Kraaijeveld A R, Godfray H C
NERC Centre for Population Biology, Imperial College at Silwood Park, Berkshire, UK.
Nature. 1997 Sep 18;389(6648):278-80. doi: 10.1038/38483.
The extent to which an organism is selected to invest in defences against pathogens and parasites depends on the advantages that ensue should infection occur, but also on the costs of maintaining defences in the absence of infection. The presence of heritable variation in resistance suggests that costs exist, but we know very little about the nature or magnitude of these costs in natural populations of animals. A powerful technique for identifying trade-offs between fitness components is the study of correlated responses to artificial selection. We have selected Drosophila melanogaster for improved resistance against an endoparasitoid, Asobara tabida. Endoparasitoids are insects whose larvae develop internally within the body of other insects, eventually killing them, although their hosts can sometimes survive attack by mounting a cellular immune response. We found that reduced larval competitive ability in unparasitized D. melanogaster is a correlated response to artificial selection for improved resistance against A. tabida. The strength of selection for competitive ability and parasitoid resistance is likely to vary temporally and spatially, which may explain the observed heritable variation in resistance.
生物体被选择投入资源用于抵御病原体和寄生虫的程度，不仅取决于感染发生时随之而来的益处，还取决于在未感染时维持防御的成本。抗性中可遗传变异的存在表明成本是存在的，但我们对动物自然种群中这些成本的性质或大小知之甚少。一种用于识别适合度成分之间权衡取舍的强大技术是对人工选择的相关反应进行研究。我们对黑腹果蝇进行了选择，以提高其对一种内寄生蜂——塔氏阿索斯茧蜂的抗性。内寄生蜂是一类昆虫，其幼虫在其他昆虫体内发育，最终导致宿主死亡，不过宿主有时可以通过产生细胞免疫反应在攻击中存活下来。我们发现，在未被寄生的黑腹果蝇中，幼虫竞争能力的降低是对提高对塔氏阿索斯茧蜂抗性的人工选择的一种相关反应。对竞争能力和对寄生蜂抗性的选择强度可能会随时间和空间而变化，这或许可以解释所观察到的抗性中的可遗传变异。
