Genotypes for yardstick population from the Nakai Plateau, Lao PDR at 25 loci

Conservation biologists often deal with species that have small, fragmented populations throughout their range, making it necessary to prioritize populations for management. Genetics provides tools to assist with prioritization according to the levels and distribution of genetic diversity and evolutionary distinctiveness. Many studies have used nuclear microsatellite loci to measure genetic diversity in disparate populations and mitochondrial DNA to assess genetic distinctiveness. However, comparing metrics based on microsatellite genotypes ascertained in different laboratories is complicated by the selection of different loci with distinct nucleotide repeat motifs. This issue may be resolved by comparing metrics to a well-characterized reference population with shared microsatellite markers. The Asian elephant, Elephas maximus, is an endangered species with 50–60% of populations in India and Sri Lanka, and small, fragmented populations throughout southeast and insular Asia. We assessed range-wide genetic diversity of the Asian elephant by directly comparing allelic diversity and heterozygosity estimates from 35 populations, overcoming marker selection bias by calibrating metrics to a large population on the Nakai Plateau, Lao PDR, genotyped at 25 loci. We coupled these results with mtDNA analysis to evaluate genetic distinctiveness and identify potential conservation management units. We found the greatest diversity in the populations of southeast Asia and the greatest genetic distinctiveness among the subspecies designations, particularly Borneo and Sumatra, and other southeast Asian populations. The populations of southeast Asia, albeit small, fragmented, and at high risk of extirpation, contain valuable diversity and distinctiveness and are thus of high priority for the preservation of the Asian elephant.

保护生物学家通常需要应对分布范围内种群规模狭小且碎片化的物种种群，因此有必要为不同种群制定管理优先级。遗传学可提供相关工具，依据遗传多样性水平与分布特征、进化独特性来辅助开展优先级排序工作。既往诸多研究均采用核微卫星位点（nuclear microsatellite loci）来衡量不同种群的遗传多样性，并借助线粒体DNA（mitochondrial DNA）评估进化独特性。然而，由于不同实验室选用的核苷酸重复基序各异的位点存在差异，基于不同实验室获得的微卫星基因型所计算的统计指标，其跨实验室可比性往往受到极大限制。若将统计指标与采用共享微卫星标记的标准化参考种群进行校准，则可解决该问题。亚洲象（Elephas maximus）属于濒危物种，全球50%至60%的种群分布于印度与斯里兰卡，其余零散且碎片化的种群则遍布东南亚及亚洲群岛区域。本研究通过直接对比35个种群的等位基因多样性与杂合度估算值，对亚洲象的全分布区遗传多样性展开评估；同时以老挝人民民主共和国（Lao PDR）Nakai高原的一个大型种群为校准基准（该种群已完成25个位点的基因分型），以此克服标记选择偏倚带来的影响。本研究结合上述结果与mtDNA分析，对进化独特性进行评估，并确定潜在的保护管理单元。研究结果显示，东南亚种群的遗传多样性最高，而在各亚种划分中（尤其是婆罗洲与苏门答腊亚种）以及其他东南亚种群间，进化独特性最为显著。尽管东南亚种群规模狭小、结构碎片化且面临极高的局部灭绝风险，但其蕴含着极具价值的遗传多样性与进化独特性，因此在亚洲象物种保护工作中应被列为最高优先级的保护对象。