Data from: Variation in fine-scale genetic structure and local dispersal patterns between peripheral populations of a South American passerine bird

The distribution of suitable habitat influences natal and breeding
dispersal at small spatial scales, resulting in strong micro-geographic
genetic structure. Although environmental variation can promote
inter-population differences in dispersal behavior and local spatial
patterns, the effects of distinct ecological conditions on within-species
variation in dispersal strategies and in fine-scale genetic structure
remain poorly understood. We studied local dispersal and fine-scale
genetic structure in the thorn-tailed rayadito (Aphrastura spinicauda), a
South American bird that breeds along a wide latitudinal gradient. We
combine capture-mark-recapture data from eight breeding seasons and
molecular genetics to compare two peripheral populations with contrasting
environments in Chile: Navarino Island, a continuous and low density
habitat, and Fray Jorge National Park, a fragmented, densely populated and
more stressful environment. Natal dispersal showed no sex bias in
Navarino, but was female-biased in the more dense population in Fray
Jorge. In the latter, male movements were restricted and some birds seemed
to skip breeding in their first year, suggesting habitat saturation.
Breeding dispersal was limited in both populations, with males being more
philopatric than females. Spatial genetic autocorrelation analyses using
13 polymorphic microsatellite loci confirmed the observed dispersal
patterns: a fine-scale genetic structure was only detectable for males in
Fray Jorge for distances up to 450 m. Furthermore, two-dimensional
autocorrelation analyses and estimates of genetic relatedness indicated
that related males tended to be spatially clustered in this population.
Our study shows evidence for context-dependent variation in natal
dispersal and corresponding local genetic structure in peripheral
populations of this bird. It seems likely that the costs of dispersal are
higher in the fragmented and higher density environment in Fray Jorge,
particularly for males. The observed differences in micro-geographic
genetic structure for rayaditos might reflect the genetic consequences of
population-specific responses to contrasting environmental pressures near
the range limits of its distribution.

适宜栖息地的分布会在小空间尺度上调控出生扩散（natal dispersal）与繁殖扩散（breeding dispersal），进而塑造显著的微地理遗传结构（micro-geographic genetic structure）。尽管环境变异可推动不同种群间扩散行为与局域空间格局产生分化，但独特生态条件对物种内扩散策略及精细尺度遗传结构的种内变异的影响机制，目前仍未得到充分解析。本研究以南美洲鸟类尖尾树雀（Aphrastura spinicauda）为研究对象，该物种沿宽阔纬度梯度开展繁殖活动。我们结合8个繁殖季的标记重捕（capture-mark-recapture）数据与分子遗传学手段，对比了智利境内两个环境迥异的边缘种群：纳瓦里诺岛（Navarino Island）——其栖息地连续且种群密度较低，以及弗雷霍雷国家公园（Fray Jorge National Park）——该区域栖息地破碎化、种群密度更高且环境胁迫更强。研究结果显示，纳瓦里诺岛种群的出生扩散未表现出性别偏倚，而在密度更高的弗雷霍雷种群中，出生扩散呈现雌性偏倚特征；在后一种群内，雄性的移动受到显著限制，部分个体甚至会在首个繁殖季跳过繁殖，这暗示该种群存在栖息地饱和现象。两种群的繁殖扩散均较为有限，且雄性比雌性更具恋巢性（philopatric）。基于13个多态性微卫星（microsatellite）位点开展的空间遗传自相关分析（spatial genetic autocorrelation analyses）验证了上述扩散模式：仅在弗雷霍雷种群的雄性个体中，在450米以内的距离尺度上可检测到精细尺度的遗传结构。此外，二维自相关分析与遗传亲缘关系（genetic relatedness）估计结果表明，该种群内亲缘关系较近的雄性个体倾向于在空间上形成聚集分布。本研究证实了该鸟类边缘种群中出生扩散的情境依赖性变异，以及与之对应的局域遗传结构。相较于纳瓦里诺岛种群，弗雷霍雷破碎化且高密度的生境中扩散成本更高，这一现象在雄性个体中尤为突出。尖尾树雀所观测到的微地理遗传结构差异，可能反映了该物种在分布范围边缘处，针对不同环境压力产生的种群特异性响应所带来的遗传后果。