"Ant" and "grasshopper" life-history strategies in Saccharomyces cerevisiae

Abstract

From the evolutionary and ecological points of view, it is essential to distinguish between the genetic and environmental components of the variability of life-history traits and their trade-offs. Among the factors affecting this variability the resource uptake rate deserves particular attention, because it depends on both the environment and the genetic background of the individuals. In order to unravel the bases of the life-history strategies in yeast, we grew a collection of twelve strains of Saccharomyces cerevisiae from different industrial and geographic origins in three culture media differing for their glucose content. Using a population dynamics model to fit the change of population size over time we estimated the intrinsic growth rate (r), the carrying capacity (K), the mean cell size and the glucose consumption rate per cell. The life-history traits, as well as the glucose consumption rate, displayed large genetic and plasic variability and genetic-by-environment interactions. Within each medium growth rate and carrying capacity were not correlated, but a marked tradeoff between these traits was observed over the media, with high K and low r in the glucose rich medium and low K and high r in the other media. The cell size was tigthly negatively correlated to carrying in all conditions. The resource consumpion rate appeared to be a clear-cut determinant of both the carrying capacity and the cell size in all media, since it accounted for 37% to 8496 of the variation of those traits. In a given medium, the strains that consume glucose at high rate have large cell size and low carrying capacity, while the strains the consume glucose at low rate have small cell size but high carrying capacity. These two contrasted behaviours may be metaphorically defined as "ant" and "grasshopper" strategies of resource utilization. Interestingly a strains may be "ant" in one medium and "grasshopper" in another. These life-history strategies are discussed with regards to yeast physiology, and in evolutionary perspective. © 2008 Spor et al.