Department of Ecology, Tibetan Centre for Ecology and Conservation at WHU-TU, Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Wuhan University, Wuhan, China.
Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, China.
Mol Biol Evol. 2021 Aug 23;38(9):3649-3663. doi: 10.1093/molbev/msab130.
Obligate scavenging on the dead and decaying animal matter is a rare dietary specialization that in extant vertebrates is restricted to vultures. These birds perform essential ecological services, yet many vulture species have undergone recent steep population declines and are now endangered. To test for molecular adaptations underlying obligate scavenging in vultures, and to assess whether genomic features might have contributed to their population declines, we generated high-quality genomes of the Himalayan and bearded vultures, representing both independent origins of scavenging within the Accipitridae, alongside a sister taxon, the upland buzzard. By comparing our data to published sequences from other birds, we show that the evolution of obligate scavenging in vultures has been accompanied by widespread positive selection acting on genes underlying gastric acid production, and immunity. Moreover, we find evidence of parallel molecular evolution, with amino acid replacements shared among divergent lineages of these scavengers. Our genome-wide screens also reveal that both the Himalayan and bearded vultures exhibit low levels of genetic diversity, equating to around a half of the mean genetic diversity of other bird genomes examined. However, demographic reconstructions indicate that population declines began at around the Last Glacial Maximum, predating the well-documented dramatic declines of the past three decades. Taken together, our genomic analyses imply that vultures harbor unique adaptations for processing carrion, but that modern populations are genetically depauperate and thus especially vulnerable to further genetic erosion through anthropogenic activities.
以死亡和腐烂的动物尸体为食是一种罕见的饮食特化，在现存的脊椎动物中仅限于秃鹫。这些鸟类发挥着重要的生态服务作用，但许多秃鹫物种最近种群数量急剧下降，现已濒危。为了研究秃鹫中强制性食腐的分子适应机制，并评估基因组特征是否可能导致其种群数量下降，我们生成了喜马拉雅秃鹫和胡兀鹫的高质量基因组，它们分别代表了 Accipitridae 中独立起源的食腐行为，以及一个姐妹分类群，高山鹰。通过将我们的数据与其他鸟类的已发表序列进行比较，我们表明，秃鹫中强制性食腐行为的进化伴随着广泛的正选择作用于胃酸产生和免疫相关的基因。此外，我们还发现了平行分子进化的证据，这些食腐动物的不同分支之间存在氨基酸替换。我们的全基因组筛查还表明，喜马拉雅秃鹫和胡兀鹫的遗传多样性水平都很低，大约相当于其他鸟类基因组平均遗传多样性的一半。然而，种群重建表明，种群数量下降始于大约末次冰盛期，早于过去三十年有记录的急剧下降。总之，我们的基因组分析表明，秃鹫具有独特的处理腐肉的适应能力，但现代种群在遗传上是贫乏的，因此特别容易受到人为活动导致的进一步遗传侵蚀。
