The study of algae in Swedish lakes is providing insights into the development of complex life on Earth.

A research team led by Lund University in Sweden has successfully identified the kind of environmental conditions that promote multicellularity, and say the results give new clues to the amazing paths of evolution. Simply put, a multicellular organism is an individual animal or plant composed of many cells.

The evolution of multicellular life has played a pivotal role in shaping biological diversity. The cooperation between cells within multicellular organisms has enabled eyes, wings and leaves to evolve.

However, until now, surprisingly little has been known about the natural environmental conditions that favour the formation of multicellular groups. The predominant explanation is that being in a group enables species to better cope with environmental challenges – where being in a large group can, for instance, protect cells against being eaten.

The researchers say their results challenge this idea, showing that multicellular groups form not because they are inherently beneficial, but rather as a by-product of single-celled strategies to reduce environmental stress.

"In particular, cells produce a range of substances to protect themselves from the environment and these substances appear to prevent daughter cells from dispersing away from their mother cell," says Charlie Cornwallis, biology researcher at Lund University.

Evolutionary experiment

To understand how and why single-celled organisms evolve to be multicellular, the scientists experimented on green algae. These organisms have some species that are always single-celled, some that are single-celled but become multicellular under certain conditions, and some which are always multicellular, containing thousands of cells.

They could then identify the environmental conditions that promote multicellularity and find out the benefits and costs for organisms. The researchers then combined data with information on the environments that single-celled and multicellular green algae are adapted to across the whole of Sweden.

"I was surprised that there were no benefits or costs to living in multicellular groups," says Cornwallis. "The conditions that individual cells experience can be extremely different when swimming around on their own, to being stuck to other cells and having to coordinate activities.

"Imagine you were physically tied to your family members, I think it would have quite an effect on you."

The study was conducted in Swedish lakes, and it not only provides information on which green algae occur and where and why, it also helps brings understanding to the origins of biological diversity that shape the world around us.

Cornwallis concludes, "The results of this study contribute to our understanding of how complex life on Earth has evolved. They also provide information on how a key group of species – green algae that generate fuel for ecosystems – are able to reproduce and survive under different environmental conditions.

"The next time you walk along the shores of a lake rich in nitrogen just imagine that this fosters the evolution of multicellular life, says Charlie Cornwallis."