It sounds like a scene out of a science-fiction movie – microscopic animals that captured algae, held them captive and stole their genes for energy production, thereby evolving into a new and more powerful species.
But that is what scientists are saying happened many million years ago, in a new study published in the journal Nature.
Scientists have long suspected that quantum leaps in evolution occurred by one organism cannibalising each other but did not have much hard evidence, said Professor Geoff McFadden (School of Botany, The University of Melbourne), who is part of the international research team led by Dalhousie University in Canada.
In this instance, these microscopic animals (protozoa) used the stolen genes for photosynthesis, the process of harnessing light to produce energy and one that is used by all plants and algae on earth.
In the study, researchers sequenced the genes of two specific algae, Guillardia theta and Bigelowiella natans, after realising that their evolution was not complete – the algae cells had two nuclei (the control centre of the cell that contains DNA), which is unusual because plant and animal cells only have one nucleus.
The results reveal a “missing link” in evolution, as the protozoa couldn’t completely hide all evidence of the captive algae, having been frozen in time and thus “caught in the act” by the genetic sequencing.
“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 obtained these genes for photosynthesis,” Prof McFadden said.
The captive algae appear to have been nurtured by their enslavers, and the precious sugars produced by 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 a single, unified 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 photosynthesis. 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.” Prof McFadden said.
The study also sheds some light into the origin and repurposing of these genes, which may be useful in algae biofuel production.