Fine-scale genetic structure reflects limited and coordinated dispersal in the colonial monk parakeet, Myiopsitta monachus

The genetic structure of animal populations has considerable behavioural, ecological and evolutionary implications and may arise from various demographic traits. Here, we use observational field data and molecular genetics to determine the genetic structure of an invasive population of monk parakeets, Myiopsitta monachus, at a range of spatial scales, and investigate the demographic processes that generate the observed structure. Monk parakeets construct large nests that can house several pairs occupying separate chambers; these nests are often aggregated within nesting trees. We determined patterns of relatedness within compound nests, within nesting trees and between trees. Spatial autocorrelation analyses of pairwise genetic relatedness revealed fine-scale genetic structure with relatives of both sexes spatially clustered within, but not beyond, nesting trees. In addition, males were more related to males sharing their compound nests than to other males occupying the same nesting tree. By contrast, males and females within compound nests were not significantly more closely related than elsewhere in the same tree, and we found no evidence for inbreeding. Adults showed high breeding site fidelity between years despite considerable disturbance of nest sites. Natal dispersal was female-biased, but dispersal distances were relatively short with some natal philopatry observed in both sexes. Sibling coalitions, typically of males, were observed amongst both philopatric and dispersing birds. Our results show significant clustering of kin within compound nests and nesting trees resulting from limited and coordinated natal dispersal, with subsequent breeding site fidelity. The resulting genetic structure has implications for social behaviour in this unusual parrot species.

动物种群的遗传结构（genetic structure）具有显著的行为、生态与进化意义，其形成可源于多种种群统计特征。本研究借助野外观测数据与分子遗传学（molecular genetics）手段，在多个空间尺度上解析了和尚鹦鹉（Myiopsitta monachus）入侵种群（invasive population）的遗传结构，并探究了塑造该观测结构的种群统计过程。

和尚鹦鹉可构筑大型复合巢，每巢可容纳多对占据独立巢室的个体；这类巢穴常聚集于同一营巢树内。我们分别分析了复合巢内、营巢树内以及不同营巢树间的亲缘关系（relatedness）模式。对成对遗传亲缘关系开展的空间自相关分析（spatial autocorrelation analyses）显示，该种群存在精细尺度的遗传结构：雌雄两性的亲属个体均在营巢树内部呈现空间聚集，但在营巢树范围之外则无此聚集特征。此外，共享同一复合巢的雄性个体之间，其亲缘关系相较于共享同一营巢树的其他雄性更为紧密。与之相反，复合巢内的雄性与雌性个体间的亲缘关系，并未显著高于同一营巢树内其他个体间的亲缘水平，且未发现近交（inbreeding）的相关证据。

尽管营巢位点常遭受显著干扰，成体个体仍表现出较高的年度繁殖位点忠实性（breeding site fidelity）。出生扩散（natal dispersal）呈雌性偏倚特征，但扩散距离相对较短，且两性均观察到一定程度的出生留居（natal philopatry）现象。研究还发现了通常由雄性组成的同胞联盟（sibling coalitions），此类联盟既存在于留居个体中，也见于扩散个体中。

本研究结果表明，有限且协同的出生扩散结合后续的繁殖位点忠实性，使得亲属个体在复合巢与营巢树内出现显著聚集。由此形成的遗传结构，对这一特殊鹦鹉类群的社会行为具有重要影响。