Développement et unicellularité


Conference Development and Unicellularity

June 5, 2014



Université Paris-Sorbonne, Maison de la Recherche

28 rue Serpente

75006 Paris

Salle de conférence (D035)


Avec le soutien de la chaire IUF junior de Thomas Pradeu


Colloque organisé par Karine Prévot (Université Paris Ouest Nanterre-La Défense)

et Thomas Pradeu (Université Paris Sorbonne, IUF)



Program and abstracts:


Note: Please contact me if you are interested in the PDFs of this conference (some of them are available below, others are simply too big for this webpage)


1. Unicellular organisms as models of development


10h-11h: Karine Prévot (Université Paris Ouest Nanterre) Introduction: conceptualizing development at the level of microbiology (PDF).

Abstract: Research on development focused on multicellular model organisms that were supposed to represent all the metazoans. Recent studies on both model organisms and developmental processes such as developmental symbiosis show that unicellular organisms (microbes) can also be exploited as models to study development. In this presentation I will discuss the relevance of microbiology as a level at which development can be examined, and the consequences of this on the definition of the individuals that develop.


11h-11h30: break


11h30-12h30: Michael Travisano (University of Minnesota): Experimental evolution of multicellularity (Part 1 of the talk available as a PDF; please contact me if you want the rest of the PDF)

Abstract: The evolution of multicellularity dramatically changed life on earth, leading to vast changes in the complexity of life. Virtually all life that we can see without magnification is multicellular, and contains from tens to trillions of cells. Investigating the evolutionary origins of multicellularity helps to understand the complexity of life, but is difficult, because multicellularity in nature evolved millions of years ago. To overcome this limitation, we've experimentally evolved multicellularity in the laboratory, starting with the single celled Baker's yeast. Using selection for fast settling in liquid, we show that multicellular yeast readily evolve from their single celled ancestor in as little as 7 days. The multicellular yeast grow by persistent attachment of daughter cells to mother cells, producing a characteristic -snowflake- body plan. These snowflake yeast evolve complex life-histories including juvenile and adult life stages, and respond to selection to body size. They also evolve a form of terminal cellular differentiation that promotes rapid growth. We've continued settling selection for over 7 months, and see that the multicellular yeast continue to increase in settling rate, and did so in three ways. First they increase in the number of cells as we initially observed, then they also increase the size of cells, and finally they evolve a more hydrodynamic shape. The first two multicellular adaptations make multicellular yeast bigger and thus faster settling. But larger size carries a cost: slower growth rates. The last adaptation, more hydrodynamic shape, allows for faster settling without imposing a growth rate cost. This suggests that the costs of increased size, which have been seen in algae and bacteria, may drive the evolution of increased complexity by favoring innovation.


(The most important thing in this image is the little grey dot)


12h30-14h30: lunch



2. Organisms at the frontier between unicellularity and multicellularity


14h30-15h30: Audrey Dussutour (CNRS): Behavioral phenotypes and complex intercellular interactions in the true slime mold (please contact me for the whole PDF)

Abstract: Research on animals has frequently made the assumption that all individuals within a species express the same tendencies. However, in the past decade, it has been demonstrated that even slight differences in the tendency of individual animals to display a given behavior may have consequences for the ecology and evolution of populations. Examples of individual differences are found for a large number of behavioral tendencies, including boldness, aggressiveness, fearfulness, responsiveness to environmental stimuli, etc. Recent advances in our understanding of the evolution of sociality have also come from systems that express pronounced individual differences in traits such as social responsiveness and cooperativeness. Behavioral differences are a widespread phenomenon throughout the animal kingdom, fish, birds, reptiles, amphibians, arthropods, and mollusks. Surprisingly little attention has been paid to the behavioral differences that might exist in unicellular organisms. In this presentation, I will strive to fill this gap by demonstrating the complexities inherent in the behavioural responses of the acellular slime mold Physarum polycephalum to environmental and social cues.

Slime mold_Dussutour


15h30-16h: break


16h-17h: Darja Dubravcic: Not everybody is social in social amoeba (PDF).

Abstract: The social amoeba Dictyostelium discoideum is widely known for its cooperative behavior. Upon starvation, millions of cells aggregate and form a fruiting body that allows better dispersion of dormant spores. But not all cells aggregate and take part in this social act. A part of the population ignores the aggregation signal and continues behaving as single cells. We have developed a new cell tracking technique that enabled us to quantify population partitioning into social/aggregating and unsocial/non-aggregating cells. During my talk I will discuss genetic and phenotypic mechanisms that affect the cell fate, fitness costs and benefits of both strategies, and evolutionary significance of population partitioning.



17h-17h30 : General discussion