Testing Local Adaptation in a Natural Great Tit-Malaria System: An Experimental Approach

Finding out whether Plasmodium spp. are coevolving with their vertebrate hosts is of both theoretical and applied interest and can influence our understanding of the effects and dynamics of malaria infection. In this study, we tested for local adaptation as a signature of coevolution between malaria blood parasites, Plasmodium spp. and its host, the great tit, Parus major. We conducted a reciprocal transplant experiment of birds in the field, where we exposed birds from two populations to Plasmodium parasites. This experimental set-up also provided a unique opportunity to study the natural history of malaria infection in the wild and to assess the effects of primary malaria infection on juvenile birds. We present three main findings: i) there was no support for local adaptation; ii) there was a male-biased infection rate; iii) infection occurred towards the end of the summer and differed between sites. There were also site-specific effects of malaria infection on the hosts. Taken together, we present one of the few experimental studies of parasite-host local adaptation in a natural malaria system, and our results shed light on the effects of avian malaria infection in the wild.探究疟原虫属（Plasmodium spp.）是否与其脊椎动物宿主协同进化，兼具理论与应用价值，且可深化我们对疟疾感染效应与动态的认知。本研究以血液寄生疟原虫——疟原虫属（Plasmodium spp.）及其宿主大山雀（Parus major）为研究对象，以本地适应（local adaptation）作为二者协同进化的标志性特征，检验其是否存在本地适应现象。我们开展了野外鸟类互易移植实验，将两个种群的鸟类暴露于疟原虫感染环境中。该实验设计同时为我们提供了独特契机，可用于研究野外疟疾感染的自然史，并评估初次疟疾感染对幼鸟的影响。本研究得到三项核心结论：其一，未发现支持本地适应的证据；其二，感染率呈雄性偏向性；其三，感染多发生于夏末，且不同样地间存在差异。疟疾感染对宿主的影响亦存在样地特异性。综上，本研究是自然疟疾系统中开展寄生虫-宿主本地适应实验研究的为数不多的案例之一，研究结果阐明了野外环境中禽疟疾感染的效应。