Non-Invasive Genetic Monitoring of Wild Central Chimpanzees

BackgroundAn assessment of population size and structure is an important first step in devising conservation and management plans for endangered species. Many threatened animals are elusive, rare and live in habitats that prohibit directly counting individuals. For example, a well-founded estimate of the number of great apes currently living in the wild is lacking. Developing methods to obtain accurate population estimates for these species is a priority for their conservation management. Genotyping non-invasively collected faecal samples is an effective way of evaluating a species' population size without disruption, and can also reveal details concerning population structure.Methodology/Principal FindingsWe opportunistically collected wild chimpanzee faecal samples for genetic capture-recapture analyses over a four-year period in a 132 km2 area of Loango National Park, Gabon. Of the 444 samples, 46% yielded sufficient quantities of DNA for genotyping analysis and the consequent identification of 121 individuals. Using genetic capture-recapture, we estimate that 283 chimpanzees (range: 208–316) inhabited the research area between February 2005 and July 2008. Since chimpanzee males are patrilocal and territorial, we genotyped samples from males using variable Y-chromosome microsatellite markers and could infer that seven chimpanzee groups are present in the area. Genetic information, in combination with field data, also suggested the occurrence of repeated cases of intergroup violence and a probable group extinction.Conclusions/SignificanceThe poor amplification success rate resulted in a limited number of recaptures and hence only moderate precision (38%, measured as the entire width of the 95% confidence interval), but this was still similar to the best results obtained using intensive nest count surveys of apes (40% to 63%). Genetic capture-recapture methods applied to apes can provide a considerable amount of novel information on chimpanzee population size and structure with minimal disturbance to the animals and represent a powerful complement to traditional field-based methods.**背景**：对种群数量与结构进行评估，是制定濒危物种保护与管理方案的首要关键步骤。诸多受胁动物行踪诡秘、种群稀少，且栖息环境特殊，难以直接开展个体计数工作。例如，目前尚无针对野生现存类人猿种群数量的可靠估算结果。研发可精准获取这类物种种群估算数据的方法，是其保护管理工作的重中之重。对非侵入性采集的粪便样本进行基因分型（genotyping），是在不干扰动物的前提下评估物种种群规模的有效手段，同时还可揭示种群结构的相关细节。 **方法与主要结果**：研究团队在加蓬洛安戈国家公园132平方千米的研究区域内，耗时四年机遇性采集野生黑猩猩粪便样本，用于遗传标记重捕法（genetic capture-recapture）分析。在444份粪便样本中，46%的样本提取到了足量用于基因分型分析的DNA，由此成功鉴定出121只个体。借助遗传标记重捕法，我们估算得出：2005年2月至2008年7月期间，该研究区域内栖息着283只黑猩猩（置信区间：208~316）。由于黑猩猩雄性为父系定居且具有领地性，研究团队利用多态性Y染色体微卫星标记（Y-chromosome microsatellite markers）对雄性个体样本进行基因分型，由此推断该区域内存在7个黑猩猩社群。结合野外调查数据的遗传信息还显示，该区域曾多次发生社群间暴力冲突，且存在一个社群疑似灭绝的情况。 **结论与意义**：本次研究的DNA扩增成功率较低，导致重捕个体数量有限，因此估算精度中等（95%置信区间（95% confidence interval）全宽为38%），但该结果仍与采用类人猿密集巢计数调查法得到的最佳结果（40%~63%）相当。针对类人猿开展的遗传标记重捕法，可在尽可能减少对动物干扰的前提下，获取大量关于黑猩猩种群规模与结构的全新信息，是对传统野外调查方法的有力补充。