Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China.
PLoS One. 2012;7(1):e30423. doi: 10.1371/journal.pone.0030423. Epub 2012 Jan 17.
To further extend our understanding of the mechanism causing the current nearly extinct status of the baiji (Lipotes vexillifer), one of the most critically endangered species in the world, genetic diversity at the major histocompatibility complex (MHC) class II DRB locus was investigated in the baiji. Nine highly divergent DRB alleles were identified in 17 samples, with an average of 28.4 (13.2%) nucleotide difference and 16.7 (23.5%) amino acid difference between alleles. The unexpectedly high levels of DRB allelic diversity in the baiji may partly be attributable to its evolutionary adaptations to the freshwater environment which is regarded to have a higher parasite diversity compared to the marine environment. In addition, balancing selection was found to be the main mechanisms in generating sequence diversity at baiji DRB gene. Considerable sequence variation at the adaptive MHC genes despite of significant loss of neutral genetic variation in baiji genome might suggest that intense selection has overpowered random genetic drift as the main evolutionary forces, which further suggested that the critically endangered or nearly extinct status of the baiji is not an outcome of genetic collapse.
为了进一步深入了解导致白鱀豚（Lipotes vexillifer）这种全球最濒危物种之一近乎灭绝的机制，我们对其主要组织相容性复合体（MHC）II 类 DRB 基因座的遗传多样性进行了研究。在 17 个样本中鉴定出了 9 个高度分化的 DRB 等位基因，等位基因之间的平均核苷酸差异为 28.4%（13.2%），平均氨基酸差异为 16.7%（23.5%）。白鱀豚 DRB 基因的高度多样化可能部分归因于其对淡水环境的进化适应，与海洋环境相比，淡水环境中的寄生虫多样性更高。此外，平衡选择被认为是产生白鱀豚 DRB 基因序列多样性的主要机制。尽管白鱀豚基因组中性遗传变异显著丧失，但适应性 MHC 基因仍存在大量序列变异，这表明强烈的选择已经超过了随机遗传漂变成为主要的进化力量，这进一步表明，白鱀豚的极度濒危或近乎灭绝状态不是遗传崩溃的结果。
