819 research outputs found
Sperm Sociality: Cooperation, Altruism, and Spite
The idea of subfertile or altogether infertile sperm seems an evolutionary paradox, so why have they evolved in a diverse set of species, from molluscs to mice? Understanding sperm sociality may provide the answer
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Sucrose Utilization in Budding Yeast as a Model for the Origin of Undifferentiated Multicellularity
We use the budding yeast, Saccharomyces cerevisiae, to investigate one model for the initial emergence of multicellularity: the formation of multicellular aggregates as a result of incomplete cell separation. We combine simulations with experiments to show how the use of secreted public goods favors the formation of multicellular aggregates. Yeast cells can cooperate by secreting invertase, an enzyme that digests sucrose into monosaccharides, and many wild isolates are multicellular because cell walls remain attached to each other after the cells divide. We manipulate invertase secretion and cell attachment, and show that multicellular clumps have two advantages over single cells: they grow under conditions where single cells cannot and they compete better against cheaters, cells that do not make invertase. We propose that the prior use of public goods led to selection for the incomplete cell separation that first produced multicellularity.Molecular and Cellular Biolog
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Improved Use of a Public Good Selects for the Evolution of Undifferentiated Multicellularity
We do not know how or why multicellularity evolved. We used the budding yeast, Saccharomyces cerevisiae, to ask whether nutrients that must be digested extracellularly select for the evolution of undifferentiated multicellularity. Because yeast use invertase to hydrolyze sucrose extracellularly and import the resulting monosaccharides, single cells cannot grow at low cell and sucrose concentrations. Three engineered strategies overcame this problem: forming multicellular clumps, importing sucrose before hydrolysis, and increasing invertase expression. We evolved populations in low sucrose to ask which strategy they would adopt. Of 12 successful clones, 11 formed multicellular clumps through incomplete cell separation, 10 increased invertase expression, none imported sucrose, and 11 increased hexose transporter expression, a strategy we had not engineered. Identifying causal mutations revealed genes and pathways, which frequently contributed to the evolved phenotype. Our study shows that combining rational design with experimental evolution can help evaluate hypotheses about evolutionary strategies.Molecular and Cellular Biolog
Enforcement is central to the evolution of cooperation.
Cooperation occurs at all levels of life, from genomes, complex cells and multicellular organisms to societies and mutualisms between species. A major question for evolutionary biology is what these diverse systems have in common. Here, we review the full breadth of cooperative systems and find that they frequently rely on enforcement mechanisms that suppress selfish behaviour. We discuss many examples, including the suppression of transposable elements, uniparental inheritance of mitochondria and plastids, anti-cancer mechanisms, reciprocation and punishment in humans and other vertebrates, policing in eusocial insects and partner choice in mutualisms between species. To address a lack of accompanying theory, we develop a series of evolutionary models that show that the enforcement of cooperation is widely predicted. We argue that enforcement is an underappreciated, and often critical, ingredient for cooperation across all scales of biological organization
Reply to: Broad definitions of enforcement are unhelpful for understanding evolutionary mechanisms of cooperation.
Sucrose Utilization in Budding Yeast as a Model for the Origin of Undifferentiated Multicellularity
We use the budding yeast, Saccharomyces cerevisiae, to investigate one model for the initial emergence of multicellularity: the formation of multicellular aggregates as a result of incomplete cell separation. We combine simulations with experiments to show how the use of secreted public goods favors the formation of multicellular aggregates. Yeast cells can cooperate by secreting invertase, an enzyme that digests sucrose into monosaccharides, and many wild isolates are multicellular because cell walls remain attached to each other after the cells divide. We manipulate invertase secretion and cell attachment, and show that multicellular clumps have two advantages over single cells: they grow under conditions where single cells cannot and they compete better against cheaters, cells that do not make invertase. We propose that the prior use of public goods led to selection for the incomplete cell separation that first produced multicellularity
A Quantitative Test of Population Genetics Using Spatio-Genetic Patterns in Bacterial Colonies
It is widely accepted that population genetics theory is the cornerstone of
evolutionary analyses. Empirical tests of the theory, however, are challenging
because of the complex relationships between space, dispersal, and evolution.
Critically, we lack quantitative validation of the spatial models of population
genetics. Here we combine analytics, on and off-lattice simulations, and
experiments with bacteria to perform quantitative tests of the theory. We study
two bacterial species, the gut microbe Escherichia coli and the opportunistic
pathogen Pseudomonas aeruginosa, and show that spatio-genetic patterns in
colony biofilms of both species are accurately described by an extension of the
one-dimensional stepping-stone model. We use one empirical measure, genetic
diversity at the colony periphery, to parameterize our models and show that we
can then accurately predict another key variable: the degree of short-range
cell migration along an edge. Moreover, the model allows us to estimate other
key parameters including effective population size (density) at the expansion
frontier. While our experimental system is a simplification of natural
microbial community, we argue it is a proof of principle that the spatial
models of population genetics can quantitatively capture organismal evolution
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Host control and the evolution of cooperation in host microbiomes.
Humans, and many other species, are host to diverse symbionts. It is often suggested that the mutual benefits of host-microbe relationships can alone explain cooperative evolution. Here, we evaluate this hypothesis with evolutionary modelling. Our model predicts that mutual benefits are insufficient to drive cooperation in systems like the human microbiome, because of competition between symbionts. However, cooperation can emerge if hosts can exert control over symbionts, so long as there are constraints that limit symbiont counter evolution. We test our model with genomic data of two bacterial traits monitored by animal immune systems. In both cases, bacteria have evolved as predicted under host control, tending to lose flagella and maintain butyrate production when host-associated. Moreover, an analysis of bacteria that retain flagella supports the evolution of host control, via toll-like receptor 5, which limits symbiont counter evolution. Our work puts host control mechanisms, including the immune system, at the centre of microbiome evolution
Bacterial defences: mechanisms, evolution and antimicrobial resistance
Throughout their evolutionary history, bacteria have faced diverse threats from other microorganisms, including competing bacteria, bacteriophages and predators. In response to these threats, they have evolved sophisticated defence mechanisms that today also protect bacteria against antibiotics and other therapies. In this Review, we explore the protective strategies of bacteria, including the mechanisms, evolution and clinical implications of these ancient defences. We also review the countermeasures that attackers have evolved to overcome bacterial defences. We argue that understanding how bacteria defend themselves in nature is important for the development of new therapies and for minimizing resistance evolution
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