Identification of Early Morphological Variation in Novel Multicellular Saccharomyces Cerevisiae Phenotypes
Multicellularity has developed independently many times throughout evolutionary history. While constraints on time and environmental conditions make studying early transitions in the field difficult, the process can be modeled in the lab. When S. cerevisiae is grown under gravitational selection, the pressure for larger cells results in the formation of multicellular individuals. When a novel stressor, such as heat, is applied to the population, the development of distinct multicellular phenotypes occurs. The goal of this work was to identify, isolate, and characterize two of the early multicellular phenotypes that arose during gravitational selection with added heat stress. Two phenotypes were identified; the 'bubble' phenotype, and the 'branch' phenotype. These forms differ in morphology, population growth, and settling ability.
Both the bubble and branch could be successfully isolated from the original cultures, and used to regrow replicate populations. This system allows us to look at early multicellular traits and interactions in a controlled environment, and may aid in our understanding of an early evolutionary transition in response to stress. Further work will involve competition assays to test the isolated phenotypes against each other and the ancestor multicellular strain. Additionally, continued individual characterization will be done, including growth curves and genetic sequencing.