| Global biodiversity is under threat from climate warming,and the physiological tolerance of species will directly face the challenge brought by global warming.Except for the A.sinensis(Chinese alligator),A.mississippiensis and C.acutus in the middle latitudes,the rest of the crocodilians are distributed in the tropical region,and the unique latitude distribution pattern reflects the high dependence of the crocodilians on temperature.Under the background of global warming,this study took the Chinese alligator(distributed in the northernmost limit in crocodilians species)as the main research object,and Crocodylus siamensis distributed in tropical areas as the control group.According to the latitude distribution characteristics of the two crocodiles species,temperature domestication experiments were carried out to study the basic metabolism and growth characteristics of the two crocodiles species under the background of high and low temperature domestication.Based on the metabolome data and proteome data of the high,low and extremely low temperature stress groups of the two crocodiles,the molecular regulatory mechanism of temperature response of the two crocodiles was discussed.And the 16S r DNA sequencing method was further used to study the response process of host microorganisms of the two crocodiles under high and low temperature domestication,aiming to reveal the temperature adaptation characteristics of Chinese alligators adapted to the northernmost limit distribution at the physiological and host microbial levels from the differences in response to temperature changes between the two crocodiles.On this basis,combined with the species distribution model and the system conservation planning tool,the ecological response process of Chinese alligator to global warming was analyzed from the habitat level,and the following results were obtained:(1)The results of body temperature and heart rate monitoring showed that the mean body temperature and mean heart rate of A.sinensis before domestication were 29.48±0.56℃and 56.80±2.06 times/min,respectively.The mean body temperature and mean heart rate of C.siamensis before domestication was 29.6±0.52℃and 53.16±3.16 times/min,respectively.There was no significant difference between the two groups.The change of ambient temperature significantly changed the body temperature and heart rate of the two crocodiles species(After high temperature acclimation,the mean body temperature and mean heart rate of A.sinensis were 32.05±0.22℃and 64.69±2.40 times/min,respectively,and that of C.siamensis were 31.82±0.47℃and 67.72±3.25 times/min,respectively.After low temperature acclimation,the average body temperature and heart rate of A.sinensis were 23.42±0.57℃and 50.53±2.90 times/min,respectively;the average body temperature and heart rate of C.siamensis were 22.7±0.47℃and 46.29±4.65 times/min,respectively).The two alligators cope with the high temperature environment by increasing their basal metabolic rate,and cope with low temperatures by lowering your basal metabolic rate.At the same time,the environmental temperature significantly affected the food intake,growth rate and condition factor of the two crocodiles species,and the food intake,growth rate and condition factor of the two crocodiles species were higher under high temperature domestication than under low temperature.In addition,the fatness and body weight of Chinese alligators still showed an increasing trend under low temperature domestication,while that of C.siamensis showed a decreasing trend,indicating that Chinese alligators showed stronger adaptability under low temperature domestication than C.siamensis.(2)The metabolomic and proteomic data showed that compared with the high-temperature acclimation group,both C.siamensis and Chinese crocodiles had metabolic compensation effects under low temperature acclimation:the expression of intermediate metabolites and enzymes increased in the TCA cycle(e.g.,pyruvate,isocitrate,α-ketoglutarate,malate dehydrogenase 1,and malate dehydrogenase 2)and glycolytic pathways(e.g.,6-phosphate glucose,D-ribulose,beta-D-glucosamine,phosphopyruvate hydratase,fructose-diphosphate aldolase,L-lactate dehydrogenase,glyceraldehyde-3-phosphate dehydrogenase,pyruvate kinase,glucose-Increased expression of intermediate metabolites and enzymes of 6-phosphate isomerase,phosphoglycerate kinase and phosphoglycerate tautomerase).As the temperature continued to decrease(34℃,25℃to 16℃),compared with the low temperature group,the metabolic compensation effect in the TCA cycle and glycolysis pathway in the extremely low temperature stress group turned to an inhibited state in C.siamensis,and the metabolic compensation effect was still present in the enzyme level of the TCA cycle,the metabolite level in the glycolysis pathway and the enzyme level in the Chinese alligator.At the same time,Chinese alligators also showed significant compensatory effects in hypoxic adaptation,material circulation,and neural regulation,suggesting that Chinese alligators can respond to low temperature environments through metabolic compensation and enhanced neuroregulation(sustained up-regulation of neuroactive ligand-receptor interactions).And with the decrease of temperature,C.siamensis may be accompanied by increased oxidative damage in the body.(3)The 16S rDNA analysis results showed that the Alpha diversity of cloacal microbiome underwent more drastic changes than that of oral microbiome during domestication of the two species of crocodiles.The oral and cloacal microbial diversity of low temperature acclimated Chinese alligators and high temperature acclimated C.siamensis decreased in the early stage and increased in the later stage,and the relative abundance of Gottschalkia continued to increase.Under high temperature acclimation,the Alpha diversity of oral and cloacal microorganisms for the Chinese alligators continued to decline,accompanied by an increase in the relative abundance of conditioned pathogenic bacteria(Acinetobacter,Moracella,Corynebacterium,etc.),a decrease in the relative abundance of firmicutes and an increase in the relative abundance of Proteobacteria.(4)The suitable habitat for Chinese alligators continues to decrease under global warming,and the proportion of the decrease is related to climate scenarios.The suitable habitat area of Chinese alligators under SSP585(with the highest temperature rising)is reduced by 17.93%to 40.69%more than that under SSP126(with the lowest temperature rising).Climate change does not affect the elevation distribution of Chinese alligators,but it affects the centroid migration(westward migration)of Chinese alligators habitat.Overlaying Marxan’s optimal solutions across five scenarios(current and future),a total of 4 units were identified as priority protected areas covering 4km~2.In addition,compared with rainfall variables,temperature variables are more important in limiting the distribution of Chinese alligators(the total importance of the temperature variable in modeling was 62.2%).The results of this study reveal the characteristics of Chinese alligator adapted to the northernmost limit distribution in many aspects.Combined with the impact of global warming on the habitat of the Chinese alligators,this paper comprehensively reveals the physiological and ecological response processes of the Chinese alligators to temperature change,aiming to provide data support for the protection of Chinese alligators under global warming. |
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