Despite the significant effect of host-parasite interactions on both ecological systems and organism health, there is still limited understanding of the mechanisms driving evolution of host resistance to parasites. One model of rapid evolution, the Baldwin Effect, describes the role of plasticity in adaptation to novel conditions, and subsequent canalization of associated traits. While mostly applied in the context of environmental conditions, this theory may be relevant to the evolution of host resistance to novel parasites. Here we test the applicability of the Baldwin Effect to the evolution of resistance in a natural system using threespine stickleback fish (Gasterosteus aculeatus) and their cestode parasite Schistochephalus solidus. We leverage a large transcriptomic data set to describe the response to S. solidus infection by three different genetic crosses of stickleback, from a resistant and a tolerant population. Hosts mount a multi-genic response to the parasite that is similar among host genotypes. In addition, we document extensive constitutive variation in gene expression among host genotypes. However, although many genes are both infection-induced and differentially expressed between genotypes, this overlap is not more extensive than expected by chance. We also see little evidence of canalization of infection-induced gene expression in the derived resistant population. These patterns do not support the Baldwin Effect, though they illustrate the importance of variation in both constitutive expression and induced responses to parasites. Finally, our results improve understanding of the cellular mechanisms underlying a putative resistance phenotype (fibrosis). Combined, our results highlight the importance of both constitutive and inducible variation in the evolution of resistance to parasites, and identify new target genes contributing to fibrosis. These findings advance understanding of host-parasite interactions and co-evolutionary relationships in natural systems.

中文翻译：

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鲍德温效应的检验：组成型表达和对寄生虫的诱导反应的差异是宿主对寄生虫反应的差异的基础

尽管寄主-寄生虫相互作用对生态系统和生物健康均具有重大影响，但对驱动寄主对寄生虫的抗性进化的机制的了解仍然有限。快速发展的模型之一鲍德温效应（Baldwin Effect）描述了可塑性在适应新条件以及随后的相关性状渠化方面的作用。尽管该理论主要应用于环境条件，但可能与宿主对新型寄生虫的抗性进化有关。在这里，我们测试鲍德温效应对使用三脊刺背鳍鱼（Gasterosteus aculeatus）及其尾est寄生虫Schistochephalus solidus的抵抗力进化的适用性。我们利用大量的转录组数据集来描述对固相线虫的反应来自三个耐药性和耐受性人群的棘背genetic不同遗传交叉感染。宿主对寄生虫的多基因反应与宿主基因型相似。此外，我们记录了宿主基因型之间基因表达的广泛组成型变异。然而，尽管许多基因都是感染诱导的，并且在基因型之间差异表达，但是这种重叠并不比偶然的预期更广泛。我们还没有看到在衍生的耐药人群中感染诱导的基因表达的渠道化的证据。这些模式不支持鲍德温效应，尽管它们说明了组成型表达和对寄生虫的诱导反应中变异的重要性。最后，我们的结果提高了对潜在的耐药表型（纤维化）的细胞机制的了解。结合起来，我们的结果突出了在对寄生虫的抗性进化中本构和可诱导变异的重要性，并确定了导致纤维化的新靶基因。这些发现促进了对自然系统中宿主-寄生虫相互作用和共同进化关系的理解。