Data from: Decomposing parasite fitness reveals the basis of specialization in a two‐host, two‐parasite system

The ecological specialization of parasites - whether they can obtain high fitness on very few or very many different host species - is a determining feature of their ecology. In order to properly assess specialization, it is imperative to measure parasite fitness across host species; to understand its origins, fitness must be decomposed into the underlying traits. Despite the omnipresence of parasites with multiple hosts, very few studies assess and decompose their specialization in this way. To bridge this gap, we quantified the infectivity, virulence, and transmission rate of two parasites, the horizontally transmitted microsporidians Anostracospora rigaudi and Enterocytospora artemiae, in their natural hosts, the brine shrimp Artemia parthenogenetica and Artemia franciscana. Our results demonstrate that each parasite performs well on one of the two host species (A. rigaudi on A. parthenogenetica, and E. artemiae on A. franciscana), and poorly on the other. This partial specialization is driven by high infectivity and transmission rates in the preferred host, and is associated with maladaptive virulence and large costs of resistance in the other. Our study represents a rare empirical contribution to the study of parasite evolution in multi-host systems, highlighting the negative effects of under- and over-exploitation when adapting to multiple hosts.

寄生虫的生态特化——即它们仅能在极少数宿主物种中获得高适合度，抑或可在众多不同宿主中达成高适合度——是其生态学的决定性特征。若要准确评估特化程度，必须测定寄生虫在各类宿主物种中的适合度；若要阐明其演化起源，则需将适合度拆解为其背后的核心性状。尽管多宿主寄生虫极为普遍，但极少有研究以此方式评估并拆解其特化程度。为填补这一研究空白，我们针对两种水平传播的微孢子虫（microsporidians）：*Anostracospora rigaudi*与*Enterocytospora artemiae*，在其自然宿主孤雌生殖卤虫（Artemia parthenogenetica）和弗兰西斯卡卤虫（Artemia franciscana）体内的感染性、毒力及传播速率开展了量化测定。研究结果表明，每种寄生虫仅在其中一种宿主中表现优异：*Anostracospora rigaudi*在孤雌生殖卤虫中适配性极佳，而*Enterocytospora artemiae*则在弗兰西斯卡卤虫中表现出色，反之在另一种宿主中性能低下。这种部分特化现象，源于寄生虫在偏好宿主中具备较高的感染性与传播速率，而在非偏好宿主中则伴随适应不良的毒力以及高昂的抗性代价。本研究为多宿主系统中的寄生虫演化研究提供了罕见的实证支撑，同时揭示了宿主适配过程中利用不足与过度利用所带来的负面影响。