Data from: On the equivalence of host local adaptation and parasite maladaptation: an experimental test

In spatio-temporally varying environments, host-parasite coevolution may lead to either host or parasite local adaptation. Using reciprocal infestations over 11 pairs of plots, we tested local adaptation in the hen flea and its main host, the great tit. Flea reproductive success (number of adult at host fledging) was lower on host individuals from the same plot compared to foreign hosts (from another plot), revealing flea local maladaptation. Host reproductive success (number of fledged young) was lower for nests infested by foreign fleas compared to controls, with an intermediate success for nests infested by local fleas. This suggests host local adaptation although the absence of local adaptation could not be excluded. However, fledglings were heavier and larger when reared with foreign compared to local fleas, which could also indicate host local maladaptation if the fitness gain in offspring size offsets the potential cost in offspring number. Our results therefore challenge the traditional view that parasite local maladaptation is equivalent to host local adaptation. The differences in fledgling morphology between nests infested with local and foreign fleas suggest that flea origin affects host resource allocation strategy between nestling growth and defense against parasites. Therefore determining the mechanisms that underlie these local adaptation patterns requires the identification of the relevant fitness measures and life-history trade-offs in both species.

在时空动态变化的环境中，宿主与寄生虫的协同进化可能会导致宿主或寄生虫产生局部适应性（local adaptation）。本研究通过对11组样地开展互惠侵染实验（reciprocal infestations），检测了禽蚤（hen flea）及其主要宿主大山雀（great tit）的局部适应性。禽蚤的繁殖成功率以宿主雏鸟出飞时的成虫数量计：相较于来自其他样地的异源宿主，同一样地宿主上的禽蚤繁殖成功率更低，这表明禽蚤出现了局部适应不良（local maladaptation）。宿主的繁殖成功率以出飞幼鸟数量计：相较于对照组，被异源蚤侵染的鸟巢对应的宿主繁殖成功率更低，而被本地蚤侵染的鸟巢对应的宿主繁殖成功率处于中间水平。这提示宿主存在局部适应性，但仍无法完全排除宿主未产生局部适应性的可能性。不过，与本地蚤侵染组相比，异源蚤侵染组抚育的幼鸟体重更大、体型更健壮；若幼鸟体型带来的适合度收益能够抵消幼鸟数量减少的潜在成本，则该结果同样可提示宿主局部适应不良。因此，本研究结果对"寄生虫局部适应不良等同于宿主局部适应性"这一传统观点提出了挑战。本地蚤与异源蚤侵染的鸟巢间，幼鸟形态存在显著差异，这表明蚤的来源会影响宿主在雏鸟生长与抗寄生虫防御之间的资源分配策略。因此，要阐明这些局部适应性模式背后的机制，需明确两个物种的关键适合度指标以及生活史权衡关系。