title: The evolutionary advantage of haploid versus diploid microbes in nutrient-poor environments.
abstract: 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 the relative length of these phases exhibits considerable diversity. A number of hypotheses have been put forward to explain the maintenance of this diversity of life cycles and the advantage of being haploid versus that of being diploid. The nutrient-limitation hypothesis postulates that haploid cells, because they are small and thus have a higher surface area to volume ratio, are advantageous in nutrient-poor environments. In this paper, we examine this hypothesis theoretically and determine the conditions under which it holds. On the basis of our analysis, we make the following predictions. First, the relative advantages of different ploidy levels strongly depend on the ploidy-dependent energy conversion efficiency and the scaling of mortality with cell size. Specifically, haploids enjoy a higher intrinsic population growth rate than diploids do under nutrient-poor conditions, but under nutrient-rich conditions the intrinsic population growth rate of diploids is higher, provided that the energy conversion efficiency of diploids is higher than that of haploids and the scaling of mortality with cell size is weak. Second, differences in nutrient concentration in the inflowing medium have almost no effect on the relative advantage of ploidy levels at population equilibrium. Our study illustrates the importance of explicit modeling of microbial life history and population dynamics to understand the evolution of ploidy levels.
authors.affiliation: Department of Zoology, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada. Electronic address: bessho@zoology.ubc.ca.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Bessho
authors.affiliation: Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan. Electronic address: yohiwasa@kyudai.jp.
authors.forename: Yoh
authors.initials: Y
authors.lastname: Iwasa
authors.affiliation: Department of Mathematics and Statistics, Queen׳s University, Kingston, ON K7L 3N6, Canada. Electronic address: tday@mast.queensu.ca.
authors.forename: Troy
authors.initials: T
authors.lastname: Day
mesh_terms: D005075:Biological Evolution; D004171:Diploidy; D005502:Food; D006238:Haploidy; D008954:Models, Biological; D011156:Population Density; D011157:Population Dynamics; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development
keywords: Allometry; Mathematical model; Microbe life history model; Ploidy evolution; Population dynamics