文章基本信息

标题：Crowded growth leads to the spontaneous evolution of semistable coexistence in laboratory yeast populations
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作者：Evgeni M. Frenkel ; Michael J. McDonald ; J. David Van Dyken 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：36
页码：11306-11311
DOI：10.1073/pnas.1506184112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceThe spontaneous emergence of stable coexistence between competing lineages in experimental evolution illustrates principles behind the creation and maintenance of biodiversity. Here, we present the first experimental observation of a general mechanism that leads to stable diversification in microbial populations despite competition for shared resources. Coexistence in our system depends on a tradeoff between growth and the ability to avoid cellular crowding. We elucidate the biophysical and genetic basis of this coexistence, and introduce a mathematical model that explains our results. Our analysis demonstrates that this coexistence can be perturbed by evolution on longer time scales, providing a unique quantitative example of how the interactions between ecological and evolutionary processes can create and destroy diversity in microbial populations. Identifying the mechanisms that create and maintain biodiversity is a central challenge in biology. Stable diversification of microbial populations often requires the evolution of differences in resource utilization. Alternatively, coexistence can be maintained by specialization to exploit spatial heterogeneity in the environment. Here, we report spontaneous diversification maintained by a related but distinct mechanism: crowding avoidance. During experimental evolution of laboratory Saccharomyces cerevisiae populations, we observed the repeated appearance of "adherent" (A) lineages able to grow as a dispersed film, in contrast to their crowded "bottom-dweller" (B) ancestors. These two types stably coexist because dispersal reduces interference competition for nutrients among kin, at the cost of a slower maximum growth rate. This tradeoff causes the frequencies of the two types to oscillate around equilibrium over the course of repeated cycles of growth, crowding, and dispersal. However, further coevolution of the A and B types can perturb and eventually destroy their coexistence over longer time scales. We introduce a simple mathematical model of this "semistable" coexistence, which explains the interplay between ecological and evolutionary dynamics. Because crowded growth generally limits nutrient access in biofilms, the mechanism we report here may be broadly important in maintaining diversity in these natural environments.
关键词：experimental evolution ; coexistence ; fungal adherence ; crowding