Most organisms have sensory systems that detect environmental conditions and allow for plastic responses that improve fitness. As the pattern of environmental change itself shifts, it is important to understand how these plastic responses determine population persistence. We studied the response of the yeast Saccharomyces cerevisiae to environmental stress and investigated the population dynamic outcomes. After responding to harsh environments, yeast may require a longer acclimation time (lag time) before they begin to grow exponentially and, thus, have a disadvantage in a directly competitive environment. Yeast cells have two main forms – vegetative and spore – which differ in their abilities to respond quickly to nutrients and to survive stressful conditions. Using five independent natural isolates from different global regions, we held spores and vegetatively growing cells in different adverse conditions and then introduced them into a variety of different rich medias in order to obtain growth curves by repeated measurement of optical densities. Additionally, to observe strain growth in an environment more representative of growth conditions in nature, we obtained growth curves of the same treatments with rich medias supplemented with metabolic or environmental byproducts likely to be present in yeast communities.
Results/Conclusions
Based on preliminary results across the five tested regional strains of S. cerevisiae, vegetative cells had shorter lag periods of growth, including trials in which trauma-induced, relative fragility in vegetative cells was hypothesized. In all trials – ideal control conditions, extreme cold, extreme heat/desiccation, depleted nutrients, harsh solvents, and a chemical digestion treatment (mimicking passing through a fly gut) – vegetative cells prevailed relative to spores of the same strain but with varying strengths across regions of origin. In West African strains, for example, acclimation time variation between vegetative cells and spores was much less significant than that of European strains, about an 8 percent difference compared to a 51 percent difference, respectively. In combination with previously acquired data on the survivorship of vegetative cells and sporulated cells, we predict that generally, despite regional differences, this competitive advantage of cells hesitant to sporulate (commonly vegetative cells in nature) is not sufficient to competitively exclude cells that are likely to cease vegetative growth and sporulate early in an insect-frequented community.