Within animal hybrid zones, parasites may determine competitive outcomes between host species and thus affect hybridization dynamics. We addressed this hypothesis by evaluating haemosporidian prevalence and community composition in a rapidly moving hybrid zone between Black-capped Chickadees (Poecile atricapillus) and Carolina Chickadees (P. carolinensis). Using molecular methods, we screened for haemosporidians in multiple chickadee populations across the hybrid zone and investigated whether parasite prevalence varied as a function of admixture among these birds. We identified 36 parasite lineages from 3 haemosporidian genera (Plasmodium, Haemoproteus, and Leucocytozoon) but found no genera or lineages more likely to infect any particular chickadee taxon. Instead, haemosporidian prevalence varied across sites and seasons: Leucocytozoon was more prevalent during chickadees’ breeding season, whereas Haemoproteus prevalence peaked during nonbreeding periods. Leucocytozoon infected proportionally fewer birds at the leading edge of the hybrid zone than near its center. However, haemosporidian communities were similar among chickadee populations, and evidence for parasite exchanges between chickadee taxa was lacking. These results underscore the complexity of bird–parasite relationships and suggest that haemosporidians are unlikely to play a major role in the ongoing movement of this hybrid zone.

中文翻译：

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山雀杂交区的血孢子虫流行率和群落组成变化不大

在动物杂交区内，寄生虫可能决定宿主物种之间的竞争结果，从而影响杂交动态。我们通过评估黑冠山雀 (Poecile atricapillus) 和卡罗莱纳山雀 (P. carolinensis) 之间快速移动的混合区中的血孢子虫流行率和群落组成来解决这一假设。使用分子方法，我们在杂交区的多个山雀种群中筛选了血孢子虫，并研究了寄生虫流行率是否随这些鸟类的混合而变化。我们从 3 个血孢子虫属（疟原虫属、血孢子虫属和白细胞虫属）中鉴定了 36 个寄生虫谱系，但没有发现更可能感染任何特定山雀分类群的属或谱系。相反，血孢子虫患病率因地点和季节而异：白细胞虫在山雀的繁殖季节更为普遍，而血变形虫的流行在非繁殖期达到顶峰。白细胞虫感染混合区前缘的鸟类比其中心附近的鸟类少。然而，山雀种群之间的血孢子虫群落相似，并且缺乏山雀类群之间寄生虫交换的证据。这些结果强调了鸟类-寄生虫关系的复杂性，并表明血孢子虫不太可能在这个混合区的持续运动中发挥主要作用。山雀种群中的血孢子虫群落相似，并且缺乏山雀类群之间寄生虫交换的证据。这些结果强调了鸟类-寄生虫关系的复杂性，并表明血孢子虫不太可能在这个混合区的持续运动中发挥主要作用。山雀种群中的血孢子虫群落相似，并且缺乏山雀类群之间寄生虫交换的证据。这些结果强调了鸟类-寄生虫关系的复杂性，并表明血孢子虫不太可能在这个混合区的持续运动中发挥主要作用。