Parasite-mediated selection may initiate or enhance differentiation between host populations that are exposed to different parasite infections. Variation in infection among populations may result from differences in host ecology (thereby exposure to certain parasites) and/or intrinsic immunological traits. Species of cichlid fish, even when recently diverged, often differ in parasite infection, but the contributions of intrinsic and extrinsic causes are unknown. Here, we compare infection patterns between two closely related host species from Lake Victoria (genus Pundamilia), using wild-caught and first-generation laboratory-reared fish, as well as laboratory-reared hybrids. Three of the commonest ectoparasite species observed in the wild were also present in the laboratory populations. However, the infection differences between the host species as observed in the wild were not maintained in laboratory conditions. In addition, hybrids did not differ in infection from either parental species. These findings suggest that the observed species differences in infection in the wild might be mainly driven by ecology-related effects (i.e. differential exposure), rather than by intrinsic species differences in immunological traits. Thus, while there is scope for parasite-mediated selection in Pundamilia in the wild, it has apparently not yet generated divergent evolutionary responses and may not enhance assortative mating among closely related species.

中文翻译：

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野生捕获和实验室饲养的丽鱼及其杂交种的体外寄生虫感染模式表明，感染的物种差异是外在原因，而不是内在原因


寄生虫介导的选择可以启动或增强暴露于不同寄生虫感染的宿主群体之间的分化。人群之间感染的差异可能是由于宿主生态学（从而暴露于某些寄生虫）和/或内在免疫学特征的差异造成的。丽鱼科鱼的物种，即使最近出现分歧，在寄生虫感染方面也常常有所不同，但内在和外在原因的贡献尚不清楚。在这里，我们使用野生捕获的鱼和第一代实验室饲养的鱼以及实验室饲养的杂交鱼，比较了维多利亚湖中两种密切相关的宿主物种（Pundamilia）之间的感染模式。在野外观察到的三种最常见的体外寄生虫物种也存在于实验室种群中。然而，在野外观察到的宿主物种之间的感染差异在实验室条件下并不能维持。此外，杂交种在感染方面与亲本物种没有差异。这些发现表明，观察到的野生感染物种差异可能主要是由生态相关效应（即差异暴露）驱动的，而不是由免疫特征的固有物种差异驱动的。因此，虽然在野生的 Pundamilia 中存在寄生虫介导的选择范围，但它显然尚未产生不同的进化反应，并且可能不会增强密切相关的物种之间的选型交配。