Frequency dependence and cooperation: theory and a test with bacteria
Frequency dependence and cooperation: theory and a test with bacteria
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DOI：
10.1086/519860
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发表时间：
2007-09-01
影响因子：
2.9
通讯作者：
Griffin, Ashleigh S.
中科院分区：
文献类型：
--
作者：
Ross-Gillespie, Adin;Gardner, Andy;Griffin, Ashleigh S.
汉密尔顿的包容性适合度理论为合作问题提供了一个主要的解释。包容适应度理论的一般结论是，除非在限制性条件下，合作不应受制于频率依赖选择。然而，最近对微生物系统的几项研究表明，当作弊者较少时，作弊者（不合作）的相对适合度更大。在这里，我们从理论上证明，当存在(1)足够的种群结构或(2)合作水平与总体种群增长之间存在关联时，这种频率依赖性选择可能发生在微生物中。我们使用致病菌铜绿假单胞菌，在种群结构最小化的条件下，通过不同比例的产生清除铁的铁载体分子（合作者）和不产生铁载体分子（作弊者）的菌株竞争，来检验预测(2)及其潜在假设。我们发现，作弊者的相对适合度和混合培养的生产力都与初始作弊者频率呈显著负相关。此外，当种群生长期实验缩短时，频率依赖强度降低。更一般地说，我们认为合作性状的频率依赖选择可能在微生物中比在后生动物中更常见，因为强选择、结构和合作依赖生长将在微生物种群中更常见。
Hamilton's inclusive fitness theory provides a leading explanation for the problem of cooperation. A general result from inclusive fitness theory is that, except under restrictive conditions, cooperation should not be subject to frequency-dependent selection. However, several recent studies in microbial systems have demonstrated that the relative fitness of cheaters, which do not cooperate, is greater when cheaters are rarer. Here we demonstrate theoretically that such frequency-dependent selection can occur in microbes when there is ( 1) sufficient population structuring or ( 2) an association between the level of cooperation and total population growth. We test prediction ( 2) and its underlying assumption, using the pathogenic bacterium Pseudomonas aeruginosa, by competing strains that produce iron-scavenging siderophore molecules ( cooperators) with nonproducers ( cheaters) at various ratios, under conditions that minimize population structuring. We found that both the relative fitness of cheaters and the productivity of the mixed culture were significantly negatively related to initial cheater frequency. Furthermore, when the period of population growth was experimentally shortened, the strength of frequency dependence was reduced. More generally, we argue that frequency-dependent selection on cooperative traits may be more common in microbes than in metazoans because strong selection, structuring, and cooperation-dependent growth will be more common in microbial populations.