, one captive and one captor, had apparently reached an evolutionary stand-off situation where both are dependent on each other to survive."

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Argiod
1 / 5 (2) Nov 28, 2012
So, essentially this is a symbiotic relationship, not parasitic; as both benefit from the relationship...
JVK
1 / 5 (3) Nov 29, 2012
"...reproduction began with an active nutrient uptake mechanism in heterospecifics and the mechanism evolved to become symbiogenesis in the conspecifics of asexual organisms. In yeasts, epigenetic changes driven by nutrition might then have led to the creation of novel cell types, which are required at evolutionary advent of sexual reproduction. These epigenetic changes probably occur across the evolutionary continuum that includes both nutrition-dependent reproduction in unicellular organisms and sexual reproduction in mammals. For example, ingested plant microRNAs influence gene expression across kingdoms. In mammals, this epigenetically links what mammals eat to changes in gene expression and to new genes required for the evolutionary development of the mammalian placenta and the human brain. Cited works included: see http://dx.doi.org...i0.17338 As an alternative, it could be random mutations that drive adaptive evolution. Is there a model for that?