More Like this

1. Varied solutions to multicellularity: The biophysical and evolutionary consequences of diverse intercellular bonds

   https://doi.org/10.1063/5.0080845  

   Day, Thomas_C; Márquez-Zacarías, Pedro; Bravo, Pablo; Pokhrel, Aawaz_R; MacGillivray, Kathryn_A; Ratcliff, William_C; Yunker, Peter_J (June 2022, Biophysics Reviews)

   The diversity of multicellular organisms is, in large part, due to the fact that multicellularity has independently evolved many times. Nonetheless, multicellular organisms all share a universal biophysical trait: cells are attached to each other. All mechanisms of cellular attachment belong to one of two broad classes; intercellular bonds are either reformable or they are not. Both classes of multicellular assembly are common in nature, having independently evolved dozens of times. In this review, we detail these varied mechanisms as they exist in multicellular organisms. We also discuss the evolutionary implications of different intercellular attachment mechanisms on nascent multicellular organisms. The type of intercellular bond present during early steps in the transition to multicellularity constrains future evolutionary and biophysical dynamics for the lineage, affecting the origin of multicellular life cycles, cell–cell communication, cellular differentiation, and multicellular morphogenesis. The types of intercellular bonds used by multicellular organisms may thus result in some of the most impactful historical constraints on the evolution of multicellularity. 

   more » « less
2. Metabolically-driven flows enable exponential growth in macroscopic multicellular yeast

   https://doi.org/10.1101/2024.06.19.599734  

   Narayanasamy, Nishant; Bingham, Emma; Fadero, Tanner; Bozdag, G Ozan; Ratcliff, William C; Yunker, Peter; Thutupalli, Shashi (June 2024, bioRxiv)

   The ecological and evolutionary success of multicellular lineages is due in no small part to their increased size relative to unicellular ancestors. However, large size also poses biophysical challenges, especially regarding the transport of nutrients to all cells; these constraints are typically overcome through multicellular innovations (e.g., a circulatory system). Here we show that an emergent biophysical mechanism — spontaneous fluid flows arising from metabolically-generated density gradients — can alleviate constraints on nutrient transport, enabling exponential growth in nascent multicellular clusters of yeast lacking any multicellular adaptations for nutrient transport or fluid flow. Surprisingly, beyond a threshold size, the metabolic activity of experimentally-evolved snowflake yeast clusters drives large-scale fluid flows that transport nutrients throughout the cluster at speeds comparable to those generated by the cilia of extant multicellular organisms. These flows support exponential growth at macroscopic sizes that theory predicts should be diffusion limited. This work demonstrates how simple physical mechanisms can act as a ‘biophysical scaffold’ to support the evolution of multicellularity by opening up phenotypic possibilities prior to genetically-encoded innovations. More broadly, our findings highlight how cooption of conserved physical processes is a crucial but underappreciated facet of evolutionary innovation across scales. 

   more » « less
3. The Evolution of Genetic Robustness for Cellular Cooperation in Early Multicellular Organisms

   https://doi.org/10.1162/isal_a_00536  

   Skocelas, Katherine G.; Ferguson, Austin J.; Bohm, Clifford; Perry, Katherine; Adaji, Rosemary; Ofria, Charles (July 2022, Proceedings of the 2022 Conference on Artificial Life)

   Holler, Silvia; Löffler, Richard; Bartlett, Stuart (Ed.)

   The major evolutionary transition to multicellularity shifted the unit of selection from individual cells to multicellular organisms. Constituent cells must regulate their growth and cooperate to benefit the whole organism, even when such behaviors would have been maladaptive were they free living. Mutations that disrupt cellular cooperation can lead to various ailments, including physical deformities and cancer. Organisms therefore employ mechanisms to enforce cooperation, such as error correction, policing, and genetic robustness. We built a simulation to study this last mechanism under a range of evolutionary conditions. Specifically, we asked: How does genetic robustness against cellular cheating evolve in multicellular organisms? We focused on early multicellular organisms (with only one cell type) where cells must control their growth to avoid overwriting each other. In our model, unrestrained cells will outcompete restrained cells within an organism, but restrained cells alone will result in faster reproduction for the organism. Ultimately, we demonstrate a clear selective pressure for genetic robustness in multicellular organisms and show that this pressure increases with the total number of cells in the organism. 

   more » « less
4. Metabolically driven flows enable exponential growth in macroscopic multicellular yeast

   https://doi.org/10.1126/sciadv.adr6399  

   Narayanasamy, Nishant; Bingham, Emma; Fadero, Tanner; Bozdag, G Ozan; Ratcliff, William C; Yunker, Peter; Thutupalli, Shashi (June 2025, Science Advances)

   The ecological and evolutionary success of multicellular lineages stems substantially from their increased size relative to unicellular ancestors. However, large size poses biophysical challenges, especially regarding nutrient transport: These constraints are typically overcome through multicellular innovations. Here, we show that an emergent biophysical mechanism—spontaneous fluid flows arising from metabolically generated density gradients—can alleviate constraints on nutrient transport, enabling exponential growth in nascent multicellular clusters of yeast lacking any multicellular adaptations for nutrient transport or fluid flow. Beyond a threshold size, the metabolic activity of experimentally evolved snowflake yeast clusters drives large-scale fluid flows that transport nutrients throughout the cluster at speeds comparable to those generated by ciliary actuation in extant multicellular organisms. These flows support exponential growth at macroscopic sizes that theory predicts should be diffusion limited. This demonstrates how simple physical mechanisms can act as a “biophysical scaffold” to support the evolution of multicellularity by opening up phenotypic possibilities before genetically encoded innovations. 

   more » « less
5. Lichens and microbial syntrophies offer models for an interdependent route to multicellularity

   https://doi.org/10.1017/S0024282921000256  

   Libby, Eric; Ratcliff, William C. (July 2021, The Lichenologist)

   Abstract The evolution of multicellularity paved the way for significant increases in biological complexity. Although multicellularity has evolved many times independently, we know relatively little about its origins. Directed evolution is a promising approach to studying early steps in this major transition, but current experimental systems have examined only a subset of the possible evolutionary routes to multicellularity. Here we consider egalitarian routes to multicellularity, in which unrelated unicellular organisms evolve to become a multicellular organism. Inspired by microbial syntrophies and lichens, we outline three such routes from a system of different species to an interdependent relationship that replicates. We compare these routes to contemporary experimental systems and consider how physical structure, the threat of invasion, division of labour and co-transmission affect their evolution. 

   more » « less