Department of Biomedical Engineering, Duke University, Durham, NC 27708.
Proc Natl Acad Sci U S A. 2014 Feb 4;111(5):1969-74. doi: 10.1073/pnas.1315954111. Epub 2014 Jan 21.
Dispersal is necessary for spread into new habitats, but it has also been shown to inhibit spread. Theoretical studies have suggested that the presence of a strong Allee effect may account for these counterintuitive observations. Experimental demonstration of this notion is lacking due to the difficulty in quantitative analysis of such phenomena in a natural setting. We engineered Escherichia coli to exhibit a strong Allee effect and examined how the Allee effect would affect the spread of the engineered bacteria. We showed that the Allee effect led to a biphasic dependence of bacterial spread on the dispersal rate: spread is promoted for intermediate dispersal rates but inhibited at low or high dispersal rates. The shape of this dependence is contingent upon the initial density of the source population. Moreover, the Allee effect led to a tradeoff between effectiveness of population spread and survival: increasing the number of target patches during dispersal allows more effective spread, but it simultaneously increases the risk of failing to invade or of going extinct. We also observed that total population growth is transiently maximized at an intermediate number of target patches. Finally, we demonstrate that fluctuations in cell growth may contribute to the paradoxical relationship between dispersal and spread. Our results provide direct experimental evidence that the Allee effect can explain the apparently paradoxical effects of dispersal on spread and have implications for guiding the spread of cooperative organisms.
扩散对于进入新栖息地是必要的，但它也被证明会抑制扩散。理论研究表明，强阿利效应的存在可能解释了这些违反直觉的观察结果。由于在自然环境中对这种现象进行定量分析的难度，因此缺乏对这一概念的实验验证。我们通过工程化改造大肠杆菌使其表现出强阿利效应，并研究了阿利效应如何影响工程菌的传播。我们发现，阿利效应导致细菌传播对扩散率的依赖呈双相：在中等扩散率下促进传播，但在低或高扩散率下抑制传播。这种依赖性的形状取决于源种群的初始密度。此外，阿利效应导致种群传播的有效性和生存之间存在权衡：在扩散过程中增加目标斑块的数量可以使传播更有效，但同时也增加了无法入侵或灭绝的风险。我们还观察到，在目标斑块数量中等时，总种群增长会暂时最大化。最后，我们证明细胞生长的波动可能促成了扩散与传播之间的矛盾关系。我们的研究结果提供了直接的实验证据，表明阿利效应可以解释扩散对传播的明显矛盾作用，并为指导合作生物的传播提供了启示。
