Laboratoire Matière et Systèmes Complexes

Le lundi 9 décembre à 11h30 en 454A

Asymmetric sexual behavior in budding yeast

Alvaro Banderas, postdoc MSC

Sexual asymmetry refers to the evolution of classes of mating cells within a species. Two types of asymmetries can be distinguished in eukaryotes : sexes and mating-types. Sexes are defined for species where mating cells show a binary size distribution (anisogamy), with females being the large and scarce and males the small and abundant. Such bias in gamete abundance is the substrate for sexual selection and the consequent evolution of the specialized sexually-dimorphic structures necessary for asymmetric sexual behavior in higher organisms. Mating-types on the other hand bear no asymmetries in size or abundance (isogamy). According to evolutionary theory, as a consequence they don’t undergo sexual selection and therefore behave identically to each other. Here I use the isogamous mating-system of budding yeast and the tools from quantitative and systems biology to experimentally show that behavioral sexual asymmetry is an ancient trait, older than the evolution of females and males. Our results show that yeast cells adjust their mating effort according to the primary determinants of individual mating success (distance and encounter probability) in a distributed way, with each cell-type responding specifically to each parameter. I discuss both the mechanisms and possible evolutionary pathways leading to basic asymmetric sexual behavior.

Mechanical response of soft cellular systems

François Villemot, postdoc MSC

A cellular material under shear strain will deform elastically until the appearance of the first plastic events. These plastic events change the topology of the material, which is a major parameter for many of its properties, including its elastic moduli. Additionally, the increase in topological disorder created by straining the material is reminiscent of the melting of atomistic solids, which is usually described by the nucleation and propagation of defects. We therefore aim to describe the mechanical response of soft cellular materials with numerical simulations of elemental defects (pairs of edge dislocations) which provide an indirect measurement of the elastic moduli, as well as the core energy of the defects, which is a decisive term governing the melting scenario. We also develop a methodology to properly compute the shear modulus using the Cellular Potts Model, which is not hindered by the inherent anisotropy of the underlying lattice.