PDF(Pubmed)
Abstract：
BACKGROUND: Adaptation to a stressor can lead to costs on other traits. These costs play an unavoidable role on fitness and influence the evolutionary trajectory of a population. Host defense seems highly subject to these costs, possibly because its maintenance is energetically costly but essential to the survival. When assessing the ecological risk related to pollution, it is therefore relevant to consider these costs to evaluate the evolutionary consequences of stressors on populations. However, to the best of our knowledge, the effects of evolution in irradiate environment on host defense have never been studied. Using an experimental evolution approach, we analyzed fitness across 20 transfers (about 20 generations) in Caenorhabditis elegans populations exposed to 0, 1.4, and 50.0 mGy.h- 1 of 137Cs gamma radiation. Then, populations from transfer 17 were placed in the same environmental conditions without irradiation (i.e., common garden) for about 10 generations before being exposed to the bacterial parasite Serratia marcescens and their survival was estimated to study host defense. Finally, we studied the presence of an evolutionary trade-off between fitness of irradiated populations and host defense.
RESULTS: We found a lower fitness in both irradiated treatments compared to the control ones, but fitness increased over time in the 50.0 mGy.h- 1, suggesting a local adaptation of the populations. Then, the survival rate of C. elegans to S. marcescens was lower for common garden populations that had previously evolved under both irradiation treatments, indicating that evolution in gamma-irradiated environment had a cost on host defense of C. elegans. Furthermore, we showed a trade-off between standardized fitness at the end of the multigenerational experiment and survival of C. elegans to S. marcescens in the control treatment, but a positive correlation between the two traits for the two irradiated treatments. These results indicate that among irradiated populations, those most sensitive to ionizing radiation are also the most susceptible to the pathogen. On the other hand, other irradiated populations appear to have evolved cross-resistance to both stress factors.
CONCLUSIONS: Our study shows that adaptation to an environmental stressor can be associated with an evolutionary cost when a new stressor appears, even several generations after the end of the first stressor. Among irradiated populations, we observed an evolution of resistance to ionizing radiation, which also appeared to provide an advantage against the pathogen. On the other hand, some of the irradiated populations seemed to accumulate sensitivities to stressors. This work provides a new argument to show the importance of considering evolutionary changes in ecotoxicology and for ecological risk assessment.
RESULTS: We found a lower fitness in both irradiated treatments compared to the control ones, but fitness increased over time in the 50.0 mGy.h- 1, suggesting a local adaptation of the populations. Then, the survival rate of C. elegans to S. marcescens was lower for common garden populations that had previously evolved under both irradiation treatments, indicating that evolution in gamma-irradiated environment had a cost on host defense of C. elegans. Furthermore, we showed a trade-off between standardized fitness at the end of the multigenerational experiment and survival of C. elegans to S. marcescens in the control treatment, but a positive correlation between the two traits for the two irradiated treatments. These results indicate that among irradiated populations, those most sensitive to ionizing radiation are also the most susceptible to the pathogen. On the other hand, other irradiated populations appear to have evolved cross-resistance to both stress factors.
CONCLUSIONS: Our study shows that adaptation to an environmental stressor can be associated with an evolutionary cost when a new stressor appears, even several generations after the end of the first stressor. Among irradiated populations, we observed an evolution of resistance to ionizing radiation, which also appeared to provide an advantage against the pathogen. On the other hand, some of the irradiated populations seemed to accumulate sensitivities to stressors. This work provides a new argument to show the importance of considering evolutionary changes in ecotoxicology and for ecological risk assessment.
摘要：
背景：对压力源的适应会导致其他性状的成本。这些成本对健康起着不可避免的作用，并影响种群的进化轨迹。主机防御似乎高度受制于这些成本，可能是因为它的维护成本高昂，但对生存至关重要。在评估与污染相关的生态风险时，因此，考虑这些成本来评估压力源对种群的进化后果是相关的。然而,据我们所知,辐射环境中的进化对宿主防御的影响从未被研究过。使用实验进化方法，我们分析了暴露于0,1.4和50.0mGy的秀丽隐杆线虫种群20次转移(约20代)的适应度.h-1的137Csγ辐射。然后，来自转移17的种群被放置在相同的环境条件下，没有辐射(即，普通花园）大约10代，然后暴露于细菌寄生虫粘质沙雷氏菌，估计其存活率可以研究宿主防御。最后,我们研究了受辐照人群的适应性和宿主防御之间的进化权衡。
结果：我们发现与对照相比，两种辐照处理的适应度较低，但随着时间的推移，健身增加了50.0mGy。h-1，表明种群的局部适应。然后，对于以前在两种辐照处理下进化的普通花园种群，秀丽隐杆线虫对S.marcescens的存活率较低，表明在伽玛辐照环境中的演化对秀丽隐杆线虫的宿主防御有一定的代价。此外，我们显示了在多代实验结束时的标准化适应度与秀丽隐杆线虫在对照治疗中的存活率之间的权衡，但两种辐照处理的两种性状之间呈正相关。这些结果表明，在受辐照的人群中，那些对电离辐射最敏感的人也最容易感染病原体。另一方面,其他受辐照的人群似乎对两种应激因素都产生了交叉抗性。
结论：我们的研究表明，当出现新的压力源时，对环境压力源的适应可能与进化成本有关，甚至在第一个压力源结束后的几代人。在受辐照的人群中，我们观察到电离辐射抗性的演变，这似乎也提供了对抗病原体的优势。另一方面,一些受辐照的人群似乎积累了对应激源的敏感性。这项工作提供了一个新的论点，表明在生态毒理学和生态风险评估中考虑进化变化的重要性。
结果：我们发现与对照相比，两种辐照处理的适应度较低，但随着时间的推移，健身增加了50.0mGy。h-1，表明种群的局部适应。然后，对于以前在两种辐照处理下进化的普通花园种群，秀丽隐杆线虫对S.marcescens的存活率较低，表明在伽玛辐照环境中的演化对秀丽隐杆线虫的宿主防御有一定的代价。此外，我们显示了在多代实验结束时的标准化适应度与秀丽隐杆线虫在对照治疗中的存活率之间的权衡，但两种辐照处理的两种性状之间呈正相关。这些结果表明，在受辐照的人群中，那些对电离辐射最敏感的人也最容易感染病原体。另一方面,其他受辐照的人群似乎对两种应激因素都产生了交叉抗性。
结论：我们的研究表明，当出现新的压力源时，对环境压力源的适应可能与进化成本有关，甚至在第一个压力源结束后的几代人。在受辐照的人群中，我们观察到电离辐射抗性的演变，这似乎也提供了对抗病原体的优势。另一方面,一些受辐照的人群似乎积累了对应激源的敏感性。这项工作提供了一个新的论点，表明在生态毒理学和生态风险评估中考虑进化变化的重要性。
