VI. Earth Life Emergence: Development of Body, Brain, Selves and Societies
5. Multicellular Fauna and Flora Organisms
Gilbert, Scott and Jessica Bolker. Homologies of Process and Modular Elements of Embryonic Construction. Journal of Experimental Zoology. 291/1, 2001. A Bauplan (archetypal body form) is invoked along with common dynamical systems which employ semi-autonomous modules for their processes of organic development.
Grosberg, Richard and Richard Strathmann. The Evolution of Multicellularity: A Minor Major Transition? Annual Review of Ecology, Evolution, and Systematics. 38/621, 2007. University of Washington biologists expand on the now accepted view of an evolutionary sequence posed by the late John Maynard Smith and Eors Szathmary by discussing how myriad genetic and cellular phenomena contribute to this progressive emergence. The merger of nucleated cells into rudimentary organisms is seen as occurring many times, so it is said to be ‘relatively easy.’ By what perspective or project then could the oriented procession that the quote describes be taken as evidence of an innate self-organizing propensity, for this is just the repetitive scale that it would produce?
Beneath the outward harmony of living organisms lies an often contentious history of transitions to ever more inclusive, hierarchically nested levels of biological organization. Although views differ on what defines a major evolutionary transition, almost everyone agrees that the following transitions qualify as major: (a) the compartmentalization of replicating molecules, yielding the first cells; (b) the coalescence of replicating molecules to form chromosomes; (c) the use of DNA and proteins as the fundamental elements of the genetic code and replication; (d) the consolidation of symbiotic cells to generate the first eukaryotic cells containing chloroplasts and mitochondria; (e) sexual reproduction involving the production (by Meiosis) and fusion of haploid gametes: (f) the evolution of multicellular organisms from unicellular ancestors; and (g) the establishment of social groups composed of discrete multicellular individuals. (622)
Grossnickle, David, et al. Untangling the Multiple Ecological Radiations of Early Mammals. Trends in Ecology and Evolution. Online June, 2019. DG and Gregory Wilson, University of Washington along with Stephanie Smith, Field Museum of Natural History, Chicago, provide an extensive illustrated survey of our latest collective reconstruction of how life’s myriad creaturely species evolved and emerged. We muse and wonder whatever phenomenal contribution are we homo to Anthropo sapiens here by achieving for a self-revealing and auto-creating ecosmos.
The ecological diversification of early mammals is a globally transformative event in Earth’s history, largely due to the Cretaceous Terrestrial Revolution mass extinction. A confounding issue is that it comprised nested radiations of mammalian subclades within the broader scope of their evolution. In the past 200 million years, various independent groups experienced large-scale radiations involving ecological diversification from ancestral lineages of small insectivores such as include Jurassic mammalia forms, Late Cretaceous metatherians, and Cenozoic placentals. Here, we review these speciations which reveal the nuanced complexity of early mammal evolution, the value of ecomorphological fossil data, and phylogenetic context in macroevolutionary studies. (Abstract)
Halatek, Jacob, et al. Self-Organization Principles of Intracellular Pattern Formation. Philosophical Transactions of the Royal Society B. Vol.373/Iss.1747, 2018. In a technical paper, Ludwig Maximilian University, Munich biophysicists including Erwin Frey contribute to 21st century verifications of the presence, as long intimated (second quote), of nature’s propensity to form nested viable units of many members within reciprocal wholes. Circa 2018 this innate form and function can be quantified in detailed fashion by way of autocatalytic conversions via activator-inhibitor dynamics. See also Rethinking Pattern Formation in Reaction-Diffusion Systems by Halatek and Frey in Nature Physics (February 2018) and MinE Conformational Switching Confers Robustness on Self-Organized Min Protein Patterns in PNAS (115/4553, 2018). We note that since this multi-cellular section was posted in 2004 the presence of innate self-organized biological processes has moved from a remote idea to these theoretical confirmations.
Dynamic patterning of specific proteins is essential for the spatio-temporal regulation of many important intracellular processes in prokaryotes, eukaryotes and multicellular organisms. In this article, we review quantitative models for intracellular Min protein patterns in Escherichia coli, Cdc42 polarization in Saccharomyces cerevisiae and the bipolar PAR protein patterns found in Caenorhabditis elegans. By analysing the molecular processes driving these systems we derive general principles underlying self-organized pattern formation. Mass-conserving reaction–diffusion equations provide the most appropriate framework to study intracellular pattern formation. We conclude that directed transport, e.g. cytosolic diffusion along an actively maintained cytosolic gradient, is the key process underlying pattern formation. Thus the basic principle of self-organization is the establishment and maintenance of directed transport by intracellular protein dynamics. (Abstract excerpt)
Hammerschmidt, Katrin, et al. Life Cycles, Fitness Decoupling and the Evolution of Multicellularity. Nature. 515/75, 2014. Massey University, Auckland, and University of Washington, Seattle, researchers including Paul Rainey continue to quantify and explain how relative unicellular stages proceed to merge into organism forms of benefit both to member and the new individual. By so doing it is said that Darwinian selection processes shift by way of collective reproduction to this higher level. The surmise is a natural persistence for life to combine into whole nested entities by a ratcheted repetition.
Cooperation is central to the emergence of multicellular life; however, the means by which the earliest collectives (groups of cells) maintained integrity in the face of destructive cheating types is unclear. One idea posits cheats as a primitive germ line in a life cycle that facilitates collective reproduction. Here we describe an experiment in which simple cooperating lineages of bacteria were propagated under a selective regime that rewarded collective-level persistence. Collectives reproduced via life cycles that either embraced, or purged, cheating types. When embraced, the life cycle alternated between phenotypic states. Selection fostered inception of a developmental switch that underpinned the emergence of collectives whose fitness, during the course of evolution, became decoupled from the fitness of constituent cells. Our findings capture key events in the evolution of Darwinian individuality during the transition from single cells to multicellularity. (Abstract)
Herron, Matthew, et al. Genetics of a de Novo Origin of Undifferentiated Multicellularity. Royal Society Open Science. August, 2018. Georgia Tech biologists Herron, William Ratcliff, Jacob Boswell and Frank Rosenzweig post one more quantification of how inevitable and insistent life’s evolutionary emergence from single eukaryote cells to complex organisms seems to be. And this scalar step may be the most significant advance, since all subsequent organisms including us followed from its occasion.
The evolution of multicellularity was a major transition in evolution and set the stage for unprecedented increases in complexity, especially in land plants and animals. Here, we explore the genetics underlying a de novo origin of multicellularity in a microbial evolution experiment carried out on the green alga Chlamydomonas reinhardtii. We show that large-scale changes in gene expression underlie the transition to a multicellular life cycle. These results suggest that the genetic basis for the experimental evolution of multicellularity in C. reinhardtii has both lineage-specific and shared features, and that the shared features have more in common with C. reinhardtii's relatives among the volvocine algae than with other multicellular green algae or land plants. (Abstract)
Hou, Chen, et al. Energetic Basis of Colonial Living in Social Insects. Proceedings of the National Academy of Science. 107/3634, 2010. Researchers from New York, Florida, Oklahoma, and Panama find the same anatomical and physiological relations to recur for both organisms themselves, and for viable colonial groupings they may reside in. Such deep, broad recurrence then implies an unavoidable sign of life’s evolution as an inherently convergent process.
Metabolic scaling theory, based largely on the body mass scaling of metabolic rate, has successfully predicted many aspects of the physiology and life history of individual (or unitary) organisms. Here we show, using a diverse set of social insect species, that this same theory predicts the size dependence of basic features of the physiology (i.e., metabolic rate, reproductive allocation) and life history (i.e., survival, growth, and reproduction) of whole colonies. The similarity in the size dependence of these features in unitary organisms and whole colonies points to commonalities in functional organization. Thus, it raises an important question of how such evolutionary convergence could arise through the process of natural selection. (3634)
Ingber, Donald. The Architecture of Life. Scientific American. January, 1998. A universal set of self-assembly rules hold for and give rise to a bodily anatomy “organized hierarchically as tiers of systems within systems.” The author muses in closing that through achievements such as tensegrity geometry evident in protein structures, we are finally reading the book of nature foretold by Plato and Galileo.
Ispolatov, Iaroslav, et al. Division of Labour and the Evolution of Multicellularity. Proceedings of the Royal Society B. 279/1768, 2012. University of British Columbia, and ETH Zurich, theoretical microbiologists find the common, beneficial propensity of evolving groups from microbes to neighborhoods to spontaneously divide functional tasks to be similarly present as cells join into viable multicellular assemblies.
Understanding the emergence and evolution of multicellularity and cellular differentiation is a core problem in biology. We develop a quantitative model that shows that a multicellular form emerges from genetically identical unicellular ancestors when the compartmentalization of poorly compatible physiological processes into component cells of an aggregate produces a fitness advantage. This division of labour between the cells in the aggregate occurs spontaneously at the regulatory level owing to mechanisms present in unicellular ancestors and does not require any genetic predisposition for a particular role in the aggregate or any orchestrated cooperative behaviour of aggregate cells. Mathematically, aggregation implies an increase in the dimensionality of phenotype space that generates a fitness landscape with new fitness maxima, in which the unicellular states of optimized metabolism become fitness saddle points. Evolution of multicellularity is modelled as evolution of a hereditary parameter: the propensity of cells to stick together, which determines the fraction of time a cell spends in the aggregate form. Stickiness can increase evolutionarily owing to the fitness advantage generated by the division of labour between cells in an aggregate. (Abstract)
Jacobeen, Shane, et al. Cellular Packing, Mechanical Stress and the Evolution of Multicellularity. Nature Physics. 14/3, 2018. Georgia Tech biophysicists including William Ratcliff consider these physical and structural features which seem to facilitate how bunching cell communities to could rise into beneficial composite compartments. See also Nascent Life Cycles and the Emergence of Higher-Level Individuality by Ratcliff, et al.
The evolution of multicellularity set the stage for sustained increases in organismal complexity. However, a fundamental aspect of this transition remains largely unknown: how do simple clusters of cells evolve increased size when confronted by forces capable of breaking intracellular bonds? Here we show that multicellular snowflake yeast clusters fracture due to crowding-induced mechanical stress. Over seven weeks of daily selection for large size, snowflake clusters evolve to increase their radius 1.7-fold by reducing the accumulation of internal stress. This work demonstrates how readily natural selection finds simple, physical solutions to spatial constraints that limit the evolution of group size—a fundamental step in the evolution of multicellularity. (Abstract)
Jung, Heekyung, et al. The Ancient Origins of Neural Substrates for Land Walking. Cell. 172/4, 2018. In a paper noted in the New York Science Times, an eleven member team from the USA, Australia, and Singapore, based at NYU School of Medicine, describe for the first time a rudimentary neural basis for the transition from an aquatic phase to mobile terrestrial creatures. As a surmise, it would appear that this fins to feet procession seems written into life’s oriented evolutionary advance.
Walking is the predominant locomotor behavior expressed by land-dwelling vertebrates, but it is unknown when the neural circuits that are essential for limb control first appeared. Certain fish species display walking-like behaviors, raising the possibility that the underlying circuitry originated in primitive marine vertebrates. We show that the neural substrates of bipedalism are present in the little skate Leucoraja erinacea, whose common ancestor with tetrapods existed ∼420 million years ago. Leucoraja exhibits core features of tetrapod locomotor gaits, including left-right alternation and reciprocal extension-flexion of the pelvic fins. This network encodes peripheral connectivity modules that are distinct from those used in axial muscle-based swimming and has apparently been diminished in most modern fish. These findings indicate that the circuits that are essential for walking evolved through adaptation of a genetic regulatory network shared by all vertebrates with paired appendages. (Abstract)
Kaiser, Dale. Building a Multicellular Organism. Annual Review of Genetics. 35/103, 2001. The same process of symbiosic association occurs in the formation of an organism as it did when diverse bacteria evolved and joined to form nucleated cells.
Multicellular organisms appear to have arisen from unicells numerous times. Multicellular cyanobacteria arose early in the history of life on Earth. Multicellular forms have since arisen independently in each of the kingdoms and several times in some phyla. If the step from unicellular to multicellular life was taken early and frequently, the selective advantage of multicellularity may be large….The capacity for signaling between cells accompanies the evolution of multicellularity with cell differentiation. (103)