Winter connectivity and leapfrog migration in a migratory passerine

Aim: Every year birds prepare for their migration journey, and understanding how this phenomenon is carried out allows us to infer whether human activities have influenced and modified the way in which the birds migrate. Many bird species perform long-distance movements to find sites with better conditions and optimize the use of resources during the annual cycle. These migration movements in birds have been studied using different methods, from mist nets, mark and recapture techniques, geolocators to document movements, and stable hydrogen isotopes. In this study, we used a genetic tool to create a graphic representation of the genetic variation across the species breeding range or genoscape as a reference to assess the connectivity of a migratory bird across its annual cycle. The advantage of the genoscape approach is that it allows us to identify distinct genetic units in the breeding range and then detect the migration pattern of those units through time and space. Methods: We studied migration in the Painted Bunting (Passerina ciris) using genetic data from 386 individuals across the breeding range, 230 samples from 28 migration stopover locations, and 178 samples from 16 wintering locations. We also combined population and individual-level genetic assignments to breeding areas in order to study migratory connectivity patterns in greater depth. Results: Our results show the existence of four main genetic groups within the species: Eastern, Southwestern, Central, and Louisiana. We also found that most of the individuals migrate during the fall towards Western Mexico and Central America and return to their breeding sites through the coastal plains of the Gulf of Mexico; the Louisiana breeding unit migrates to the Yucatan Peninsula and Central America, returning to their breeding sites in the spring through the coastal plains of the Gulf of Mexico. We found strong support for the existence of a Leap-frog migration pattern. Main conclusions: We use a genoscape approach to investigate population structure and broad-scale migration patterns in the Painted Bunting. By screening samples from across the annual cycle, we can reveal clear patterns of population structure across the breeding range and provide strong support for the existence of leapfrog migration.

【研究目的】鸟类每年都会为迁徙旅程做准备，阐明这一迁徙现象的发生机制，有助于我们推断人类活动是否对鸟类的迁徙方式产生了影响与改变。诸多鸟类物种会进行长距离移动，以寻找环境更适宜的区域，并在年度生活周期中优化资源利用。此前针对鸟类迁徙行为的研究已采用了多种方法，包括雾网、标记重捕技术、用于记录移动轨迹的地理定位器，以及稳定氢同位素分析。本研究借助遗传工具，绘制了该物种繁殖分布区内的遗传变异可视化图谱，即基因景观（genoscape），以此作为参考来评估迁徙鸟类在整个年度周期中的迁徙连通性。基因景观分析方法的优势在于，能够帮助研究者在繁殖分布区内识别出不同的遗传单元，进而追踪这些遗传单元随时间与空间变化的迁徙模式。【研究方法】本研究以彩鹀（Passerina ciris）为研究对象，使用了三类遗传数据：覆盖其繁殖分布区的386个个体的遗传数据、来自28个迁徙停歇地的230份样本数据，以及来自16个越冬地的178份样本数据。同时，本研究结合种群水平与个体水平的繁殖区遗传归属分析，以更深入地探究其迁徙连通性模式。【研究结果】本研究结果显示，彩鹀种群内存在四个主要遗传类群：东部类群、西南部类群、中部类群以及路易斯安那类群。同时发现，绝大多数个体在秋季向墨西哥西部与中美洲迁徙，并在春季通过墨西哥湾沿岸平原返回繁殖地；而路易斯安那繁殖类群则会迁徙至尤卡坦半岛与中美洲，同样在春季经由墨西哥湾沿岸平原返回其繁殖区。本研究为跳跃式迁徙（leap-frog migration）模式的存在提供了强有力的证据支持。【主要结论】本研究通过基因景观（genoscape）分析方法，探究了彩鹀的种群结构与大范围迁徙模式。通过对覆盖其年度生活周期的各类样本进行分析，本研究清晰揭示了其繁殖分布区内的种群结构模式，并为跳跃式迁徙模式的存在提供了强有力的支撑。