Vijendravarma Roshan K, Kraaijeveld Alex R, Godfray H C J
NERC Centre for Population Biology, Imperial College London, Silwood Park Campus, Berks, United Kingdom.
Evolution. 2009 Jan;63(1):104-14. doi: 10.1111/j.1558-5646.2008.00516.x. Epub 2008 Sep 11.
Most organisms experience strong selection to develop mechanisms to resist or tolerate their pathogens or parasites. Limits to adaptation are set by correlated responses to selection, for example reduced abilities to detect other parasites or trade-offs with other fitness components. For a few model systems it is now becoming possible to compare the evolutionary response to a broad range of natural enemies. In Drosophila, the evolutionary responses to ectoparasitic mites, parasitoids, and fungal and bacterial pathogens have previously been studied. Here replicate lines of D. melanogaster were exposed to the microsporidian parasite Tubulinosema kingi over a period of 61 weeks, with overlapping generations. Compared to controls, exposed lines had higher early-life fecundity and increased longevity when infected suggesting successful selection for resistance or tolerance. In the absence of the pathogen, exposed lines had lower fecundity when reared under harsh environmental conditions, and were poorer larval competitors than controls. They also had relatively higher densities of haemocytes, a component of the cellular immune system. Defense against this pathogen resembles more that against macroparasites than microsparasites, and this is interpreted in the light of what is known about the mechanisms of resistance to microsporidians.
大多数生物体都会经历强烈的选择，以发展出抵抗或耐受其病原体或寄生虫的机制。适应的局限性由对选择的相关反应设定，例如检测其他寄生虫的能力降低或与其他适合度成分的权衡。对于一些模型系统来说，现在有可能比较对广泛的天敌的进化反应。在果蝇中，此前已经研究了对外寄生螨、寄生蜂以及真菌和细菌病原体的进化反应。在这里，黑腹果蝇的重复品系在61周的时间里，历经重叠世代，暴露于微孢子虫寄生虫金氏管微孢子虫之下。与对照组相比，暴露组在感染时具有更高的早期繁殖力和更长的寿命，这表明成功选择了抗性或耐受性。在没有病原体的情况下，暴露组在恶劣环境条件下饲养时繁殖力较低，并且作为幼虫时的竞争力比对照组差。它们还具有相对较高密度的血细胞，这是细胞免疫系统的一个组成部分。针对这种病原体的防御更类似于针对大型寄生虫而非微寄生虫的防御，这是根据已知的对微孢子虫的抗性机制来解释的。
