Morgan A D, Buckling A
Department of Zoology, University of Oxford, Oxford, UK.
J Evol Biol. 2006 Nov;19(6):1956-63. doi: 10.1111/j.1420-9101.2006.01148.x.
A potential consequence of host-parasite coevolution in spatially structured populations is parasite local adaptation: local parasites perform better than foreign parasites on their local host populations. It has been suggested that the generally shorter generation times of parasites compared with their hosts contributes to parasites, rather than hosts, being locally adapted. We tested the hypothesis that relative generation times of hosts and parasites affect local adaptation of hosts and parasites, using the bacterium Pseudomonas fluorescens and a lytic phage as host and parasite, respectively. Generation times were not directly manipulated, but instead one of the coevolving partners was regularly removed and replaced with a population from an earlier time point. Thus, one partner underwent more generations than the other. Manipulations were carried out at both early and later periods of coevolutionary interactions. At early stages of coevolution, host and parasites that underwent relatively more generations displayed higher levels of resistance and infectivity, respectively. However, the relative number of generations that bacteria and phages underwent did not change the level of local adaptation relative to control populations. This is likely because generalist hosts and parasites are favoured during early stages of coevolution, preventing local adaptation. By contrast, at later stages manipulations had no effect on either average levels of resistance or infectivity, or alter the level of local adaptation relative to the controls, possibly because traits other than resistance and infectivity were under strong selection. Taken together, these data suggest that the relative generation times of hosts and parasites may not be an important determinant of local adaptation in this system.
在空间结构化种群中，宿主 - 寄生虫协同进化的一个潜在后果是寄生虫的局部适应性：本地寄生虫在其本地宿主种群上的表现优于外来寄生虫。有人提出，与宿主相比，寄生虫通常较短的世代时间有助于寄生虫而非宿主实现局部适应。我们以荧光假单胞菌和一种裂解性噬菌体分别作为宿主和寄生虫，检验了宿主和寄生虫的相对世代时间会影响宿主和寄生虫局部适应的假说。世代时间并未直接操控，而是定期移除一个协同进化的伙伴并用来自更早时间点的种群取而代之。因此，一个伙伴经历的世代比另一个更多。在协同进化相互作用的早期和后期都进行了操控。在协同进化的早期阶段，经历相对更多世代的宿主和寄生虫分别表现出更高水平的抗性和感染性。然而，细菌和噬菌体经历的相对世代数相对于对照种群并未改变局部适应水平。这可能是因为在协同进化的早期阶段，泛化的宿主和寄生虫更受青睐，从而阻止了局部适应。相比之下，在后期阶段，操控对平均抗性或感染性水平均无影响，也未改变相对于对照的局部适应水平，这可能是因为除抗性和感染性之外的其他性状受到了强烈选择。综上所述，这些数据表明，宿主和寄生虫的相对世代时间可能不是该系统中局部适应的重要决定因素。
