The Paths to Multicellularity Are Many



Here on earth, life has evolved multicellularity dozens of times since the first proto-biological forms took shape (at least 25 times according to Grosberg and Strahmann). There is however no need to teleport to the past as we can now observe directly this metamorphosis by dint of experiment.

In the past month two separate trials with single-celled yeast have shown how yeast respond in the face of different selection pressures. Instead of separating from the mother cell into two distinct daughter cells (mitosis), or untethering itself from the parent cell after maturity (budding), new yeast cells globbed together in both of the experiments, creating an amorphous blob geared to outcompete its neighbors. That is, the transition from unicellularity to multicellularity has now been observed and monitored in the lab.

“To investigate these clumps, the Harvard scientists put them in a flask with their single-celled ancestors and let them compete for the sucrose. Every time the researchers ran the experiment, the multicellular clumps won, swiftly eliminating their ancestors. Their victory strongly suggests that natural selection was responsible for their evolution to clumps.

This increase in mass provides various functional benefits, such as conforming to a sucrose-based diet in the case of the trial at Harvard.

The scientists then took a close look at the biochemistry of the evolved yeast. They gained an advantage partly from an improvement in how they fed. The evolved yeast produced more sucrose-digesting enzymes. They also made more proteins to transport the smaller sugars into their interior.”

This latest experiment at Harvard (and various others like it) illustrates elegantly the degree to which biology is shaped by its environment. Changing up food sources or food scarcity can dramatically reshape populations as natural selection determines which individuals are better suited to the latest pressures operating in their habitat. This bottom-up process of “design by adaptation” is a one of great ingenuity and flexibility.

So in the space of a month, we have two studies that see the origin of multicellularity in the same species–but for two separate reasons.


External link: Another Path For Evolving Bodies

Feature image courtesy of Wikimedia Commons