| Chinese alligator(Alligator sinensis)is one of endangered and rare reptile for China.According to historical records,Chinese alligators have been widely distributed in the middle and lower areas of the Yangtze River.Due to environmental damage,habitat loss and human-killing,the number of this species is rapidly declining and on the verge of extinction.However,rejuvenation work of the population is remarkable after nearly 40 years of protection,and has increased significantly.Therefore,the study on strengthening the reproductive,ecological and behavioral mechanisms of Chinese alligator is necessary for the scientific management and sustainable development.In order to meet the complex environmental changes and improve the genetic quality,animals usually respond in behavior such as nest-selection and mate choice strategy.However,it is still unknow about the relationship between the environmental factors,temperature and reproductive characteristics as well as the molecular mechanism of mate choice for Chinese alligator.Based on this,the research is carried out in the Changxing alligator nature reserve.the main works included: 1)observe the behavioral spectrum;2)investigate and calculate the environmental factors,temperature and reproductive index of the nests;3)paternity analysis for offsprings to analyze the multiple mating,and 4)analyze the molecular mechanism of mate choice from the perspective of MHC Class I and SSR gene.The main findings are as follows:(1)The behaviors of the Chinese alligators were observed,mainly including thermoregulatory behavior,reproductive behavior,communication behavior,motor behavior,feeding behavior,conflict behavior,homosexual behavior,and other behaviors.(2)Comparisons of environmental factors between the core region and reintroduction region were conducted,results showed that the nearest tree distance and the mean water distance in the core region were 0.99 m and 2.47 m,while that were 0.69 m and 4.59 m in the reintroduction region.Canopy openness of 82% nests was above 0.8,while only 32% was above 0.8.Hatching success rate between the two regions showed no significant difference(P = 0.817)but body weight and body length of offsprings were significant difference(body weight: P < 0.001;body length: P = 0.005).In addition,snout tail length of female in the core region was positively correlated with clutch eggs,body weight of offsprings(P < 0.05),for the reintroduction region,positive correlation between snout tail length of female and body length of offsprings(P < 0.05).The nest temperature fluctuation was significantly negatively correlated with the hatching success rate(P < 0.01).The canopy openness and the nearest tree distance was correlated with the mean temperature in the nest analyzed by the multiple linear regression analysis.(3)We conducted maximum-likelihood-based parentage analysis for offsprings in 2015~2017.In this study,13 microsatellite loci were used to perform paternity tests for 31 clutches of mother-known in the core region.Fathers of 12 clutches were successfully identified.Meanwhile,parentage analysis was also conducted for 35 clutches offsprings which mother and father were unknown in the reintroduction region,and mother of 28 clutches and father of 30 clutches were successfully identified.In all,there are 69 families in the core and reintroduction region,94.2% clutches had a single father and only 5.8% clutches had two fathers.The multiple paternity phenomenon occurred only in the core area,and the reintroduction region exhibited a single father.(4)We found that breeding males had a higher Ho frequency at MHC I1327e3 locus than randomly sampled males(P = 0.001),which supported the heterozygous advantage hypothesis.Meanwhile,MHC-heterozygous males harbor a greater reproductive success,which possibly was the reason that those males were more preferred by the females than MHC-homozygous males.Furthermore,for MHC I1327e3 locus,amino-acid distance and functional distance of true mating pairs were higher compared with that of randomly sampled pairs(amino-acid distance: P = 0.031;amino-acid functional distance: P = 0.031),which supported the compatible gene hypothesis.Analysis of pairwise relatedness revealed that despite mate choice,individuals did not completely avoid inbreeding.Conclusion: Firstly,this study establishes the behavioral spectrum of Chinese alligator and reports suspected homosexual behavior.Secondly,the canopy openness,the nearest tree distance and the mean nest temperature have significant effects on the hatching success rate.Thirdly,parentage analysis shows that about 95% clutches harbor a single father.Finally,mate choice of female supports the heterozygous advantage hypothesis and compatible gene hypothesis,and does not avoid inbreeding.The results of this study will be of great significance for the further improvement and management of artificially repopulated populations. |
