VI. Earth Life Emergence: Development of Body, Brain, Selves and Societies

5. Multicellular Fauna and Flora Organisms

Sole, Ricard, et al. The Road to Synthetic Multicellularity. Current Opinion in Systems Biology. 7/60, 2018. Universitat Pompeu Fabra, Barcelona, and University of Birmingham, UK scientists scope out a project map which scans the journey so far along with a route ahead to spatial patterns, developmental programs, proto-organisms, embodied evolved multicellularity, and long-term evolution via synthetic ecosystems projects. See also, e.g. Model Microbial Communities for Ecosystems Biology in this journal (6/51, 2017).

Multicellularity is a crucial innovation that has taken place independently at least 25 times in the evolution of life on our planet. Uncovering the evolutionary rules associated to the emergence of this transition has been partially achieved thanks to a combination of comparative cell biology, phylogenetic, palaeobiology and genomic studies of primitive model organisms. An alternative path to this goal is the use of synthetic and systems approximations including both experimental and mathematical models. Here we review several key results, formulate a list of open problems and suggest potentially relevant avenues to follow at the crossroads between ecology, evolution and development. (Abstract)

Trewavas, Anthony. The Green Plant as an Intelligent Organism. Baluska, Frantisek, et al, eds. Communication in Plants. Berlin: Springer, 2006. The University of Edinburgh botanist finds a responsive cognitive capacity across the flora kingdoms similarly distinguished by information processing, learning, decision making, choice, predictive modeling, associative memory, sensory integration, and behavioral control. See also a similar article in Trends in Plant Science for September 2005.

Van Gestel, Jordi and Corina Tarnita. On the Origin of Biological Construction, with a Focus on Multicellularity. Proceedings of the National Academy of Sciences. 114/11018, 2017. As the major evolutionary transitions model (see Section VI.H.8) steadily gains acceptance, akin to Sebe-Pedros 2017, University of Zurich and Princeton University systems biologists and ecologists (search each) add a more detailed explanation of how simpler individual organic forms may proceed to join and merge into complex, aggregate whole units. A generic, common life cycle is specified which contributes a perception of the same, independent pattern of diversity, convergence and emergence at work for each nested stage, as the Abstract alludes. A hundred references are cited in support. So in late 2017, unawares as yet, a genesis synthesis becomes robustly evident.

Biology is marked by a hierarchical organization: all life consists of cells; in some cases, these cells assemble into groups, such as endosymbionts or multicellular organisms; in turn, multicellular organisms sometimes assemble into yet other groups, such as primate societies or ant colonies. The construction of new organizational layers results from hierarchical evolutionary transitions, in which biological units (e.g., cells) form groups that evolve into new units of biological organization (e.g., multicellular organisms). Despite considerable advances, there is no bottom-up, dynamical account of how, starting from the solitary ancestor, the first groups originate and subsequently evolve the organizing principles that qualify them as new units.

Guided by six central questions, we propose an integrative bottom-up approach for studying the dynamics underlying hierarchical evolutionary transitions, which builds on and synthesizes existing knowledge. This approach highlights the crucial role of the ecology and development of the solitary ancestor in the emergence and subsequent evolution of groups, and it stresses the paramount importance of the life cycle: only by evaluating groups in the context of their life cycle can we unravel the evolutionary trajectory of hierarchical transitions. The central research questions outlined here naturally link existing research programs on biological construction (e.g., on cooperation, multilevel selection, self-organization, and development) and thereby help integrate knowledge stemming from diverse fields of biology. (Abstract)

Van Gestel, Jordi, et al. From Cell Differentiation to Cell Collectives: Bacillus subtilis Uses Division of Labor to Migrate. PLoS Biology. Online April, 2015. In one more quantification of nature’s propensity to give rise to viable groupings, Harvard Medical School biologists propose this title phenomena as a key factor underlying the diverse origins of multicellularity. A June 2015 review Bacterial Ventures into Multicellularity: Collectivism through Individuality by Simon van Vliet and Martin Ackermann in this journal extols the significance of these research findings. See similar works by Kapheim, Rehan, C. Smith, and others.

Some problems can be solved only when individuals act together. This applies to bacteria in the same way that it applies to humans. Here we study how bacteria overcome the environmental challenge of migration over a solid surface by bundling their forces. Migration can be a significant environmental challenge for bacteria, especially when food sources are distributed far apart and have to be reached by movement along a solid surface, where swimming motility does not work. We show that Bacillus subtilis—a common inhabitant of the soil—migrates over a solid surface by forming multicellular structures. Migration depends on the synergistic interaction of two cell types: surfactin-producing and matrix-producing cells. Surfactin-producing cells facilitate migration by reducing the friction between cells and their substrate, thereby allowing matrix-producing cells to organize themselves into bundles that form filamentous loops at the colony edge. Thus, not only do cells act together to overcome the challenge of migration, they also divide labor, in that different cell types specialize on distinct tasks. (Author Summary)

Like other forms of bacterial multicellularity, van Gogh bundles illustrate how the organization of cells can help to overcome important ecological challenges. Ultimately, we hope that the study of such simple forms of organization can improve our understanding on how evolution constructs: how cells can evolve to become integrated collectives that, together, form a new organizational unit. (17)

Von Bronk, Benedikt, et al. Complex Microbial Systems across Different Level of Description. Physical Biology. Online June, 2018. Ludwig-Maximilians University, Soft Condensed Matter Group researchers study bacterial colonies as exemplars of nonlinear dynamics and topologies, as the late Israeli biophysicst Eshel Ben-Jacob, whose image opens this section, had long advocated. In regard, over the 21st century posting this website, it is can now be reported that every other realm from quantum to literature has been found to match and fulfill this iconic model.

Complex biological systems offer a variety of interesting phenomena at the different physical scales. With increasing abstraction, details of the microscopic scales can often be extrapolated to average or typical macroscopic properties. However, emergent properties and cross-scale interactions can impede naïve abstractions and necessitate comprehensive investigations of these complex systems. In this review paper, we focus on microbial communities, and first, summarize a general hierarchy of relevant scales and description levels to understand these complex systems: (1) genetic networks, (2) single cells, (3) populations, and (4) emergent multi-cellular properties. Second, we employ two illustrating examples, microbial competition and biofilm formation, to elucidate how cross-scale interactions and emergent properties enrich the observed multi-cellular behavior in these systems. (Abstract)

Wedlich-Soldner, Roland and Timo Betz. Self-Organization: The Fundament of Cell Biology. Philosophical Transactions of the Royal Society B.. Vol.373/Iss.1747, 2018. We enter this introductory note by University of Munster, Cells in Motion Cluster of Excellence, systems scientists both for the special issue, and as the Abstract cites, an example of how into the 2010s nonlinear complex systems dynamics have actuallybecome accepted as a mainstream explanatory paradigm. Among the papers are Self-Organization across Scales: From Molecules to Organisms by Tanumoy Saha and Milos Galic and Self-Organization Principles of Intracellular Pattern Formation by Jacob Halatek, et al (reviewed herein).

Self-organization refers to the emergence of an overall order in time and space of a given system that results from the collective interactions of its individual components. This concept has been widely recognized as a core principle in pattern formation for multi-component systems of the physical, chemical and biological world. It can be distinguished from self-assembly by the constant input of energy required to maintain order—and self-organization therefore typically occurs in non-equilibrium or dissipative systems. Cells, with their constant energy consumption and myriads of local interactions between distinct proteins, lipids, carbohydrates and nucleic acids, represent the perfect playground for self-organization. It therefore comes as no surprise that many properties and features of self-organized systems, such as spontaneous formation of patterns, nonlinear coupling of reactions, bi-stable switches, waves and oscillations, are found in all aspects of modern cell biology. Ultimately, self-organization lies at the heart of the robustness and adaptability found in cellular and organismal organization, and hence constitutes a fundamental basis for natural selection and evolution. (Abstract)

Wilkins, Adam. The Evolution of Developmental Pathways. Sunderland, MA: Sinauer, 2002. A contribution to the resurgence of evolutionary developmental biology.

Woese, Carl. Interperting the Universal Phylogenetic Tree. Proceedings of the National Academy of Sciences. 97/8392, 2000. A review of the past history and present clarifications in specifying the three kingdoms of life with their common root and branches to plants and animals.

The above theory makes a testable prediction: the ancestors of the individual domains - the Bacteria, the Archaea, and the eukaryotes - are each communal, and the evidence for their communal nature, in the form of elevated levels of horizontal gene transfer within each domain early on (i.e., transfer involving the ancestors of the major taxa), should still exist. (8395)

Xing, Jianhua, et al. Computational Cell Biology. Interface Focus. 4/20140027, 2014. Virginia Tech and University of Cincinnati scientists introduce a special issue as another example of the on-going evolutionary revolution to better understand organismic life by virtue of equally real, independent, pervasive dynamic, modular, network and systems phenomena. A notable paper is It is Not the Parts, but How They Interact that Determines the Behavior of Circadian Rhythms across Scales and Organisms by Dan DeWoskin, et al.

As in physics and chemistry long ago, molecular life sciences are undergoing a foundational revision from empirical to mathematical. This trend has been prompted by insufficiency of the reductionist approach to provide quantitative explanations and predictions for the properties of molecular regulatory systems, whose observed behaviours are typically emergent phenomena governed by interactions between multiple components. A now classical example of this situation is the study of biological oscillations, such as circadian rhythms and the cell cycle, where the most significant properties of oscillation (period, amplitude, robustness, etc.) are non-trivially related in general to the details of the underlying network.

Yamagishi, Jumpei, et al. Symbiotic Cell Differentiation and Cooperative Growth in Multicellular Aggregates. PLoS Computational Biology. Online October, 2016. With Neri Salto and Kunihiko Kaneko, University of Tokyo biologists advance their studies of life’s persistent symbiosis of entity and assembly, which here is seen to foster nested stages of beneficial complexities and an emergent evolution. In this case, generic developmental systems theory explains how such groupings become wholly viable through reciprocal divisions of labor. See also Prof. Kaneko’s chapter in the 2016 volume Multicellularity (search Niklas).

Unicellular organisms, when aggregated under limited resources, often exhibit behaviors akin to multicellular organisms, possibly without advanced regulation mechanisms, as observed in biofilms and bacterial colonies. Cells in an aggregate have to differentiate into several types that are specialized for different tasks, so that the growth rate should be enhanced by the division of labor among these cell types. To consider how a cell aggregate can acquire these properties, most theoretical studies have thus far assumed the fitness of an aggregate of cells and the ability of cell differentiation a priori. In contrast, we developed a dynamical-systems model consisting of cells without assuming predefined fitness. The model consists of catalytic-reaction networks for cellular growth. By extensive simulations and theoretical analysis of the model, we showed that cells growing under the condition of nutrient limitation and strong cell-cell interactions can differentiate with distinct chemical compositions. They achieve cooperative division of labor by exchanging the produced chemicals to attain a higher growth rate. The conditions for spontaneous cell differentiation and collective growth of cells are presented. The uncovered symbiotic differentiation and collective growth are akin to economic theory on division of labor and comparative advantage. (Summary)

Zimmer, Carl. At the Water’s Edge: Macroevolution and the Transformation of Life. New York: The Free Press, 1998. The narrative story of the transition from fish to tetrapod and from land mammal to whales.

Zimmer, Carl. The Tangled Bank: An Introduction to Evolution. Greenwood Village, CO: Roberts and Co, 2009. A beautifully organized, illustrated and written text tour of the grandeur of Darwinian naturally living systems.

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