Data from: Genetic architecture of resistance in Daphnia hosts against two species of host-specific parasites

Understanding the genetic architecture of host resistance is key for understanding the evolution of host–parasite interactions. Evolutionary models often assume simple genetics based on few loci and strong epistasis. It is unknown, however, whether these assumptions apply to natural populations. Using a quantitative trait loci (QTL) approach, we explore the genetic architecture of resistance in the crustacean Daphnia magna to two of its natural parasites: the horizontally transmitted bacterium Pasteuria ramosa and the horizontally and vertically transmitted microsporidium Hamiltosporidium tvaerminnensis. These two systems have become models for studies on the evolution of host–parasite interactions. In the QTL panel used here, Daphnia’s resistance to P. ramosa is controlled by a single major QTL (which explains 50% of the observed variation). Resistance to H. tvaerminnensis horizontal infections shows a signature of a quantitative trait based in multiple loci with weak epistatic interactions (together explaining 38% variation). Resistance to H. tvaerminnensis vertical infections, however, shows only one QTL (explaining 13.5% variance) that colocalizes with one of the QTLs for horizontal infections. QTLs for resistance to Pasteuria and Hamiltosporidium do not colocalize. We conclude that the genetics of resistance in D. magna are drastically different for these two parasites. Furthermore, we infer that based on these and earlier results, the mechanisms of coevolution differ strongly for the two host–parasite systems. Only the Pasteuria–Daphnia system is expected to follow the negative frequency-dependent selection (Red Queen) model. How coevolution works in the Hamiltosporidium–Daphnia system remains unclear.解析宿主抗性的遗传结构，是理解宿主-寄生虫互作演化的关键所在。进化模型往往基于少数基因座与强上位性的简单遗传假设构建，但此类假设是否适用于自然种群仍未明确。本研究采用数量性状基因座 (quantitative trait loci, QTL) 分析方法，以甲壳动物大型溞 (Daphnia magna) 为研究对象，探究其对两种天然寄生虫的抗性遗传结构：一种为水平传播的细菌拉氏巴斯德菌 (Pasteuria ramosa)，另一种为兼具水平与垂直传播能力的微孢子虫特韦尔明内汉密尔顿微孢子虫 (Hamiltosporidium tvaerminnensis)。上述两种宿主-寄生虫互作体系已成为演化生物学研究的经典模型。在本研究使用的QTL定位群体中，大型溞对拉氏巴斯德菌的抗性由单个主效QTL控制，该基因座可解释观测到的50%表型变异。大型溞对特韦尔明内汉密尔顿微孢子虫水平感染的抗性表现为多基因座控制的数量性状特征，且上位性交互作用较弱，所有相关QTL累计可解释38%的表型变异。而针对该微孢子虫垂直感染的抗性，仅检测到单个QTL，其定位区间与该微孢子虫水平感染抗性相关的其中一个QTL重合。此外，抗拉氏巴斯德菌与抗特韦尔明内汉密尔顿微孢子虫的QTL并无共定位现象。综上，大型溞对这两种寄生虫的抗性遗传机制存在显著差异。结合本研究与既往研究结果，我们进一步推断，这两种宿主-寄生虫互作体系的协同演化机制亦存在显著分歧。仅拉氏巴斯德菌-大型溞体系符合负频率依赖选择 (negative frequency-dependent selection, Red Queen) 模型的理论预期。而特韦尔明内汉密尔顿微孢子虫-大型溞体系的协同演化模式仍有待阐明。