Goldschmidt Felix, Regoes Roland R, Johnson David R
Department of Environmental Systems Science, ETH Zürich, Zürich, Switzerland.
Department of Environmental Microbiology, Eawag, Dübendorf, Switzerland.
ISME J. 2017 Sep;11(9):2112-2123. doi: 10.1038/ismej.2017.76. Epub 2017 May 23.
Successive range expansions occur within all domains of life, where one population expands first (primary expansion) and one or more secondary populations then follow (secondary expansion). In general, genetic drift reduces diversity during range expansion. However, it is not clear whether the same effect applies during successive range expansion, mainly because the secondary population must expand into space occupied by the primary population. Here we used an experimental microbial model system to show that, in contrast to primary range expansion, successive range expansion promotes local population diversity. Because of mechanical constraints imposed by the presence of the primary population, the secondary population forms fractal-like dendritic structures. This divides the advancing secondary population into many small sub-populations and promotes intermixing between the primary and secondary populations. We further developed a mathematical model to simulate the formation of dendritic structures in the secondary population during succession. By introducing mutations in the primary or dendritic secondary populations, we found that mutations are more likely to accumulate in the dendritic secondary populations. Our results thus show that successive range expansion can promote intermixing over the short term and increase genetic diversity over the long term. Our results therefore have potentially important implications for predicting the ecological processes and evolutionary trajectories of microbial communities.
连续的范围扩张发生在生命的所有领域，其中一个种群首先扩张（初级扩张），然后一个或多个次级种群随后跟进（次级扩张）。一般来说，遗传漂变会在范围扩张期间降低多样性。然而，尚不清楚在连续的范围扩张期间是否会产生同样的影响，主要是因为次级种群必须扩张到初级种群占据的空间中。在这里，我们使用了一个实验性微生物模型系统来表明，与初级范围扩张相反，连续的范围扩张促进了局部种群的多样性。由于初级种群的存在所施加的机械限制，次级种群形成了分形状的树枝状结构。这将前进的次级种群分成许多小的亚种群，并促进了初级和次级种群之间的混合。我们进一步开发了一个数学模型来模拟连续过程中次级种群中树枝状结构的形成。通过在初级或树枝状次级种群中引入突变，我们发现突变更有可能在树枝状次级种群中积累。因此，我们的结果表明，连续的范围扩张可以在短期内促进混合，并在长期内增加遗传多样性。因此，我们的结果对于预测微生物群落的生态过程和进化轨迹具有潜在的重要意义。
