A giant, trumpet-shaped cell that skulks in the bottom of ponds has given scientists a new clue about how single-celled creatures may have taken the first steps towards evolving into multicellular ones, a key transition in the evolution of life.
For this to happen, there had to be a benefit for single cells to club together, such as improved reproduction or feeding. Studies investigating these ideas have focused mainly on creatures that form groups or colonies in which some cells develop specialised functions, and where they remain glued together for some or all of the time. Biologists think they may represent a stage of evolution that is partway down the path to multicellularity.
at Emory University in Atlanta, Georgia, and his colleagues have spotted a simpler, reversible form of multicellular behaviour in Stentor coeruleus, a single-celled protist that can grow up to 2 millimetres long.
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Shekhar was studying Stentor in a lab dish when he noticed that individual cells use a fringe of whip-like cilia around their 鈥渉eads鈥� to generate pairs of vortices to suck food into their 鈥渕ouths鈥�. Furthermore, while some cells were freely swimming around, others stuck to the dish and formed colonies. He wondered whether this helped Stentor trap more food.
To find out more, Shekhar and his team put pairs of Stentor cells in a fluid-filled chamber. The cells put their heads together and their vortices combined, creating a much stronger flow that could draw in more and bigger prey. 鈥淚t almost appears like a single, big Stentor instead of two small Stentor,鈥� says Shekhar.
If this is so advantageous, why don鈥檛 Stentor cells stick together all the time? Shekhar thinks it is because the benefit is unequal, with the stronger cell getting a better deal than the weaker one. So Stentor cells in colonies waggle their heads between each of their neighbours, swapping partners all the time to maximise their fluid flow.
鈥淏y giving up a little bit of their independence, they are benefiting as a whole, as a colony,鈥� says Shekhar. While the colonies remain roughly constant in size, each Stentor comes and goes, like a guest at an open house party.
The findings describe a form of simple multicellularity that is driven by a fast and reversible cellular behaviour, rather than a programmed and irreversible developmental process, says at the Pasteur Institute in Paris. 鈥淭his provides an unusual and elegant possible route for the early evolution of multicellularity that had not been quite on the radar before.鈥�
Reference: bioRxiv,
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