実験進化 : バクテリアの進化生態学の展望
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概要
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Microbial organisms cultured in the laboratory provide a useful tool for analyzing the process of evolution through natural selection. Various mutants arise in a given microbial population, and some of them increase in frequency, replacing previous clones ("periodic selection"). Although there have been a number of studies on changes in the genetic composition of bacterial populations in long-term culture, the ecological mechanisms operating in such replacement during natural selection are less known. This article reviews current knowledge of experimental evolution in the laboratory, focussing particularly on how and why a new mutant replaces previous types. Exploitative competition, interference competition, and predator-mediated (apparent) competition can work as causal mechanisms of replacement, through which an increase of a mutant leads to decreases in the density of previous types. In exploitative competition, a mutant with a higher growth rate and / or lower mortality reduces a resource equilibrium, which, in turn, has a negative effect on the net growth rate of the old types. In interference competition, an increase in a mutant causes a decrease in previous types through direct or indirect inhibition via metabolites. In predator-mediated (apparent) competition, a mutant with a higher growth rate and / or lower predation rate raises the predator equilibrium density, which, in turn, has a negative effect on the net growth rate of the old types. Experimental evidence supports the operation of natural selection through these three negative interactions. However, more experimental studies on the ecological interactions generating evolutionary forces are required for further understanding of evolution through natural selection.
- 日本生態学会の論文