The evolutionary advantage of haploid versus diploid microbe in nutrient-poor environments

Sexual eukaryotic organisms are characterized by haploid and diploid nuclear phases. In many organisms, growth and development occur in both haploid and diploid phases, and there is diversity in the relative length of these phases. To understanding the maintenance of a diversity of life cycles and the advantages of being haploid versus diploid, a number of hypotheses had been put forward. The nutrient-saving hypothesis posits that haploid cells, because they are small, enjoy an advantage in nutrient-poor environments through their higher surface area to volume ratio. In this paper, I present a theoretical examination of this hypothesis and determine the conditions under which it can provide a plausible explanation. Our analysis makes the following predictions. First, the intrinsic population growth rate of the haploid is predicted to be higher than the diploid in nutrient-poor conditions and if the nutrient uptake of microbe saturate and the energy conversion efficiency and the nutrient uptake efficiency are more regulated in the diploid over the haploid. Second, the boundary separating the relative advantage of each ploidy level strongly depends on the relative value of the ploidy-dependent regulation of gene expression (gene dosage effect) and the scaling of mortality with cell size. Third, the effect of differences in nutrient levels has almost nothing with the prediction of nutrient-saving hypothesis for the relative advantage of ploidy levels. Our research represents the importance of the explicit modeling of organisms with process of the life history and population dynamics to understand of evolution of life cycle. And the nutrient limiting hypothesis should be more discussed empirically and the competition experiment should be more done with larger groups other than yeast.