Estimation of breeding population size using DNA-based pedigree reconstruction in brown bears

Robust estimates of demographic parameters are critical for effective wildlife conservation and management, but are difficult to obtain for elusive species. We estimated the breeding and adult population sizes, as well as the minimum population size, in a high-density brown bear population on the Shiretoko Peninsula, in Hokkaido, Japan, using DNA-based pedigree reconstruction. A total of 1,288 individuals, collected in and around the Shiretoko Peninsula between 1998 and 2020, were genotyped at 21 microsatellite loci. Among them, 499 individuals were identified by intensive genetic sampling conducted in two consecutive years (2019 and 2020) mainly by noninvasive methods (e.g., hair and fecal DNA). Among them, both parents were assigned for 330 bears, and either maternity or paternity was assigned to 47 and 76 individuals, respectively. The subsequent pedigree reconstruction indicated a range of breeding and adult (≥4 years old) population sizes: 128–173 for female breeders and 66–91 male breeders, and 155–200 for female adults and 84–109 male adults. The minimum population size was estimated to be 449 (252 females and 197 males) in 2019. Long-term continuous genetic sampling prior to a short-term intensive survey would enable parentage to be identified in a population with a high probability, thus enabling reliable estimates of breeding population size for elusive species. --种群参数的稳健估计是开展高效野生动物保护与管理的关键，但针对隐匿性物种而言，此类估计往往难以获取。我们依托基于DNA的谱系重建（pedigree reconstruction）技术，对日本北海道知床半岛的高密度棕熊种群，开展了繁殖种群规模、成年种群规模及最小种群规模的估算。本研究于1998年至2020年间，在知床半岛及其周边区域共收集1288只个体的样本，并对其21个微卫星位点（microsatellite loci）完成基因分型。其中，通过2019年与2020年连续两年开展的高强度遗传采样（主要采用毛发、粪便DNA等非侵入式方法（noninvasive methods）），共鉴定出499只个体。在上述499只个体中，330只可确定双亲身份，另有47只仅鉴定出母本、76只仅鉴定出父本。后续的谱系重建分析结果显示，繁殖种群与成年（≥4岁）种群的规模区间如下：雌性繁殖个体128~173只，雄性繁殖个体66~91只；雌性成年个体155~200只，雄性成年个体84~109只。2019年的最小种群规模估算值为449只，其中雌性252只、雄性197只。研究表明，在短期高强度采样前开展长期连续的遗传采样，可大幅提升种群内亲权鉴定的概率，进而为隐匿性物种提供可靠的繁殖种群规模估算结果。