The evolution of virulence when parasites cause host castration and gigantism
The evolution of virulence when parasites cause host castration and gigantism
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DOI：
10.1086/424606
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发表时间：
2004-11-01
影响因子：
2.9
通讯作者：
Decaestecker, E
中科院分区：
文献类型：
--
作者：
Ebert, D;Carius, HJ;Decaestecker, E
有人认为，寄生虫对宿主的危害是寄生虫繁殖的不可避免的后果，不仅对宿主，而且对寄生虫也有代价。阉割寄生虫被认为是通过降低宿主繁殖力来最大限度地减少其成本，这可能会最大限度地减少过早杀死宿主和寄生虫的机会。我们进行了一系列的实验，以了解阉割细菌的毒性在浮游甲壳动物大型蚤的进化。通过在感染D.结果表明，两种拮抗菌都是资源有限的，宿主和寄生虫的繁殖之间存在负相关，表明拮抗菌之间存在资源竞争。多枝巴氏杆菌还诱导其宿主的生长增强（寄生性），我们发现这与宿主繁殖力呈负相关，但与寄生虫繁殖呈正相关。由于受感染的宿主从未从感染中恢复过来，我们得出结论，寄生虫只对寄生虫有益。然而，进化出了反适应。我们发现，受感染的主机已增强生殖阉割前。这种向早期繁殖的转变增加了宿主的繁殖力，并损害了寄生虫的繁殖。最后，我们发现，这种资源冲突是受宿主和寄生虫基因型之间的遗传变异的人口，因此可能是一个重要的力量，在这个系统中的毒力的共同进化。提出了一个言语模型，并表明巨人症的适应价值是储存宿主资源，这些资源在寄生虫阉割后被释放出来，供生长的寄生虫使用。这一假设假定感染是持久的，也就是说，它们具有很高的预期寿命。
It has been suggested that the harm parasites cause to their hosts is an unavoidable consequence of parasite reproduction with costs not only for the host but also for the parasite. Castrating parasites are thought to minimize their costs by reducing host fecundity, which may minimize the chances of killing both host and parasite prematurely. We conducted a series of experiments to understand the evolution of virulence of a castrating bacterium in the planktonic crustacean Daphnia magna. By manipulating food levels during the infection of D. magna with the bacterium Pasteuria ramosa, we showed that both antagonists are resource-limited and that a negative correlation between host and parasite reproduction exists, indicating resource competition among the antagonists. Pasteuria ramosa also induces enhanced growth of its hosts (gigantism), which we found to be negatively correlated with host fecundity but positively correlated with parasite reproduction. Because infected hosts never recovered from infections, we concluded that gigantism is beneficial only for the parasite. Hosts, however, have evolved counter-adaptations. We showed that infected hosts have enhanced reproduction before castration. This shift to earlier reproduction increases overall host fecundity and compromises parasite reproduction. Finally, we showed that this resource conflict is subject to genetic variation among host and parasite genotypes within a population and is therefore likely to be an important force in the coevolution of virulence in this system. A verbal model is presented and suggests that the adaptive value of gigantism is to store host resources, which are liberated after parasitic castration for later use by the growing parasite. This hypothesis assumes that infections are long lasting, that is, that they have a high life expectancy.