Department of Animal Science, University of California, Davis, California, USA.
Department of Evolution and Ecology, University of California, Davis, California, USA.
Mol Ecol. 2022 Sep;31(17):4544-4557. doi: 10.1111/mec.16592. Epub 2022 Jul 21.
Range expansions-whether permanent or transient-strongly influence the distribution of genetic variation in space. Monarch butterflies are best known for long-distance seasonal migration within North America but are also established as nonmigratory populations around the world, including on Pacific Islands. Previous research has highlighted stepwise expansion across the Pacific, though questions remain about expansion timing and the population genetic consequences of migration loss. Here, we present reduced-representation sequencing data for 275 monarchs from North America (n = 85), 12 Pacific Islands (n = 136) and three locations in Australia (n = 54), with the goal of understanding (i) how the monarch's Pacific expansion has shaped patterns of population genetic variation and (ii) how loss of migration has influenced spatial patterns of differentiation. We find support for previously described stepwise dispersal across the Pacific and document an additional expansion from Hawaii into the Mariana Islands. Nonmigratory monarchs within the Mariana Islands show strong patterns of differentiation, despite their proximity; by contrast, migratory North American samples form a single genetically panmictic population across the continent. Estimates of Pacific establishment timing are highly uncertain (~100-1,000,000 years ago) but overlap with historical records that indicate a recent expansion. Our data support (i) a recent expansion across the Pacific whose timing overlaps with available historical records of establishment and (ii) a strong role for seasonal migration in determining patterns of spatial genetic variation. Our results are noteworthy because they demonstrate how the evolution of partial migration can drive population differentiation over contemporary timescales.
范围扩展——无论是永久性的还是暂时性的——都会强烈影响遗传变异在空间中的分布。帝王蝶以其在北美的长途季节性迁徙而闻名，但它们也在世界各地建立了非迁徙种群，包括太平洋岛屿上。以前的研究强调了跨越太平洋的逐步扩张，尽管关于扩张时间和迁徙损失对种群遗传的影响仍存在一些问题。在这里，我们为来自北美的 275 只帝王蝶（n=85）、12 个太平洋岛屿（n=136）和澳大利亚的三个地点（n=54）提供了简化代表性测序数据，目的是了解：(i) 帝王蝶在太平洋的扩张如何塑造了种群遗传变异模式；(ii) 迁徙损失如何影响分化的空间模式。我们支持以前描述的跨越太平洋的逐步扩散，并记录了从夏威夷到马里亚纳群岛的额外扩张。马里亚纳群岛内的非迁徙帝王蝶尽管彼此接近，但表现出强烈的分化模式；相比之下，迁徙的北美样本在整个大陆形成了一个单一的遗传混合种群。对太平洋建立时间的估计非常不确定（~100-100 万年前），但与表明最近扩张的历史记录重叠。我们的数据支持：(i) 最近跨越太平洋的扩张，其时间与现有的建立历史记录重叠；(ii) 季节性迁徙在决定空间遗传变异模式方面的重要作用。我们的研究结果值得注意，因为它们展示了部分迁徙的进化如何在当代时间尺度上推动种群分化。
