Obligate brood parasitism, which refers to parasitic birds, fish, and insects that lay eggs in host nests, imposes strong selective pressure on hosts because the reproductive output of hosts is reduced considerably or eliminated completely while the foster parents provide extra-parental care to unrelated nestlings (Soler 2016). After parasites succeed in laying eggs, egg rejection by hosts plays an important role in avoiding parasitism by recognition and rejection of parasite eggs from host nests (Yang et al. 2014). Coevolution between brood parasites and hosts occurs in the great spotted cuckoo Clamator glandarius and the Eurasian magpie Pica pica is a classical parasite–host system. To counter cuckoo parasitism, Eurasian magpies were capable of attacking and expelling adult cuckoos from their nests, and recognizing and rejecting parasitic eggs by either visual or olfactory cues (Soler et al. 2014). However, these studies on Eurasian magpies all came from European populations, where parasitism is common in many populations. To understand coevolution between magpie hosts and cuckoo parasitism, it is necessary to investigate anti-parasitic defenses of magpies from other populations because behavior in 1 population may be totally different from that in other populations (Yang et al. 2015). Eurasian magpies have a wide distributional range across Europe and Asia, but great spotted cuckoos have a much narrower distribution of allopatry with the Asian population of magpies. It is necessary to study such Asian populations of magpies because anti-parasitism defenses would help us understand the coevolutionary interaction between magpies and cuckoos. For host populations that are allopatric with parasites and lack anti-parasite defenses, their absence of defenses can either be explained as (1) the loss of defenses after the release of parasitism pressure or (2) simply no evolution of defenses due to no contact with brood parasites. In contrast, some host populations that are allopatric with parasites or not exploited by parasites may retain their anti-parasitism defenses. Black-billed magpies Pica hudsonia and yellow-billed magpies P. nutalli are closely related to Eurasian magpies, but only distributed in America. Both are allopatric with great spotted cuckoos and not used by any cuckoo species. Still, they possess 100% egg recognition capacity, which is higher than that of Eurasian magpies (Soler 2016).

中文翻译：

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亚洲喜鹊种群缺乏抗寄生虫防御，喜鹊是欧洲大斑杜鹃的常规宿主

专性巢寄生是指寄生在寄主巢穴中产卵的鸟类、鱼类和昆虫，由于寄主的生殖量大大减少或完全消除，而寄养父母对无关的亲代提供额外的照顾，对寄主施加强烈的选择压力。雏鸟（Soler 2016）。寄生虫成功产卵后，宿主的卵排斥通过识别和排斥来自宿主巢穴的寄生虫卵在避免寄生方面发挥重要作用（Yang et al. 2014）。寄生蜂和寄主之间的共同进化发生在大斑杜鹃Clamator geararius和欧亚喜鹊Pica pica 中是一个经典的寄生虫-宿主系统。为了对抗杜鹃寄生，欧亚喜鹊能够攻击并从巢穴中驱逐成年杜鹃，并通过视觉或嗅觉线索识别和拒绝寄生卵（Soler et al. 2014）。然而，这些对欧亚喜鹊的研究都来自欧洲种群，在那里寄生在许多种群中很常见。要了解喜鹊宿主和杜鹃寄生之间的协同进化，有必要研究其他种群喜鹊的抗寄生虫防御能力，因为 1 个种群的行为可能与其他种群的行为完全不同（Yang 等人，2015 年）。欧亚喜鹊在欧洲和亚洲的分布范围很广，但大斑杜鹃与亚洲喜鹊种群的异域分布要窄得多。有必要研究这些亚洲喜鹊种群，因为抗寄生虫防御将帮助我们了解喜鹊和杜鹃之间的共同进化相互作用。对于异源性寄生虫且缺乏抗寄生虫防御能力的宿主种群，他们缺乏防御能力可以解释为（1）释放寄生压力后防御能力的丧失，或（2）由于没有接触而没有防御能力的进化带有寄生虫。相比之下，一些异域寄生虫或未被寄生虫利用的宿主种群可能会保留其抗寄生虫防御能力。黑嘴喜鹊 对于异源性寄生虫且缺乏抗寄生虫防御的宿主种群，其缺乏防御可以解释为（1）释放寄生压力后防御丧失或（2）由于没有接触而没有防御进化带有寄生虫。相比之下，一些异域寄生虫或未被寄生虫利用的宿主种群可能会保留其抗寄生虫防御能力。黑嘴喜鹊 对于异源性寄生虫且缺乏抗寄生虫防御的宿主种群，其缺乏防御可以解释为（1）释放寄生压力后防御丧失或（2）由于没有接触而没有防御进化带有寄生虫。相比之下，一些异域寄生虫或未被寄生虫利用的宿主种群可能会保留其抗寄生虫防御能力。黑嘴喜鹊Pica hudsonia和黄嘴喜鹊P. nutalli与欧亚喜鹊关系密切，但仅分布于美洲。两者都是异域的，有大斑杜鹃，任何杜鹃物种都不使用。尽管如此，它们仍具有 100% 的鸡蛋识别能力，高于欧亚喜鹊（Soler 2016）。