Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697-2525, USA.
Philos Trans R Soc Lond B Biol Sci. 2010 Aug 27;365(1552):2515-22. doi: 10.1098/rstb.2010.0003.
Microbial secretions manipulate the environment and communicate information to neighbours. The secretions of an individual microbe typically act externally and benefit all members of the local group. Secreting imposes a cost in terms of growth, so that cheaters that do not secrete gain by sharing the benefits without paying the costs. Cheaters have been observed in several experimental and natural settings. Given that cheaters grow faster than secretors when in direct competition, what maintains the widely observed patterns of secretion? Recent theory has emphasized the genetic structure of populations, in which secretors tend to associate spatially with other secretors, reducing direct competition and allowing highly secreting groups to share mutual benefits. Such kin selection can be a powerful force favouring cooperative traits. Here, I argue that, although kin selection is a factor, the combination of mutation and demographic processes dominate in determining the relative fitness of secretors versus cheaters when measured over the full cycle of microbial life history. Key demographic factors include the local density of microbes at which secretion significantly alters the environment, the extent to which secretion enhances microbial growth and maximum local density, and the ways in which secretion alters colony survival and dispersal.
微生物分泌物可以操纵环境并与周围的微生物进行信息交流。个体微生物的分泌物通常作用于外部，使局部群体中的所有成员受益。分泌会带来生长成本，因此不分泌的作弊者可以通过分享利益而不承担成本来获益。在多个实验和自然环境中都观察到了作弊者。鉴于作弊者在直接竞争中比分泌者生长得更快，那么是什么维持了广泛观察到的分泌模式呢？最近的理论强调了种群的遗传结构，在这种结构中，分泌者倾向于在空间上与其他分泌者联系在一起，从而减少直接竞争，并允许高度分泌的群体共享互惠互利。这种亲缘选择可以成为促进合作特征的强大力量。在这里，我认为，尽管亲缘选择是一个因素，但在衡量微生物整个生命史周期的相对适应度时，突变和人口过程的组合在决定分泌者与作弊者之间的相对适应度方面占主导地位。关键的人口因素包括微生物的局部密度，在这个密度下，分泌会显著改变环境，以及分泌对微生物生长和最大局部密度的增强程度，以及分泌改变菌落存活和扩散的方式。
