Data from: Stronger spatial genetic structure in recolonized areas than in refugia in the European beech

Extant rear-edge populations located in former glacial refugia remain understudied despite their high conservation value. These populations should have experienced strong genetic drift due to their small size and long isolation. Moreover, the prolonged action of isolation-by-distance in refugial areas should result in stronger regional spatial genetic structure than in recolonized areas, but empirical tests of this prediction are scarce. To fill this gap, we first used a set of 16 microsatellite markers to investigate the genetic structure of European beech in France in 65 populations from three refugial areas and one control recolonized (non-refugial) area. Then, using the same approach, we reanalyzed published isozyme data from 375 populations distributed across the entire species range. We found stronger genetic differentiation among populations in refugia than in recolonized areas. However, contrary to expectations, regional spatial genetic structure was lower within refugia than within recolonized areas. Published studies presenting similar analyses suggest that our results could have generality across different biogeographical settings and types of organisms. Strong and prolonged genetic drift in refugial areas could have erased the signature of range expansions that is still visible in recolonized areas. Our results therefore suggest that Pleistocene population isolation has played a key role in increasing the genetic complexity of extant rear-edge populations.

尽管位于古冰期避难所（glacial refugia）的现存后缘种群（rear-edge populations）具有极高的保护价值，但相关研究长期未得到充分开展。由于种群规模狭小且长期隔离，这类种群往往经历了强烈的遗传漂变（genetic drift）。此外，避难所区域内长期持续的距离隔离（isolation-by-distance）效应，本应使其比再定居区域呈现出更强的区域空间遗传结构，但针对这一预测的实证检验仍较为匮乏。为填补这一研究空白，本研究首先借助16个微卫星标记（microsatellite markers），对法国境内的欧洲山毛榉开展遗传结构分析，样本涵盖3个避难所区域与1个对照再定居（非避难所）区域的共65个种群。随后，本研究采用相同方法，对已发表的、覆盖该物种全分布范围的375个种群的同工酶（isozyme）数据进行了重新分析。研究结果显示，避难所区域内种群间的遗传分化程度显著高于再定居区域。但与理论预期相悖的是，避难所区域内的区域空间遗传结构反而弱于再定居区域。已有同类分析的发表研究提示，本研究结果或可在不同生物地理背景与各类生物类群中具备普适性。避难所区域内强烈且长期持续的遗传漂变，或已抹去了种群范围扩张的遗传印记——这类印记在再定居区域中仍清晰可见。综上，本研究结果表明，更新世时期的种群隔离，在提升现存后缘种群的遗传复杂性方面发挥了关键作用。