在自然界，表现型之间的随机切换（“风险对冲”）是生物在变幻无常的环境中求生存的常见现象。对暴露于一个与脊椎动物免疫系统等环境有相似性的波动体系中的“荧光假单孢菌”所做的一项研究，实时显示了这种行为何以能够发生。
本期封面所示为一个“荧光假单孢菌”菌种的菌落，这个菌种已形成了在不同菌落类型之间随机切换的能力。这种“风险对冲”策略使它们能够在一个不断变化、以对不同菌落有利的人工环境中存活。“风险对冲”在实验室中的形成以及其中所涉及突变的识别，反映了动态环境是怎样推动这种“风险对冲”行为之形成的。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 462, 90-93 (5 November 2009) | doi:10.1038/nature08504
Experimental evolution of bet hedging
Hubertus J. E. Beaumont1,2,3, Jenna Gallie1, Christian Kost1,3, Gayle C. Ferguson1 & Paul B. Rainey1
1 New Zealand Institute for Advanced Study and Allan Wilson Centre for Molecular Ecology & Evolution, Massey University, Private Bag 102904, North Shore Mail Centre, North Shore City 0745, Auckland, New Zealand
2 Institute of Biology Leiden, Leiden University, PO Box 9505, 2300 RA Leiden, The Netherlands
3 Present addresses: Institute of Biology Leiden, Leiden University, PO Box 9505, 2300 RA Leiden, The Netherlands (H.J.E.B.); Department of Bioorganic Chemistry, Max Planck Institute for Chemical Ecology, 07745 Jena, Germany (C.K.).
Correspondence to: Hubertus J. E. Beaumont1,2,3 Correspondence and requests for materials should be addressed to H.J.E.B.
Bet hedging—stochastic switching between phenotypic states1, 2, 3—is a canonical example of an evolutionary adaptation that facilitates persistence in the face of fluctuating environmental conditions. Although bet hedging is found in organisms ranging from bacteria to humans4, 5, 6, 7, 8, 9, 10, direct evidence for an adaptive origin of this behaviour is lacking11. Here we report the de novo evolution of bet hedging in experimental bacterial populations. Bacteria were subjected to an environment that continually favoured new phenotypic states. Initially, our regime drove the successive evolution of novel phenotypes by mutation and selection; however, in two (of 12) replicates this trend was broken by the evolution of bet-hedging genotypes that persisted because of rapid stochastic phenotype switching. Genome re-sequencing of one of these switching types revealed nine mutations that distinguished it from the ancestor. The final mutation was both necessary and sufficient for rapid phenotype switching; nonetheless, the evolution of bet hedging was contingent upon earlier mutations that altered the relative fitness effect of the final mutation. These findings capture the adaptive evolution of bet hedging in the simplest of organisms, and suggest that risk-spreading strategies may have been among the earliest evolutionary solutions to life in fluctuating environments.
