Data from: Range-edge genetic diversity: locally poor extant southern patches maintain a regionally diverse hotspot in the seagrass Zostera marina

Refugial populations at the rear edge are predicted to contain higher genetic diversity than those resulting from expansion, such as in post-glacial recolonizations. However, peripheral populations are also predicted to have decreased diversity compared to the center of a species’ distribution. We aim to test these predictions by comparing genetic diversity in populations at the limits of distribution of the seagrass Zostera marina, with populations in the species' previously described central diversity 'hotspot'. Zostera marina populations show decreased allelic richness, heterozygosity and genotypic richness in both the 'rear' edge and the 'leading' edge compared to the diversity 'hotspot' in the North Sea / Baltic region. However, when populations are pooled, genetic diversity at the southern range is as high as in the North Sea / Baltic region while the 'leading edge' remains low in genetic diversity. The decreased genetic diversity in these Southern Iberia populations compared to more central populations is possibly the effect of drift due to small effective population size, as a result of reduced habitat, low sexual reproduction and low gene flow. However, when considering the whole southern edge of distribution rather than per population, diversity is as high as in the central 'hotspot' in the North Sea / Baltic region. We conclude that diversity patterns assessed per population can mask the real regional richness that is typical of rear edge populations, which have played a key role in the species biogeographic history and as marginal diversity hotspots have very high conservation value.

学界普遍预测，物种分布后缘的避难所种群（refugial population）所拥有的遗传多样性，要高于诸如冰期后重新拓殖这类由种群扩张形成的种群。不过，相较于物种分布区的核心种群，边缘种群的遗传多样性也被预测会有所降低。本研究旨在通过对比大叶藻（Zostera marina）分布极限处的种群与该物种此前已被报道的核心遗传多样性热点区域的种群，来验证上述两项预测。相较于北海-波罗的海区域的多样性热点种群，大叶藻在‘后缘’与‘前缘’分布区的种群均表现出等位基因丰富度、杂合度以及基因型丰富度的下降。不过，若将种群合并统计，南部分布区的遗传多样性水平与北海-波罗的海区域相当，而‘前缘’分布区的遗传多样性仍处于较低水平。相较于核心区域种群，伊比利亚南部种群的遗传多样性下降，可能是由于生境缩减、有性繁殖率低以及基因交流匮乏导致有效种群规模过小，进而引发遗传漂变所致。但如果从整个南部分布边缘而非单一种群的层面考量，其多样性水平与北海-波罗的海区域的核心热点区域并无显著差异。本研究得出结论：仅基于单一种群评估的多样性模式，可能会掩盖后缘种群所特有的真实区域多样性水平。后缘种群在物种生物地理历史中发挥了关键作用，且作为边缘多样性热点区域，具备极高的保护价值。