Armstrong Matthew R, Wilson Robert E, Johnson James A, Booms Travis L, Gesmundo Callie F, Pohlen Zachary M, Leonard Paul B, Sonsthagen Sarah A
School of Natural Resources University of Nebraska Lincoln Lincoln Nebraska USA.
Nebraska State Museum University of Nebraska Lincoln Lincoln Nebraska USA.
Ecol Evol. 2025 Jun 26;15(7):e71673. doi: 10.1002/ece3.71673. eCollection 2025 Jul.
Hybridization is a common process among bird species that can precipitate a mix of positive or negative species outcomes. Particularly for rare populations, detrimental effects of hybridization on demographic growth rates and genetic integrity are of serious concern. In Alaska and a small region of northwestern Canada, the endemic subspecies of Gray-headed Chickadee () has declined in recent decades from being locally common to being extremely rare. The more widespread Boreal Chickadee () has become increasingly abundant in areas of sympatry. These changes in abundance may have led to hybridization between Gray-headed Chickadees and Boreal Chickadees. We used a series of analyses to test for signatures of introgression at mitochondrial DNA and nuclear DNA using historical museum samples of both species collected between 1875 and 1979 as well as contemporary Boreal Chickadee samples. In addition, we modeled Gray-headed Chickadee and Boreal Chickadee demographic histories to better understand patterns of effective population size changes and gene flow over time. Introgression of Gray-headed Chickadee nuclear DNA was detected in contemporary and historical Boreal Chickadee populations, and two first-generation hybrid backcrosses were observed in the historical Boreal Chickadee samples. Lack of mitochondrial DNA introgression or backcrossing into the Gray-headed Chickadee historical samples may be an artifact of mate scarcity during the period before local abundances of Boreal Chickadee exceeded Gray-headed Chickadees. Demographic modeling with nuclear loci estimated a low level of symmetric gene flow between Gray-headed Chickadees and Boreal Chickadees since the time of divergence. Our study suggests that hybridization may be linked to Gray-headed Chickadee declines and represents a case study of how museum collections can be used to infer introgression in a population too scarce to directly investigate.
杂交是鸟类物种中常见的过程，可能会引发一系列积极或消极的物种结果。特别是对于珍稀种群而言，杂交对种群增长率和遗传完整性的不利影响备受关注。在阿拉斯加和加拿大西北部的一小片区域，黑头山雀（）的特有亚种在近几十年间，已从原本在当地较为常见变得极为稀少。分布更广的黑顶山雀（）在同域分布地区的数量却日益增多。这些数量上的变化可能导致了黑头山雀和黑顶山雀之间的杂交。我们使用了一系列分析方法，利用1875年至1979年间收集的这两个物种的历史博物馆样本以及当代黑顶山雀样本，来检测线粒体DNA和核DNA的基因渗入特征。此外，我们还对黑头山雀和黑顶山雀的种群历史进行了建模，以更好地了解有效种群大小随时间的变化模式和基因流动情况。在当代和历史黑顶山雀种群中均检测到了黑头山雀核DNA的基因渗入现象，并且在历史黑顶山雀样本中观察到了两个第一代杂交回交个体。在黑头山雀历史样本中未检测到线粒体DNA的基因渗入或回交现象，这可能是由于在当地黑顶山雀数量超过黑头山雀之前的那段时间里，配偶稀缺所致。利用核基因座进行的种群动态建模估计，自分化以来，黑头山雀和黑顶山雀之间存在低水平的对称基因流动。我们的研究表明，杂交可能与黑头山雀数量的减少有关，并且代表了一个利用博物馆藏品来推断过于稀少而无法直接研究的种群中的基因渗入情况的案例研究。
