利用下颌骨形态鉴别野生和饲养北美水貂的研究

当前,我国法律明令禁止对濒危野生动物进行猎杀、滥食以及非法交易,但鼓励人工饲养种群的规模化养殖和商业化利用。这引起一个重要问题:即从野外非法猎取的野生动物,会假借人工驯养繁殖的名义合法地进入市场,这对执法部门如何精准鉴定动物来源造成了极大的困扰。现有的依靠骨密度和头骨形态的鉴定方法不能满足需求。本研究以野外水貂(n=25)和人工驯养水貂(n=38)的下颌骨为对象,建立一个更为简便而有效的鉴别方法。下颌骨与咬肌构成一个杠杆系统,髁状突为支点,前臼齿和臼齿的齿尖为阻力点,各个齿尖到髁状突的距离为阻力臂。我们推测,野生水貂的食物质地较为坚硬,而人工饲养的动物食物柔软,因而野生水貂捕食和进食时需要更大的咬合力和咬合效率。这一差异在个体发育过程中很可能导致阻力臂结构发生变化。如果这种变化足够明显,就可以据此建立动物来源的判别指标。通过测定髁状突到前臼齿第3齿尖以及臼齿上的下原尖和下前尖的阻力臂、齿冠长及齿尖高等数据,建立了13个判别指标,利用这些指标分析野生与饲养个体间的差异并进行判别分析,以已知来源个体的正确回判率来评价其有效性。结果显示,与野生组相比,人工饲养水貂下颌咬合杠杆的阻力臂更长,支持了我们的推测。在13个判别指标中,H₂/L₂(臼齿下前尖高和其力臂长之比)和CosA(犬齿沿矢状面的倾角)无性别差异,二者联合使用时,已知来源个体的正确回判率可达到91.20%,具有很强的鉴别能力。由于水貂是典型的小型食肉动物,因此本研究的结果对其他小型食肉动物的鉴别也具有重要的参考意义。

Use of Mandible Morphology to Discriminate Wild and Farmed American Minks

The laws and regulations of China on wildlife protection prohibit hunting,illegal trade,and improper consumption of wildlife as food,but encourage large scale farming and commercial use of captive breeding populations.This raises the problem that illegally hunted wild animals can enter legal markets having been fraudulently labelled as farmed animals.This presents challenges for law enforcement to accurately identify the origin of animals in the wildlife trade.Existing identification methods based on bone density and skull morphology cannot meet the requirement.In this study,we used American mink as model for small carnivores to investigate the morphometric difference of mandibles between wild and farmed mink to establish indices for discrimination of origin.The mandibles of 25 feral and 38 farmed mink were collected and measured morphometrically.The mandible and masseter form a lever system,with the condyle as fulcrum,the cusps of premolars and molars as resistance points,and the distance separating cusp and condyle as a resisting arm.We hypothesized that the difference of load on the levers due to food texture and behavior between wild and farmed mink could give rise to ontogenetic and morphometric differences of levers.Based on the degree of differences discriminant indices could be established to differentiate wild from farmed mink.A total of 12 parameters(including resisting arm length between condyle to third cusp of premolar,the protoconid of molar,and the paraconid of molar)were measured and 13 indices were defined.Indices were used to analyze differences between wild and farmed mink,and were submitted to discriminant analysis.Correct assignment rates of mink of known origin were used to evaluate the effectiveness of the indices.Statistical comparisons showed that the resistance arms of the biting levers were greater in farmed than in wild mink,supporting our hypothesis and suggesting reduced ability to break down hard food items.Particularly,the ratio of paraconid height to its resistance arm and the cosine of the angle between the canine and the line from canine base to the condyle were both monomorphic.Combination of the two indices yielded correct assignment of up to 91%of mink to their correct source of origin.The American mink is a typical mustelid carnivore.Whether the two discriminative indices developed in this study might also be applicable to other small carnivores requires empirical testing.