Wegner K Mathias, Berenos Camillo, Schmid-Hempel Paul
Experimental Ecology, Institute of Integrative Biology, ETH Zürich, Switzerland.
Evolution. 2008 Sep;62(9):2381-92. doi: 10.1111/j.1558-5646.2008.00444.x. Epub 2008 Jun 28.
Genetically coupled antagonistic coevolution between host and parasites can select for the maintenance of recombination in the host. Mechanistically, maintenance of recombination relies on epistatic interactions between resistance genes creating linkage disequilibria (LD). The role of epistasis in host resistance traits is however only partly understood. Therefore, we applied the joint scaling principle to assess epistasis and other nonadditive genetic components of two resistance traits, survival, and parasite spore load, in population crosses of the red flour beetle Tribolium castanaeum under infections with the microsporidian Nosema whitei. We found nonadditive components only in infected populations but not in control populations. The genetic architecture underlying survival under parasite infection was more complex than that of spore load. Accordingly, the observed negative correlation between survival and spore load was mainly based on a correlation between shared additive components. Breakdown of resistance was especially strong in F2 crosses between resistant lines indicating that multiple epistatic routes can lead to the same adaptation. In general, the wide range of nonoverlapping genetic components between crosses indicated that parasite resistance in T. castanaeum can be understood as a multi peaked fitness landscape with epistasis contributing substantially to phenotypic differentiation in resistance.
宿主与寄生虫之间的基因耦合拮抗协同进化可以选择维持宿主中的重组。从机制上讲，重组的维持依赖于抗性基因之间的上位性相互作用，从而产生连锁不平衡（LD）。然而，上位性在宿主抗性性状中的作用仅得到部分理解。因此，我们应用联合尺度原理来评估在受到微孢子虫白氏 Nosema 感染的赤拟谷盗 Tribolium castanaeum 种群杂交中，两个抗性性状（存活率和寄生虫孢子负荷）的上位性及其他非加性遗传成分。我们发现仅在受感染种群中存在非加性成分，而在对照种群中则没有。寄生虫感染下存活的遗传结构比孢子负荷的遗传结构更复杂。因此，观察到的存活率与孢子负荷之间的负相关主要基于共享加性成分之间的相关性。抗性品系之间的 F2 杂交中抗性的崩溃尤为强烈，这表明多种上位性途径可导致相同的适应性。总体而言，杂交之间广泛的非重叠遗传成分表明，赤拟谷盗中的寄生虫抗性可被理解为一个多峰适应度景观，上位性对抗性的表型分化有很大贡献。
