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- 18.0: Introduction
- This page examines social behaviors in cells of multicellular organisms, highlighting evolutionary links across species and the importance of studying diverse organisms. It discusses mechanisms like quorum sensing, self-sacrifice, and temporary multicellular structures. Although molecular mechanisms differ, similar processes underlie essential behaviors for development and system integration, particularly in the immune system and brain.
- 18.1: How do unicellular organisms generate phenotypic diversity?
- This page explores cell division in unicellular organisms, primarily Caulobacter crescentus, highlighting the lifecycle of swarmer cells and their transition from motility to anchoring. It introduces deterministic phenotypic switching and stochastic processes that generate variability among genetically identical cells, helping populations adapt to environmental changes. This adaptability leads some cells to enter dormancy or form spores for survival, enhancing evolutionary resilience.
- 18.2: Dying for others – social interactions between “unicellular” organisms
- This page discusses the prevalence of self-sacrificing behaviors in biological systems, challenging traditional evolutionary views. It highlights examples like cyanobacteria, where some cells become heterocysts to benefit neighboring cells, thereby enhancing population fitness, especially under stress conditions like viral infections. The page emphasizes that such social behaviors can improve survival and evolutionary success through mechanisms of inclusive fitness.
- 18.3: Quorum effects (somewhat redundant)
- This page discusses how certain behaviors in organisms become beneficial only when population density surpasses a critical threshold, highlighting the example of Anabaena cells. As populations increase, cooperative behaviors emerge, leading to better resource acquisition. However, the presence of cheaters poses a threat to altruism, prompting the evolution of strategies to uphold social cooperation and enhance group survival in the face of environmental challenges.
- 18.4: Transient and clonal ("true") metazoans
- This page explores developmental processes in organisms with unicellular and transient multicellular states, focusing on transient metazoans. It underscores the significance of cooperation among single-celled organisms, facilitating complex behaviors.
- 18.5: Unicellular to multicellularity to unicellularity
- This page explores quorum sensing and internal signaling in Dictyostelium discoideum, which allow these single-celled organisms to respond to environmental changes by forming multicellular structures known as slugs. It highlights how they use signaling systems like pre-starvation factors and cyclic AMP to facilitate migration, aggregation, and differentiation during adverse conditions, ensuring survival.
- 18.6: Evolutionary origins of clonal (permanent) multicellularity
- This page examines the evolution of multicellularity, particularly in social slime molds, noting critical transitions likely happened during the Cryogenian period. It discusses how factors like predator avoidance and ecological efficiency drive multicellularity.
This page titled 18: Supplemental Chapter - Social interactions between cells was last modified on Thu, 08 Jan 2026 22:57:29 GMT and is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Michael W. Klymkowsky and Melanie M. Cooper.
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