Gut microbiota are essential for host health and survival, but we are still far from understanding the processes involved in shaping their composition and evolution. Controlled experimental work under lab conditions as well as human studies pointed at environmental factors (i.e., diet) as the main determinant of the microbiota with little evidence of genetic effects, while comparative interspecific studies detected significant phylogenetic effects. Different species, however, also differ in diet, feeding behavior, and environmental characteristics of habitats, all of which also vary interspecifically, and, therefore, can potentially explain most of the detected phylogenetic patterns. Here, we take advantage of the reproductive strategy of avian brood parasites and investigate gut microbiotas (esophageal (food and saliva) and intestinal) of great spotted cuckoo (Clamator glandarius) and magpie (Pica pica) nestlings that grow in the same nests. We also estimated diet received by each nestling and explored its association with gut microbiota characteristics. Although esophageal microbiota of magpies and great spotted cuckoos raised within the same environment (nest) did not vary, the microbiota of cloacal samples showed clear interspecific differences. Moreover, diet of great spotted cuckoo and magpie nestlings explained the microbiota composition of esophageal samples, but not of cloaca samples. These results strongly suggest a genetic component determining the intestinal microbiota of host and parasitic bird species, indicating that interspecific differences in gut morphology and physiology are responsible for such interspecific differences.

肠道微生物群对于宿主的健康和生存至关重要，但我们距离了解其组成和进化的过程还很遥远。实验室条件下的对照实验工作以及人类研究都指出环境因素（即饮食）是微生物群的主要决定因素，几乎没有遗传影响的证据，而比较种间研究则发现了显着的系统发育影响。然而，不同的物种在饮食、摄食行为和栖息地的环境特征方面也有所不同，所有这些在种间也有所不同，因此可以潜在地解释大多数检测到的系统发育模式。在这里，我们利用禽类寄生虫的繁殖策略，研究了生长在同一巢中的大斑杜鹃 ( Clamator mudarius ) 和喜鹊 ( Pica pica ) 雏鸟的肠道微生物群（食道（食物和唾液）和肠道）。我们还估计了每只雏鸟的饮食，并探讨了其与肠道微生物群特征的关系。尽管在同一环境（巢）中饲养的喜鹊和大斑杜鹃的食道微生物群没有变化，但泄殖腔样本的微生物群显示出明显的种间差异。此外，大斑杜鹃和喜鹊雏鸟的饮食可以解释食道样本的微生物群组成，但不能解释泄殖腔样本的微生物群组成。这些结果强烈表明，遗传成分决定了宿主和寄生鸟类的肠道微生物群，表明肠道形态和生理学的种间差异是造成这种种间差异的原因。