Data from: Serial founder effects and genetic differentiation during worldwide range expansion of monarch butterflies

Range expansions can result in founder effects, increasing genetic differentiation between expanding populations and reducing genetic diversity along the expansion front. However, few studies have addressed these effects in long-distance migratory species, for which high dispersal ability might counter the effects of genetic drift. Monarchs (Danaus plexippus) are best known for undertaking a long-distance annual migration in North America, but have also dispersed around the world to form populations that do not migrate or travel only short distances. Here, we used microsatellite markers to assess genetic differentiation among 18 monarch populations and to determine worldwide colonization routes. Our results indicate that North American monarch populations connected by land show limited differentiation, probably because of the monarch's ability to migrate long distances. Conversely, we found high genetic differentiation between populations separated by large bodies of water. Moreover, we show evidence for serial founder effects across the Pacific, suggesting stepwise dispersal from a North American origin. These findings demonstrate that genetic drift played a major role in shaping allele frequencies and created genetic differentiation among newly formed populations. Thus, range expansion can give rise to genetic differentiation and declines in genetic diversity, even in highly mobile species.

种群范围扩张可引发奠基者效应（founder effect），加剧扩张种群间的遗传分化，并沿扩张前沿降低遗传多样性。然而，鲜有研究针对长距离迁徙物种探讨此类效应——这类物种凭借强大的扩散能力，或可抵消遗传漂变（genetic drift）的影响。帝王蝶（Danaus plexippus）以其在北美开展的长距离年度迁徙而闻名，但它们也已扩散至全球各地，形成了不迁徙或仅进行短距离移动的种群。本研究利用微卫星标记（microsatellite marker），对18个帝王蝶种群间的遗传分化进行评估，并解析全球定殖路径。研究结果显示，通过陆地相连的北美帝王蝶种群间遗传分化程度有限，这大概率源于帝王蝶的长距离迁徙能力；反之，被大片水域阻隔的种群间则呈现出显著的遗传分化。此外，我们在跨太平洋区域发现了连续奠基者效应（serial founder effect）的相关证据，表明帝王蝶种群起源于北美，并通过逐步扩散的方式拓展至全球。这些研究结果表明，遗传漂变在塑造等位基因频率（allele frequency）以及在新形成的种群间催生遗传分化方面发挥了关键作用。由此可见，即便在移动能力极强的物种中，种群范围扩张同样可引发遗传分化与遗传多样性的降低。