Tue, 08 Dec | Zoom Webinar

On the evolution of collective properties in nested Darwinian populations.

Keynote by Silvia De Monte, with talks on "Evolution of multicellularity by collective integration of spatial information" by Renske Vroomans and on "Eco-evolutionary dynamics from the RNA world to microbes: novelty as a byproduct of self-organisation" by Enrico Sandro Colizzi.
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On the evolution of collective properties in nested Darwinian populations.

Time & Location

08 Dec 2020, 14:00 – 16:00 CET
Zoom Webinar

About the Event

The  extent to which natural communities can be seen as 'superorganisms'  whose collective properties can be directly selected is unclear. Methods of high-throughput screening and selection of microbial communities  have recently raised the possibility of exerting artificial selection so  as to obtain desirable community-level properties. In this talk, I will  address the question of how a target collective phenotype comes to be  reinforced in the course of evolution by successive changes in the  traits of the composing units. I will use a simple two-species model to  illustrate the effects of selection for community composition on  community ecology. In this model, communities are periodically assessed  for their properties and a new generation of collectives is generated by  dilution of the best performing ones. In particular, I will discuss the  role of the collective generation time scale and bottleneck size in  facilitating the emergence, through the adjustment of species  interactions, of an evolutionarily stable composition. As in  developmental processes, the achievement of the optimal composition is  realized by 'ecological canalization', which buffers against initial  fluctuations in newborn community composition. Finally, I will discuss  some ongoing efforts for understanding what emergent properties of more  complex communities can be more efficiently acted upon by natural  selection. - Silvia De Monte, Ecole Nationale Supérieure, Paris, France

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The evolution of multicellularity is a major transition in individuality. At the onset of this transition, interactions between cells in a group generated novel properties at the aggregate level, which in turn determined the selection pressures experienced by these cells. We study the transition to multicellularity with an evolutionary model in which cells can mutate the strength of their adhesion to others upon division. In order to divide, they have to locate resources by navigating a shallow, noisy gradient with chemotaxis. The location of these resources changes periodically, and a cell's fitness depends only on its proximity to the resources at the end of a season. We find that multicellular aggregates locate resources through emergent collective chemotaxis more efficiently than single cells;  this emergent property enables evolution of adhesion. When the resources move too frequently however, selection favours dispersal and cells remain unicellular. Furthermore, the spatial population dynamics resulting from one strategy hinder the invasion of the other strategy through interference competition, creating a regime of evolutionary bi-stability. We conclude that collective behaviour can drive the evolution of undifferentiated multicellularity. - Renske Vroomans, Origins Center, The Netherlands

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Throughout 4 billion years of history, evolution has generated novel traits, forms and functions. Novelty often arises from re-purposing old features in a new context: bird feathers originally evolved for thermo-regulation in dinosaurs, the optical properties of the eye are generated by over-expression of common homeostatic proteins, and life itself originated as a side effect of an evolving prebiotic chemistry. In all these cases, the collective eco-evolutionary dynamics of interacting individuals generate a new level of organisation - a collective phenotype. This provides a novel context in which functions can emerge that do not exist at the level of individuals. To study how novelty comes about, I built two models inspired by the RNA world (a hypothetical evolutionary stage that preceded cellular life). In these models, RNA molecules replicate one another, and self-organise into higher-level structures that behave as Darwinian units themselves. RNAs acquire novel functions in the context of these structures. In the first of the two models, I show that molecular parasites behave effectively like mutualists. In the second, a germline-soma division of labour evolves, where soma-like terminal differentiation arises through mutations. In both models, these functions are novel because we do not pre-define them. Therefore, a theory for the evolution of novelty only requires that higher levels of organisation can emerge from local interactions of evolving individuals. I will then show how both these results translate to microbial eco-evolutionary dynamics. - Enrico Sandro Colizzi, Origins Center, Leiden University, The Netherlands

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