VI. Earth Life Emergence: Development of Body, Brain, Selves and Societies
5. Multicellular Fauna and Flora Organisms
Niklas, Karl and Stuart Newman. The Origins of Multicellular Organisms. Evolution & Development. 15/1, 2013. The Cornell University plant biologist and New York Medical College cell biologist provide a current update of the persistent course of unicellular life to form more complex creatures in similar self-organized, symbiotic ways as they became whole entities.
Multicellularity has evolved in several eukaryotic lineages leading to plants, fungi, and animals. Theoretically, in each case, this involved (1) cell-to-cell adhesion with an alignment-of-fitness among cells, (2) cell-to-cell communication, cooperation, and specialization with an export-of-fitness to a multicellular organism, and (3) in some cases, a transition from “simple” to “complex” multicellularity. When mapped onto a matrix of morphologies based on developmental and physical rules for plants, these three phases help to identify a “unicellular colonial filamentous (unbranched branched) pseudoparenchymatous parenchymatous” morphological transformation series that is consistent with trends observed within each of the three major plant clades. In contrast, a more direct “unicellular colonial or siphonous parenchymatous” series is observed in fungal and animal lineages. In these contexts, we discuss the roles played by the cooptation, expansion, and subsequent diversification of ancestral genomic toolkits and patterning modules during the evolution of multicellularity. (Summary)
Niklas, Karl and Stuart Newman, eds. Multicellularity: Origins and Evolution. Cambridge: MIT Press, 2016. A collection from a September 2014 conference at the Konrad Lorenz Institute in Austria on persistent evolutionary transitions from simpler unicellular forms to the multiple complexities of cellular organisms. Discussions covered the span of genetic to environmental to philosophic aspects of life’s insistent drive and propensity to develop entities within encompassing biological wholes. Typical papers are Fossils, Feeding, and the Evolution of Complex Multicellularity by Andrew Knoll and Daniel Lahr, Cellular Slime Mold Development by Vidyanand Nanjundiah, and A Scenario for the Origin of Multicellular Organisms: Perspective from Multilevel Consistency Dynamics by Kunihiko Kaneko.
The evolution of multicellularity raises questions regarding genomic and developmental commonalities and discordances, selective advantages and disadvantages, physical determinants of development, and the origins of morphological novelties. It also represents a change in the definition of individuality, because a new organism emerges from interactions among single cells. The contributors consider the fossil record of the paleontological circumstances in which animal multicellularity evolved; cooptation, recurrent patterns, modularity, and plausible pathways for multicellular evolution in plants; theoretical approaches to the amoebozoa and fungi (cellular slime molds having long provided a robust model system for exploring the evolution of multicellularity), plants, and animals; genomic toolkits of metazoan multicellularity; and philosophical aspects of the meaning of individuality in light of multicellular evolution. (Publisher)
O’Leary, Maureen. On the Trail of the First Placental Mammals. American Scientist. May/June, 2014. The SUNY Stony Brook, School of Medicine, professor of Anatomical Sciences and director of the MorphoBank Project for Phylogenetic Research describes the latest worldwide reconstruction of the myriad critters and creatures across evolutionary stages and kingdoms, which is now graphically online at morphobank.org. And if to reflect, who are we Anthropo Sapiens to so emerge from and altogether be able to retrospectively view from whence we came? What kind of universe wants and needs to achieve its own self-conscious description?
Olimpio, Eduardo, et al. Statistical Dynamics of Spatial-Order Formation by Communicating Cells. iScience. 2/27, 2018. In this new Cell Press open journal, a team of Delft University of Technology, Kavli Institute of Nanoscience, biophysicists continue to join life’s dynamic evolutionary cellularity with its natural rootings in condensed matter mechanics.
Communicating cells can coordinate their gene expressions to form spatial patterns, generating order from disorder. Here we present a modeling framework based on cellular automata and mimicking approaches of statistical mechanics for understanding how secrete-and-sense cells with bistable gene expression, from disordered beginnings, can become spatially ordered by communicating through rapidly diffusing molecules. Classifying lattices of cells by two “macrostate” variables reveals a conceptual picture: a group of cells behaves as a single particle that rolls down on an adhesive “pseudo-energy landscape” whose shape is determined by cell-cell communication and an intracellular gene-regulatory circuit. (Abstract excerpts)
Pagel, Mark, ed. Encyclopedia of Evolution. Oxford: Oxford University Press, 2002. A two volume compendium of the fossil and gene based standard Darwinian theory, but as so many fragments with no sense of anything going on. As an example, emergent brain development gets four pages out of more than twelve hundred.
Parfrey, Laura Wegener and Daniel Lahr. Multicellularity Arose Several Times in the Evolution of Eukaryotes. BioEssays. 35/4, 2013. University of Colorado and University of Sao Paulo system zoologists contribute to findings of a “strikingly similar” impetus and tendency across flora and fauna to evolve and join into increasing complex organismic assemblies. This propensity then converges in a way that repeats in kind the biomolecular mechanisms of its unicellular ancestors.
The cellular slime mold Dictyostelium has cell-cell connections similar in structure, function, and underlying molecular mechanisms to animal epithelial cells. These similarities form the basis for the proposal that multicellularity is ancestral to the clade containing animals, fungi, and Amoebozoa (including Dictyostelium): Amorphea (formerly “unikonts”). This hypothesis is intriguing and if true could precipitate a paradigm shift. However, phylogenetic analyses of two key genes reveal patterns inconsistent with a single origin of multicellularity. A single origin in Amorphea would also require loss of multicellularity in each of the many unicellular lineages within this clade. Further, there are numerous other origins of multicellularity within eukaryotes, including three within Amorphea, that are not characterized by these structural and mechanistic similarities. Instead, convergent evolution resulting from similar selective pressures for forming multicellular structures with motile and differentiated cells is the most likely explanation for the observed similarities between animal and dictyostelid cell-cell connections. (Abstract)
Pennisi, Elizabeth. The Power of Many. Science. 360/1388, 2018. A series of simple steps can explain the momentous transition from single cells to multicellular life. A science journalist gathers the work of Laszlo Nagy, Ben Kerr, Nicole King, Nicholas Butterfield, William Ratcliff and others to report new findings about how this evolutionary ascent unto complex organisms seems meant to readily proceed. An innate natural affinity for rudimentary cells to band together, repurpose, diversify, divide labor, and more so to gain group level benefits appears to be written in.
Pfeiffer, Thomas and Sebastian Bonhoeffer. An Evolutionary Scenario for the Transition to Undifferentiated Multicellularity. Proceedings of the National Academy of Sciences. 100/1095, 2003. The initial phase in this emergence is seen as the formation of simple, undifferentiated cell clusters wherein cooperative behavior became more advantageous for survival than competition.
The first step in the evolutionary transition to multicellularity likely was the evolution of simple, undifferentiated cell clusters….Here we argue that in populations of unicellular organisms with cooperative behavior, clustering may be beneficial by reducing interactions with noncooperative individuals. (1095)
Back to Our Roots.
A News Report chronicles the latest theories on an original “urmetazoan” from which all multicellular life arose. This ancestor had a “toolkit of genes” which specified four features: body-plan genes, specialized cell types, cells “glued” together, and a communication system.
Raff, Rudolf. The Shape of Life: Genes, Development and the Evolution of Animal Form. Chicago: University of Chicago Press, 1996. An often cited work on the stability and ontogenetic recurrence of bodily plans.
Rainey, Paul and Silvia De Monte. Resolving Conflicts During the Evolutionary Transition to Multicellular Life. Annual Review of Ecology, Evolution, and Systematics. 45/599, 2014. By late 2014, Massey University, Auckland, and Ecole Normale Superieure, Paris, biologists are able to well describe this distinct and persistent advance of life’s unicellular phase within the major transitions scale. Two major themes are its achievement by a mutual balance between each component and the whole organism, i.e. competition and cooperation, along with acquiring a novel degree of individuality. See also Katrin Hammerschmidt, et al (2014) for a similar contribution.
Although the evolution both of eukaryotes and of multicellularity mark major transitions between levels of organization, they are often distinguished on the basis of the nature of the alliance among lower-level entities. Evolution of eukaryotic life from two different and once free-living bacteria counts as an “egalitarian” transition characterized by fairness in reproduction and a mutual coming together of disparate entities. The origin of chromosomes from independently replicating genes marks another egalitarian transition. In contrast, the evolution of multicellular life as well as the evolution of eusocial insect societies are “fraternal” transitions, which originate with an alliance of entities that were most likely identical from the outset and in which a division of labor evolved through epigenetic means. (600).
Ratcliff, William, et al. Experimental Evolution of Multicellularity. Proceedings of the National Academy of Sciences. 109/1595, 2012. University of Minnesota, Evolution and Behavior and BioTechnology Institute, ecologists start their project by situating it within the popular “major transitions” scale and sequence from proteins to people. By this view, life’s emergent passage from eukaryotic cells to cellular assemblies was a natural next stage of “sophisticated, higher-level functionality via cooperation among component cells with complementary behaviors.” See herein concurrent work by Iaroslav Ispolatov, et al, Carl Simpson below, and Cooperative Alliances in the Emergent Individuality section.
Multicellularity was one of the most significant innovations in the history of life, but its initial evolution remains poorly understood. Using experimental evolution, we show that key steps in this transition could have occurred quickly. We subjected the unicellular yeast Saccharomyces cerevisiae to an environment in which we expected multicellularity to be adaptive. We observed the rapid evolution of clustering genotypes that display a novel multicellular life history characterized by reproduction via multicellular propagules, a juvenile phase, and determinate growth. The multicellular clusters are uniclonal, minimizing within-cluster genetic conflicts of interest. Simple among-cell division of labor rapidly evolved. Early multicellular strains were composed of physiologically similar cells, but these subsequently evolved higher rates of programmed cell death (apoptosis), an adaptation that increases propagule production. These results show that key aspects ofmulticellular complexity, a subject of central importance to biology, can readily evolve from unicellular eukaryotes. (Abstract, 1595)