Evolution of Multicellular Lineages: A Study of Snowflake Yeast

Tuesday - May 16 2023, 06:19 UTC - 1 year ago

This study investigates the transition from single cell organisms to robust multicellular organisms by researching snowflake yeast. After generations of lab evolution, the snowflake yeast adapted to become physically stronger and larger, providing insights into the biophysical limitations of size and toughness of multicellular life. This is the first major report of the ongoing MuLTEE experiment, which the team hopes to run for decades.

This work is to give a better understanding of the transition from single cell organisms to robust multicell organisms. Precisely how multicellular organisms evolved from single-celled ancestors remains poorly understood. The transition happened hundreds of millions of years ago, and early multicellular species are largely lost to extinction.

Researchers initiated the first long-term evolution experiment aimed at evolving new kinds of multicellular organisms from single-celled ancestors in the lab. Over 3,000 generations of laboratory evolution, the researchers watched as their model organism, "snowflake yeast," began to adapt as multicellular individuals.

In research published in Nature, the team shows how snowflake yeast evolved to be physically stronger and more than 20,000 times larger than their ancestor. This type of biophysical evolution is a pre-requisite for the kind of large multicellular life that can be seen with the naked eye. Their study is the first major report on the ongoing Multicellularity Long-Term Evolution Experiment (MuLTEE), which the team hopes to run for decades.

"Conceptually, what we want to understand is how simple groups of cells evolve into organisms, with specialization, coordinated growth, emergent multicellular behaviors, and life cycles – the stuff that differentiates a pile of pond scum from an organism that is capable of sustained evolution," Ratcliff said. "Understanding that process is a major goal of our field." .

Observations from MuLTEE revealed that over 600 generations the snowflake yeast evolved to a substantially larger size and toughness, and an entirely new lifestyle. In the mixotrophic treatment group, the micro-organisms evolved to become significantly larger, growing up to 2 millimetres. This was an enormous growth, equalling an increase of over 20,000 fold in size compared to their entirely single-celled ancestors.

The snowflake yeast also provided insight into how cells overcome the biophysical limitations of size and toughness. The evolutionary transition to multicellularity enabled snowflake yeast to survive more extreme environmental conditions, such as hypoxia-driven metabolic stress. The researchers observed the micro-organisms to form complex structures, such as spine like structures, with fine cellular details. The intercellular interactions between the snowflake yeast cells is required for the groups to stay together and expand in size.

Snowflake yeast has the distinction of being the first lineage to ever be selected for multicellular traits in a long-term evolutionary experiment. It provides researchers a unique opportunity to study how huge increases in size and toughness can be achieved from simple multicellular life forms. The study demonstrates the potential for such long-term experiments to uncover insights into the evolution of multicellular complexity in animals.