天鹅洲迁地保护江豚种群近亲繁殖状况评估

长江江豚(Neophocaena asiaeorientalis asiaeorientalis)已处于极度濒危状况,迁地保护被认为是避免其灭绝最有希望的保护措施。本文选用21个多态性微卫星标记对2010年10月天鹅洲迁地保护江豚种群进行了亲子鉴定和亲缘关系分析,以检测该种群的近亲繁殖状况,为种群管理提供参考信息。本研究从18个体中检测到3个父-母-子家庭,以及母子和父子各1对。由于检测到的亲子关系较少,单从亲子鉴定结果不能判断该种群是否存在近亲繁殖。然而,亲缘关系分析结果表明,该迁地保护江豚种群的平均亲缘系数r为0.118 2,候选亲本间亲缘系数r为0.115 2,均显著高于长江江豚自然种群。而且,天鹅洲迁地保护江豚种群中具有亲缘关系的个体对达26.14%,高于自然种群6倍以上。此外,该种群的近交系数(Fis)为0.046。基于亲缘系数和近交系数的分析结果均表明,该种群存在较高的近交风险或者可能已经发生近交。本研究建议将种群中亲缘关系最多的雌性F34和雄性M45移出,并以每代(约5年)按雌雄1∶1的比例引进2头可繁殖个体,以降低近亲繁殖风险。此外,建议尽快为该迁地保护江豚种群构建遗传谱系,以便今后开展种群遗传管理。

Inbreeding Evaluation on the Ex Situ Conserved Yangtze Finless Porpoise Population in Tian'eZhou National Natural Reserve

The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is a unique freshwater subspecies of Neophocaena asiaeorientalis, which is endemic to the Yangtze River of China and is now critically endangered. Because its natural habitat is not expected to improve in near future, ex situ conservation was considered as the most important strategy to prevent it from distinction. However, in theory, without effective human intervention, inbreeding is unavoidable for any ex situ conserved small population. To evaluate the inbreeding level of the ex situ conserved Yangtze finless porpoise population living in Tian-e-Zhou National Natural Reserve, and to provide useful reference information for its population genetic management, 21 polymorphic microsatellite loci were utilized in this study to conduct parentage identification and to analyze relatedness among individuals in this population. As a result, three whole families with certain parents and offspring, together with 1 mother-offspring and 1 father-offspring pair have been detected. Yet, it is impossible to evaluate the inbreeding level of this ex situ conserved population according to so few parentages information. Nevertheless, relatedness analysis showed that the average relatedness index (r) of this population was 0.1182, and of the candidate parent pairs it was 0.1152. Both of them were significantly higher than those of the wild population living in the Poyang Lake. Additionally, in this ex situ conserved population, 26.14% of individual pairs have some relatedness (r > 0.2), which was 6 times higher than that of the wild population. Besides, inbreeding coefficient (Fis) of this population was 0.046. Results from both relatedness analysis and population inbreeding coefficient suggested that this ex situ conserved population is in high risk of inbreeding or has already been suffering from inbreeding. To prevent this ex situ conserved population from inbreeding or at least to mitigate the inbreeding level, on one hand, we recommend removing the adult female F34 and male M45 from this population because they had so many possible relatives. On the other hand, we recommend reintroducing two fertile porpoises (with an optimal sex ration of 1:1) every generation (about 5 years) from wild population or other ex situ conserved populations. Besides, to facilitate future population genetic management, constructing an accurate genetic studbook was proposed for this ex situ conserved population.