Discrimination Mechanisms In The Chinese Crocodile Lizard (shinisaurus Crocodilurus)

Chinese Crocodile Lizard (Shinisaurus crocodilurus Ahl) which should receive specially protects is preserved as the first class protected animal in China and included the CITES Appendix in II in 1989. Until now, individual discrimination was mainly reported in mammalian and there was no report on discrimination mechanisms in reptile in China. In order to reveal the discrimination mechanisms of Chinese crocodile lizard, we studied its prey and individuals discrimination mechanisms. Studies on the discrimination mechanisms of Chinese crocodile lizard are helpful to gain insight into its foraging behavior and chemical communication. The main results are as follows:1.Prey discrimination mechanisms: we studied its prey discrimination mechanisms through two series experiments. In the first experiment, we wetted the swab by deionised water, cologne, smashed earthworm and smashed tenebrio as the chemical cues and observed the response of 11 Chinese crocodile lizard. Each individual was tested 24 experiments to each stimuli. The results showed that all individuals of Chinese crocodile lizard responded to the swabs by tongue flicking and the number of tongue-flicks in response to tenebrio and earthworm stimuli was significantly higher than that to cologne and deionized water. It meant that the Chinese crocodile lizard could discriminate food and non-food stimuli. In the second experiment, we observed the responses of Chinese crocodile lizard to the following cues: (A) blank utensil, (B) the utensil was wetted by smashed earthworm, (C) the alive earthworm was sealed in the utensil, (D) alive earthworm was kept in the open utensil. Each individual was tested 5 experiments. Results showed that the Chinese crocodile lizard for each cues was significantly different in dealing time, investigation frequency and attack frequency. The dealing time was significantly different both between A and B, but aslo C and D. The investigation frequency was significantly different between A and B. The investigation frequency and attack frequency were not different significantly between C and D. It implied that the Chinese crocodile lizard rely more on visual senses to discriminate prey than on chemical cues. The prey discrimination mechanisms of Chinese crocodile lizard may be correlated with foraging mode, phylogeny and prey.2.Individual discrimination: In order to understand the ability of crocodile lizard (Shinisaurus crocodilurus) discriminating familiar and unfamiliar individual, we studied its chemical discrimination mechanisms. The results showed that the number of tongue flicking and latency time among familiar, unfamiliar and control odours were significant different. The number of tongue-flicks in response to female unfamiliar odours for male was significantly higher than that for familiar, but the latency time was not significantly different between familiar and unfamiliar odours. The number of tongue-flicks and latency time in response to familiar and unfamilar male odours for female were not significant different. The results showed that the crocodile lizard could discriminate familiar and unfamiliar individuals through chemical cues. This kind of discrimination is important for the mating of crocodile lizard. The results of visual and chemical experiments showed that the number of tongue flicking and maximum aggression and atack frequency among familiar, unfamiliar and control odours were significant different, but the latency time in response to unfamiliar odours for male was significantly shorter than that for familiar. However, the number of tongue-flicks was not significantly different between familiar and unfamiliar odours after three days, it showed that chemical cues did not play a key role in individual communication. Additionally, the maximum aggression and attack frequency or Approach frequency were not significantly different between familiar and unfamiliar individuals, this showed that the crocodile lizard (Shinisaurus crocodilurus) discriminated familiar and unfamiliar individual base on behavior trait as shaking head and push-up. We speculate that males use their visual ability to find females but then rely on chemical cues to assess the receptivity of females once the pair are in close proximity. Visual signals are important at distance while chemical signals are important during close encounters in individual discrimination.3. Kin discrimination mechanisms: kin experiment showed that the number of tongue flicking and latency time among kin, non-kin and control odours were significant different. The number of tongue-flicks in response to kin for juvenile and female respectively was significantly higher than that for non-kin,. It implied that juvenile can discriminated sibling and non-sibling,and female can discriminated kin and non-kin juvenile.While juvenile can not discriminated kin and non-kin female because the number of tongue-flicks and latency time between kin and non-kin female were not significant different .The results in experiment of odours discrimination between unfamiliar kin and familiar kin juvenile showed that the number of tongue flicking in response to non-kin juvenile odours for female was higher than that for kin juvenile, it showed that familiarity could be established through long time contact and the coexist individual may be treated as kin individual. These results suggest that familiarity may be a mechanism of kin discrimination in the crocodile lizard. Different discrimination mechanism may be taken at different stages of growth process in the crocodile lizard. The kin discrimination mechanism was familiarity or phenotype matching, or both. It need combine molecular biology and neurobiology to further study the relation between kin recognition mechanism, kinship structure and avoid inbreeding and nepotistic, and the interaction with ecological factors. Kin discrimination is helpful to understand the evolution of behavior and regulation mechanism.