Local maladaptation in the anther-smut fungus Microbotryum violaceum to its host plant Silene latifolia:: Evidence from a cross-inoculation experiment
Local maladaptation in the anther-smut fungus Microbotryum violaceum to its host plant Silene latifolia:: Evidence from a cross-inoculation experiment
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DOI：
10.2307/2640776
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发表时间：
1999-04-01
期刊：
影响因子：
3.3
通讯作者：
Shykoff, JA
中科院分区：
文献类型：
--
作者：
Kaltz, O;Gandon, S;Shykoff, JA
传统观点认为，寄生虫比它们的宿主进化得更快，因此更能适应当地环境，也就是说，它们更善于利用同域宿主而不是异域宿主。我们研究了昆虫传播的真菌病原菌堇菜微病菌及其寄主植物银叶的局部适应性。对来自一个元种群的14个自然种群的同域（本地）和异域（外来）病原体和宿主组合进行了感染成功试验。将来自每个种群的最多10个种子科的幼苗分别暴露于来自同一种群、近种群（距离小于10公里）、中间种群（距离小于30公里）和远种群（距离小于170公里）的4种真菌菌株的孢子悬浮液中。我们在真菌种群和品系水平上获得了显著的病原菌X植物侵染成功率（患病植物比例）的相互作用。该病原菌局部适应不良的总体模式是：同域寄主的平均真菌侵染成功率（患病植株的平均比例= 0.32 +/- 0.03 SE）显著低于异域寄主（0.40 +/- 0.02 SE）。14个真菌种群中有5个在同域寄主上的感染成功率没有明显下降，有3个甚至在同域寄主上表现得更好。这种模式与预测寄主-寄生虫系统局部适应模式平均出现的滞后周期模型是一致的。有几个因素可能限制这种病原体相对于其宿主的进化潜力。首先，一个以自交为主的繁殖系统可能通过性重组限制其产生新的毒力类型的能力，而专性异交的寄主S. latifolia可能通过随机交配从抗性等位基因的重排中获益。其次，种群中通常只有少数受感染的个体，因此毒力变异可能通过漂变进一步减少。第三，寄主植物种群之间的迁移率远高于病原体种群之间的迁移率，这可能是因为传粉者更喜欢健康的植物而不是患病的植物。因此，在部分隔离的种群之间的迁移可能更经常地引入新的宿主植物抗性变异，而不是新的寄生虫毒力变异。传染病的地理分布模式支持了移民对这一系统的共同进化动力的贡献。在宿主-病原体种群距离的前10公里范围内，感染成功率增加，这可能是基因交换的自然范围。
Conventional wisdom holds that parasites evolve more rapidly than their hosts and are therefore locally adapted, that is, better at exploiting sympatric than allopatric hosts. We studied local adaptation in the insect-transmitted fungal pathogen Microbotryum violaceum and its host plant Silene latifolia. Infection success was tested in sympatric (local) and allopatric (foreign) combinations of pathogen and host from 14 natural populations from a metapopulation. Seedlings from, up to 10 seed families from each population were exposed to sporidial suspensions from each of four fungal strains derived from the same population, from a near-by population (< 10 km distance), and from two populations at an intermediate (< 30 km) and remote (< 170 km) distance, respectively. We obtained significant pathogen X plant interactions in infection success (proportion of diseased plants) at both fungal population and strain level. There was an overall pattern of local maladaptation of this pathogen: average fungal infection success was significantly lower on sympatric hosts (mean proportion of diseased plants = 0.32 +/- 0.03 SE) than on allopatric hosts (0.40 +/- 0.02). Five of the 14 fungal populations showed no strong reduction in infection success on sympatric hosts, and three even tended to perform better on sympatric hosts. This pattern is consistent with models of time-lagged cycles predicting patterns of local adaptation in host-parasite systems to emerge only on average. Several factors may restrict the evolutionary potential of this pathogen relative to that of its host. First, a predominantly selfing breeding system may limit its ability to generate new virulence types by sexual recombination, whereas the obligately outcrossing host S. latifolia may profit from rearrangement of resistance alleles by random mating. Second, populations often harbor only a few infected individuals, so virulence variation may be further reduced by drift. Third, migration rates among host plant populations are much higher than among pathogen populations, possibly because pollinators prefer healthy over diseased plants. Migration among partly isolated populations may therefore introduce novel host plant resistance variants more often than novel parasite virulence variants. That migration contributes to the coevolutionary dynamics in this system is supported by the geographic pattern of infectivity. Infection success increased over the first 10-km range of host-pathogen population distances, which is likely the natural range of gene exchange.