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.

分布后缘的避难所种群，其遗传多样性被预测高于冰期后重新拓殖等扩张过程形成的种群。不过，相较于物种分布的核心区域，边缘种群的遗传多样性同样会出现下降。本研究旨在通过对比海草大叶藻（Zostera marina）分布极限处的种群与该物种此前被报道的核心多样性“热点”区域的种群遗传多样性，验证上述两项预测。结果显示，相较于北海-波罗的海区域的多样性“热点”，大叶藻的后缘与前缘种群的等位基因丰富度、杂合度以及基因型丰富度均有所下降。但将种群合并分析后发现，南部分布区的遗传多样性水平与北海-波罗的海区域相当，而前缘种群的遗传多样性依旧处于较低水平。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，可能是由于栖息地缩减、有性繁殖水平低下以及基因交流匮乏导致有效种群规模偏小，进而引发遗传漂变所致。但若从整个分布南缘而非单一种群的层面考量，其多样性水平与北海-波罗的海的核心“热点”区域并无显著差异。本研究得出结论：单一种群尺度下的多样性格局，可能会掩盖分布后缘种群真实的区域丰富度特征——这类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，其保护价值极高。