Abstract：
\'Living fossils\', that is, ancient lineages of low taxonomic diversity, represent an exceptional evolutionary heritage, yet we know little about how demographic history and deleterious mutation load have affected their long-term survival and extinction risk. We performed whole-genome sequencing and population genomic analyses on Dipteronia sinensis and D. dyeriana, two East Asian Tertiary relict trees. We found large-scale genome reorganizations and identified species-specific genes under positive selection that are likely involved in adaptation. Our demographic analyses suggest that the wider-ranged D. sinensis repeatedly recovered from population bottlenecks over late Tertiary/Quaternary periods of adverse climate conditions, while the population size of the narrow-ranged D. dyeriana steadily decreased since the late Miocene, especially after the Last Glacial Maximum (LGM). We conclude that the efficient purging of deleterious mutations in D. sinensis facilitated its survival and repeated demographic recovery. By contrast, in D. dyeriana, increased genetic drift and reduced selection efficacy, due to recent severe population bottlenecks and a likely preponderance of vegetative propagation, resulted in fixation of strongly deleterious mutations, reduced fitness, and continuous population decline, with likely detrimental consequences for the species\' future viability and adaptive potential. Overall, our findings highlight the significant impact of demographic history on levels of accumulation and purging of putatively deleterious mutations that likely determine the long-term survival and extinction risk of Tertiary relict trees.
摘要：
\'活化石\',也就是说,古老的谱系分类多样性低，代表了一种特殊的进化遗产，然而，我们对人口统计学史和有害突变负荷如何影响其长期生存和灭绝风险知之甚少。我们进行了全基因组测序和群体基因组分析，两棵东亚第三纪遗留下来的树木。我们发现了大规模的基因组重组，并在正选择下鉴定了可能参与适应的物种特异性基因。我们的人口统计分析表明，在第三纪/第四纪后期不利气候条件下，范围更广的D.sinensis从人口瓶颈中反复恢复。而窄范围的D.dyeriana的种群规模自晚以来稳步下降，尤其是在最后一次冰川最大值（LGM）之后。我们得出的结论是，有效清除中华绒螯蟹中的有害突变有助于其生存和反复的人口恢复。相比之下,在D.dyeriana，增加遗传漂移和降低选择效力，由于最近严重的人口瓶颈和营养繁殖的可能优势，导致强烈有害突变的固定，健身减少,人口持续下降，可能对物种未来的生存能力和适应潜力产生不利影响。总的来说,我们的研究结果强调了人口统计学史对推定有害突变的积累和清除水平的显著影响,这些突变可能决定了第三纪残存树木的长期存活和灭绝风险.
