REVERSE EVOLUTION: SELECTION AGAINST COSTLY RESISTANCE IN DISEASE-FREE MICROCOSM POPULATIONS OF PARAMECIUM CAUDATUM
REVERSE EVOLUTION: SELECTION AGAINST COSTLY RESISTANCE IN DISEASE-FREE MICROCOSM POPULATIONS OF PARAMECIUM CAUDATUM
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DOI：
10.1111/j.1558-5646.2011.01388.x
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发表时间：
2011-12-01
期刊：
影响因子：
3.3
通讯作者：
Kaltz, Oliver
中科院分区：
文献类型：
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作者：
Duncan, Alison B.;Fellous, Simon;Kaltz, Oliver
如果在没有寄生虫的情况下，赋予抗性的基因降低了适应性，那么寄生虫抗性的进化代价就会出现。因此，寄生虫介导的选择可能导致抗性增强和相关的适应性降低，而放松的寄生虫介导的选择可能导致适应性增强和相关的抗性降低的逆向进化。我们在原始动物尾尾草履虫和寄生细菌波状全息孢子虫的实验种群中测试了这一想法。8年后，比较了(1)感染人群、(2)未感染初始人群和(3)先前感染、无寄生虫恢复人群的草履虫对感染和无性繁殖的抵抗力。感染人群中的草履虫抗性更强（+12%），但繁殖率较低（15%），这表明了抗性和适应性之间的进化权衡。恢复种群表现出与原始种群相似的繁殖；然而，最近（3年）恢复种群的抗性与初始种群一样敏感。这表明在抵抗力和适应性之间存在一种弱的、凸的权衡，允许在不完全丧失抵抗力的情况下恢复适应性，有利于维持中间适应性和抵抗力的通才策略。我们的研究结果表明，与寄生虫共同进化可以在无病种群中留下遗传印记。
Evolutionary costs of parasite resistance arise if genes conferring resistance reduce fitness in the absence of parasites. Thus, parasite-mediated selection may lead to increased resistance and a correlated decrease in fitness, whereas relaxed parasite-mediated selection may lead to reverse evolution of increased fitness and a correlated decrease in resistance. We tested this idea in experimental populations of the protozoan Paramecium caudatum and the parasitic bacterium Holospora undulata. After eight years, resistance to infection and asexual reproduction were compared among paramecia from (1) infected populations, (2) uninfected naive populations, and (3) previously infected, parasite-free recovered populations. Paramecia from infected populations were more resistant (+12%), but had lower reproduction (15%) than naive paramecia, indicating an evolutionary trade-off between resistance and fitness. Recovered populations showed similar reproduction to naive populations; however, resistance of recently (3 years) recovered populations were as susceptible as naive populations. This suggests a weak, convex trade-off between resistance and fitness, allowing recovery of fitness, without complete loss of resistance, favoring the maintenance of a generalist strategy of intermediate fitness and resistance. Our results indicate that (co)evolution with parasites can leave a genetic signature in disease-free populations.