The Key Laboratory of Conservation Biology for Endangered Wildlife of the Ministry of Education, State Conservation Center for Gene Resources of Endangered Wildlife, College of Life Sciences, Zhejiang University, Hangzhou, PR China.
PLoS One. 2013 Jul 19;8(7):e70229. doi: 10.1371/journal.pone.0070229. Print 2013.
Genetic variation plays a significant role in maintaining the evolutionary potential of a species. Comparing the patterns of adaptive and neutral diversity in extant populations is useful for understanding the local adaptations of a species. In this study, we determined the fine-scale genetic structure of 6 extant populations of the giant panda (Ailuropoda melanoleuca) using mtDNA and DNA fingerprints, and then overlaid adaptive variations in 6 functional Aime-MHC class II genes (DRA, DRB3, DQA1, DQA2, DQB1, and DQB2) on this framework. We found that: (1) analysis of the mtDNA and DNA fingerprint-based networks of the 6 populations identified the independent evolutionary histories of the 2 panda subspecies; (2) the basal (ancestral) branches of the fingerprint-based Sichuan-derived network all originated from the smallest Xiaoxiangling (XXL) population, suggesting the status of a glacial refuge in XXL; (3) the MHC variations among the tested populations showed that the XXL population exhibited extraordinary high levels of MHC diversity in allelic richness, which is consistent with the diversity characteristics of a glacial refuge; (4) the phylogenetic tree showed that the basal clades of giant panda DQB sequences were all occupied by XXL-specific sequences, providing evidence for the ancestor-resembling traits of XXL. Finally, we found that the giant panda had many more DQ alleles than DR alleles (33∶13), contrary to other mammals, and that the XXL refuge showed special characteristics in the DQB loci, with 7 DQB members of 9 XXL-unique alleles. Thus, this study identified XXL as a glacial refuge, specifically harboring the most number of primitive DQB alleles.
遗传变异在维持物种的进化潜力方面起着重要作用。比较现存种群中适应性和中性多样性的模式有助于了解物种的局部适应。在这项研究中，我们使用 mtDNA 和 DNA 指纹图谱确定了 6 个现存大熊猫（Ailuropoda melanoleuca）种群的精细遗传结构，然后在这个框架上叠加了 6 个功能性 Aim-MHC 类 II 基因（DRA、DRB3、DQA1、DQA2、DQB1 和 DQB2）的适应性变异。我们发现：（1）对 6 个种群的 mtDNA 和基于 DNA 指纹图谱的网络分析确定了 2 个熊猫亚种的独立进化历史；（2）基于指纹图谱的四川种群的基础（祖先）分支均源自最小的小相岭（XXL）种群，表明 XXL 是一个冰川避难所；（3）在测试的种群中，MHC 变异表明，XXL 种群在等位基因丰富度上表现出非凡的 MHC 多样性，这与冰川避难所的多样性特征一致；（4）系统发育树显示，大熊猫 DQB 序列的基础分支均由 XXL 特有的序列占据，为 XXL 的祖先相似特征提供了证据。最后，我们发现大熊猫的 DQ 等位基因比 DR 等位基因多（33∶13），与其他哺乳动物相反，而 XXL 避难所的 DQB 基因座具有特殊特征，在 9 个 XXL 独特等位基因中，有 7 个 DQB 成员。因此，本研究确定 XXL 是一个冰川避难所，特别拥有最多数量的原始 DQB 等位基因。
