Use Of Mandible Morphology To Discriminate Wild And Farmed American Minks

Most endangered species have economic values pursued by people through either hunting of wild individuals or setting up farms. Theoretically, farming would play important roles of conservation by providing sustainable products to the market and reducing exploitation demands of wild population. However, farming would become a stimulator of poaching if illegally acquired commodities from wild populations enter legal market in the name of farm origins. Thus discriminating the origin of wildlife commodities are essential for supervision of wildlife farming and ensuring the security of wild populations. Some methods have been proposed such as femur bone density and skull morphometrics based discriminations etc. The present study develops a novel method based on morphometrics of mandible and molar teeth using American mink as model (38 farmed animals and 25 wild animals).The mandible is regarded as a lever system of which the pivot is the condylar process, the resistant point is teeth cusps and the force arms are the mandible. We hypothesized that different texture and hardness of food of carnivores between farm (often soft) and wild (often hard) may influence the development and the lever system. It could be possible to set up indices for origin discrimination based on the difference of the lever system if it is significant enough. In order to test the hypothesis, we measured length of force arms between the condyle process and the third cusp of premolar and the protoconid and paraconid of molar, length of corona, height of cusp, and set up 14 indices namely L1/L, L2/L, L3/L, L1/M1, L2/M1, L3/M2, H1/L1, H2/L2, H3/L3, H1-L1/L2, H2-L2/L2, H3-L3/L2, H4·L4/L2 and CosA. Differences of these indices between sexes, wild and farm groups and effectiveness for origin discrimination were tested. Results showed:1. The structure of biting lever system could be altered by farming based on the comparisons between the two groups. Farm minks have longer resistance force arms implying weakened cutting efficiency.2. Among the 14 indices, the combination of H2/L2 and CosA would achieve 91.2% correctness of classification of known samples (CC).3. When sex is known, L2/M1 had the highest CC (78.8%) for males, and L1/M1 had the highest CC (87.9%) for females.4. Some indices with significant sexual dimorphism could also be used to test the sex. The combination of L1/L and L2/M1, and the combination of L1/M1 and L2/M1 could achieve CC of 87.3% and 85.7%, respectively.These results above suggest that mandible morphometrics (biting lever) could be used to discriminate the origin of mink with strong implications for the potential of origin test in other carnivores.