Data from: Song sparrows Melospiza melodia have a home-field advantage in defending against sympatric malarial parasites

Hosts and parasites interact on both evolutionary and ecological timescales. The outcome of these interactions, specifically whether hosts are more resistant to their local parasites (sympatric) than to parasites from another location (allopatric), is likely to affect the spread of infectious disease and the fitness consequences of host dispersal. We conducted a cross-infection experiment to determine whether song sparrows (Melospiza melodia) have an advantage in dealing with sympatric parasites. We captured birds from two breeding sites 437 km apart, and inoculated them with avian malaria (Plasmodium spp.) cultured either from their capture site or from the other site. Infection risk was lower for birds exposed to sympatric than to allopatric Plasmodium lineages, suggesting that song sparrows may have a home-field advantage in defending against local parasite strains. This pattern was more pronounced at one capture site than at the other, consistent with mosaic models of host–parasite interactions. Home-field advantage may arise from evolutionary processes, whereby host populations become adapted to their local parasites, and/or from ecological interactions, whereby host individuals develop resistance to the local parasites through previous immune exposure. Our findings suggest that greater susceptibility to novel parasites may represent a fitness consequence of natal dispersal.宿主与寄生虫在进化与生态两个时间尺度上均存在相互作用。这类相互作用的结局，即宿主对本地寄生虫（同域，sympatric）的抗性是否强于异地寄生虫（异域，allopatric），大概率会影响传染病的传播与宿主扩散的适合度后果。我们开展了一项交叉感染实验，旨在探究歌带鹀（Melospiza melodia）在应对同域寄生虫时是否存在优势。我们从相距437公里的两个繁殖栖息地捕捉个体，分别使用源自其捕获位点或另一捕获位点的禽疟原虫（Plasmodium spp.）培养物进行接种。相较于暴露于异域疟原虫谱系的个体，接触同域疟原虫谱系的歌带鹀感染风险更低，这表明歌带鹀在抵御本地寄生虫株系时或存在主场优势。该效应在其中一个捕获位点表现得更为显著，这与宿主-寄生虫相互作用的镶嵌模型（mosaic models of host–parasite interactions）相符。主场优势的产生可归因于两类过程：一是宿主种群对本地寄生虫产生适应性的进化过程，二是宿主个体通过既往免疫暴露获得对本地寄生虫抗性的生态相互作用过程。本研究结果表明，对新型寄生虫的更高易感性，可能是出生扩散（natal dispersal）所带来的适合度后果。