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Abstract The evolution of multicellularity represents a major transition in life’s history, enabling the rise of complex organisms. Multicellular groups can evolve through multiple developmental modes, but a common step is the formation of permanent cell–cell attachments after division. The characteristics of the multicellular morphology that emerges have profound consequences for the subsequent evolution of a nascent multicellular lineage, but little prior work has investigated these dynamics directly. Here, we examine a widespread yet understudied emergent multicellular morphology: cuboidal packing. Extinct and extant multicellular organisms across the tree of life have evolved to form groups in which spherical cells divide but remain attached, forming approximately cubic subunits. To experimentally investigate the evolution of cuboidal cell packing, we used settling selection to favor the evolution of simple multicellularity in unicellular, spherical Schizosaccharomyces pombe yeast. Multicellular clusters with cuboidal organization rapidly evolved, displacing the unicellular ancestor. These clusters displayed key hallmarks of an evolutionary transition in individuality: groups possess an emergent life cycle driven by physical fracture, group size is heritable, and they respond to group-level selection via multicellular adaptation. In 2 out of 5 lineages, group formation was driven by mutations in the ace2 gene, preventing daughter cell separation after division. Remarkably, ace2 mutations also underlie the transition to multicellularity in Saccharomyces cerevisiae and Candida glabrata, lineages that last shared a common ancestor >300 million years ago. Our results provide insight into the evolution of cuboidal cell packing, an understudied multicellular morphology, and highlight the deeply convergent potential for a transition to multicellular individuality within fungi.
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This content will become publicly available on February 18, 2026
Multiple pathways to the evolution of positive assortment in aggregative multicellularity
Abstract The evolutionary transition to multicellularity requires shifting the primary unit of selection from cells to multicellular collectives. How this occurs in aggregative organisms remains poorly understood. Clonal development provides a direct path to multicellular adaptation through genetic identity between cells, but aggregative organisms face a constraint: selection on collective-level traits cannot drive adaptation without positive genetic assortment. We leveraged experimental evolution of flocculatingSaccharomyces cerevisiaeto examine the evolution and role of genetic assortment in multicellular adaptation. After 840 generations of selection for rapid settling, 13 of 19 lineages evolved increased positive assortment relative to their ancestor. However, assortment provided no competitive advantage during settling selection, suggesting it arose as an indirect effect of selection on cell-level traits rather than through direct selection on collective-level properties. Genetic reconstruction experiments and protein structure modeling revealed two distinct pathways to assortment: kin recognition mediated by mutations in theFLO1adhesion gene and generally enhanced cellular adhesion that improved flocculation efficiency independent of partner genotype. The evolution of assortment without immediate adaptive benefit suggests that key innovations enabling multicellular adaptation may arise indirectly through cell-level selection. Our results demonstrate fundamental constraints on aggregative multicellularity and help explain why aggregative lineages have remained simple.
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- Award ID(s):
- 1845363
- PAR ID:
- 10584988
- Publisher / Repository:
- bioRxiv
- Date Published:
- Format(s):
- Medium: X
- Institution:
- bioRxiv
- Sponsoring Org:
- National Science Foundation
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