More Like this

1. 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
2. Oxygen suppression of macroscopic multicellularity

   https://doi.org/10.1038/s41467-021-23104-0  

   Bozdag, G. Ozan; Libby, Eric; Pineau, Rozenn; Reinhard, Christopher T.; Ratcliff, William C. (December 2021, Nature Communications)

   null (Ed.)

   Abstract Atmospheric oxygen is thought to have played a vital role in the evolution of large, complex multicellular organisms. Challenging the prevailing theory, we show that the transition from an anaerobic to an aerobic world can strongly suppress the evolution of macroscopic multicellularity. Here we select for increased size in multicellular ‘snowflake’ yeast across a range of metabolically-available O 2 levels. While yeast under anaerobic and high-O 2 conditions evolved to be considerably larger, intermediate O 2 constrained the evolution of large size. Through sequencing and synthetic strain construction, we confirm that this is due to O 2 -mediated divergent selection acting on organism size. We show via mathematical modeling that our results stem from nearly universal evolutionary and biophysical trade-offs, and thus should apply broadly. These results highlight the fact that oxygen is a double-edged sword: while it provides significant metabolic advantages, selection for efficient use of this resource may paradoxically suppress the evolution of macroscopic multicellular organisms. 

   more » « less
3. Emergence and maintenance of stable coexistence during a long-term multicellular evolution experiment

   https://doi.org/10.1038/s41559-024-02367-y  

   Pineau, Rozenn M; Libby, Eric; Demory, David; Lac, Dung T; Day, Thomas C; Bravo, Pablo; Yunker, Peter J; Weitz, Joshua S; Bozdag, G Ozan; Ratcliff, William C (May 2024, Nature Ecology & Evolution)

   The evolution of multicellular life spurred evolutionary radiations, fundamentally changing many of Earth’s ecosystems. Yet little is known about how early steps in the evolution of multicellularity affect eco-evolutionary dynamics. Through long-term experimental evolution, we observed niche partitioning and the adaptive divergence of two specialized lineages from a single multicellular ancestor. Over 715 daily transfers, snowflake yeast were subjected to selection for rapid growth, followed by selection favouring larger group size. Small and large cluster-forming lineages evolved from a monomorphic ancestor, coexisting for over ~4,300 generations, specializing on divergent aspects of a trade-off between growth rate and survival. Through modelling and experimentation, we demonstrate that coexistence is maintained by a trade-off between organismal size and competitiveness for dissolved oxygen. Taken together, this work shows how the evolution of a new level of biological individuality can rapidly drive adaptive diversification and the expansion of a nascent multicellular niche, one of the most historically impactful emergent properties of this evolutionary transition. 

   more » « less
4. Nitrogen isotopic constraints on nutrient transport to the upper ocean

   https://doi.org/10.1038/s41561-021-00836-8  

   Fripiat, François; Martínez-García, Alfredo; Marconi, Dario; Fawcett, Sarah E.; Kopf, Sebastian H.; Luu, Victoria H.; Rafter, Patrick A.; Zhang, Run; Sigman, Daniel M.; Haug, Gerald H. (November 2021, Nature Geoscience)

   Abstract Ocean circulation supplies the surface ocean with the nutrients that fuel global ocean productivity. However, the mechanisms and rates of water and nutrient transport from the deep ocean to the upper ocean are poorly known. Here, we use the nitrogen isotopic composition of nitrate to place observational constraints on nutrient transport from the Southern Ocean surface into the global pycnocline (roughly the upper 1.2 km), as opposed to directly from the deep ocean. We estimate that 62 ± 5% of the pycnocline nitrate and phosphate originate from the Southern Ocean. Mixing, as opposed to advection, accounts for most of the gross nutrient input to the pycnocline. However, in net, mixing carries nutrients away from the pycnocline. Despite the quantitative dominance of mixing in the gross nutrient transport, the nutrient richness of the pycnocline relies on the large-scale advective flow, through which nutrient-rich water is converted to nutrient-poor surface water that eventually flows to the North Atlantic. 

   more » « less
5. Varied solutions to multicellularity: the biophysical and evolutionary consequences of diverse intercellular bonds

   Day, Thomas C.; Márquez-Zacarías, Pedro; Bravo, Pablo; Pokhrel, Aawaz R.; MacGillivray, Kathryn; Ratcliff, William C.; Yunker, Peter J. (July 2022, Biophysics reviews)

   The diversity of multicellular organisms is, in large part, due to the fact that multicellularity has evolved many times independently. 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 re-formable, or they are not. Both classes of multicellular assembly are common in nature, having evolved dozens of times independently. 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