缓慢扩张者通过在微生物菌落中形成凹陷的前沿侵入
Slow expanders invade by forming dented fronts in microbial colonies
摘要：
大多数生物都在太空中生长，无论它们是在宿主组织中传播的病毒还是在新大陆上定居的入侵物种。进化通常在空间增长过程中选择更高的扩张速率，但有人认为，在某些条件下，较慢的扩张者可以接管。在这里，我们报告这样的种群动力学的实验观察。我们证明，速度较慢的突变体获胜时，不仅这两种类型的混合在前面，但也当它们在空间上分离成部门。后者被认为是不可能的，因为以前的研究只集中在扩张速度介导的全球竞争，而忽略了部门边界的局部竞争。我们开发了一个理论的部门几何，占本地和全球竞争，并描述了所有可能的部门形状。特别是，该理论预测，一个速度较慢但更具竞争力的突变体在接管扩张前沿时会形成一个凹陷的V形扇区。这样的扇区确实在实验中被观察到，它们的形状与理论定量吻合。在模拟中，我们进一步探讨了几种机制，可以提供缓慢的扩张与本地的竞争优势，并表明他们都很好地描述了我们的理论。总之，我们的研究结果揭示了以前未探索的空间竞争的结果，并建立了一个通用的框架，以了解不断扩大的人口的进化和生态动态。
英文摘要：
Most organisms grow in space, whether they are viruses spreading within a host tissue or invasive species colonizing a new continent. Evolution typically selects for higher expansion rates during spatial growth, but it has been suggested that slower expanders can take over under certain conditions. Here, we report an experimental observation of such population dynamics. We demonstrate that the slower mutants win not only when the two types are intermixed at the front but also when they are spatially segregated into sectors. The latter was thought to be impossible because previous studies focused exclusively on the global competitions mediated by expansion velocities but overlooked the local competitions at sector boundaries. We developed a theory of sector geometry that accounts for both local and global competitions and describes all possible sector shapes. In particular, the theory predicted that a slower, but more competitive, mutant forms a dented V-shaped sector as it takes over the expansion front. Such sectors were indeed observed experimentally and their shapes matched up quantitatively with the theory. In simulations, we further explored several mechanism that could provide slow expanders with a local competitive advantage and showed that they are all well-described by our theory. Taken together, our results shed light on previously unexplored outcomes of spatial competition and establish a universal framework to understand evolutionary and ecological dynamics in expanding populations.
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