Individual Differences And Trade-offs Of Energy Strategies In Response To Photoperiodic Changes And Food Restriction In Siberian Hamsters (Phodopus Sungorus)

To deal with the challenges of the low temperatures and food shortage in winter,animals have evolved different energy strategies such as migration,molting,hoarding,fat storage and torpor,but there may be individual differences and trade-offs among strategies.Some researchers suggested that there may be trade-offs between energetic strategies such as hoarding and torpor,etc.,in Phodopus sungorus.Here we explored whether there are trade-offs between various energy strategies such as hoarding and torpor,to analyse the causes of individual differences in energy strategies responding to warm temperature and long light,low temperature and short light and ad-libitum-feeding stage or food restriction,as well as the differences of gut microbes among individuals with different phenotypes.In this study we tested the effects of temperature,photoperiod,sex and ad-libitum-feeding or food fasting on body mass,changes of body mass,food hoarding,food intake,total intake,core body temperature and activity.The results showed that:1)The changes of temperature and photoperiod had no effect on the body mass of Phodopus sungorus.The body mass of the male is larger than the female,but there is no difference in food intake between the two sexes;the basal metabolic rate,core body temperature and activity of females were higher than those of males.In the low temperature and short light environment,the food intake of all individuals increased,but the hoarding size did not change.That is the one of the reasons for individual weight increased in low temperature and short light environment.2)In the ad-libitum-feeding stage,None of the animals had spontaneous daily torpor;In the 70% stage of food restriction,only a few individuals appear torpor.When entered the 50% stage,a large number of individuals began to express torpor.The core body temperature of all individuals increased gradually with the increase of food restriction,and decreased significantly at 50% stage.And with the increase of food restriction,the increase of individual activity is caused by the individual's desire for food.The phenomenon of individual death after food restriction shows that when food restriction induces torpor,if the animal cannot start torpor in time to save energy,it may die.3)The food intake and weight gain of the non-torpor group in the warm temperature and long light and ad-libitum-feeding stage are higher than those of the torpor group,indicating that the non-torpor group may tend to store internal fat under the appropriate environment,and use fat as internal energy to adapt to adverse environmental changes under low temperature and short light environment.On the contrary,in response to adverse environment,the torpor group will reduce body temperature and save energy by expressing torpor.Meanwhile,the expression of torpor may conducive to storing energy for reproduction,and the birth interval of torpor individuals is shorter.4)Individuals choose different survival strategies in low temperature and short light environment.There were four kinds of individuals in the population,which are hoarding and torpor(about 24%),hoarding but do not torpor(about 13%),not hoarding but torpor(about 39%),and not hoarding and do not torpor(about 24%).They were not more inclined to one of the two strategies of hoarding and torpor,at least there is no trade-off between food hoarding behavior and fasting-induced torpor.Those who choose food storage are not more inclined to torpor,and there is no significant difference in food storage in the torpor group.5)There were significant differences in gut microbes between torpor and non-torpor only under the condition of warm temperature and long light without food restriction,which may be related to their food intake differences.There were significant differences in gut microbes between all individuals in warm temperature and long light without food restriction and those in low temperature and short light with food restriction(sach as,proteobacteria,bacteroidota and verrucomicrobia),indicating that these differences were mainly affected by temperature,photoperiod and food restriction.