| The interaction between predator and prey has been an important theme and frontier in ecological research.Direct predation by predators leads to changes in prey behavior,population,community and food web characteristics.At the same time,acoustic,visual,tactile and olfactory cues that convey information about predation risk can also have non-consumptive effects and can induce stress responses in prey,thus having profound effects on prey populations,behavior and physiology.Previous studies have focused on the effects of direct predation on prey,while the patterns and processes of non-consumptive effects of predators on prey remain unclear,especially for bats,which are almost exclusively nocturnal.Bats are the only volitant mammals,and with high taxonomic and ecological diversity.The temporal ecological niche of bat activity does not largely overlap with diurnal raptors,and thus it was long thought that bats may experience less predation than other nocturnal small mammals,especially temperate bats.However,there is growing evidence that bats are also subject to high levels of predation pressure.For example,predation affects bat population dynamics and behavioral strategies such as habitat and commuting path selection,circadian rhythm variation,as well as mate choice.However,how predation pressure affects stress responses and changes in gene expression in bats remains unclear,and research is urgently needed.In this thesis,the Asian particolored bat(Vespertilio sinensis)was used as a research object,integrating behavioral(behavioral observation and acoustic playback),ecological(environmental factor monitoring and population size statistics),physiological(hormone measurement),and transcriptomic(gene expression analysis)theories and methods to investigate the effects of predation pressure created by the Amur falcon(Falco amurensis)on V.sinensis.We investigated the effects of predation pressure created by F.amurensis on the circadian activity rhythm,emergence behavior,food intake,stress hormone secretion,gene expression,and population size of V.sinensis.The results of the study are as follows:Predation pressure and mammalian state were classified and combined with environmental data.The effects of predation pressure on the circadian rhythms of V.sinensis were explored by linear mixed model construction and hierarchical partitioning analysis.The results showed that during the lactation period,bats exhibited earlier onset of emergence and later return to roosts.There were significant differences in the first emergence time,median emergence time and final return time of V.sinensis under different intensity of predation pressure,and the predation pressure mainly affected the median emergence time and final return time of V.sinensis.The hierarchical partitioning analysis revealed that light intensity had the highest independent contribution to the first emergence time,median emergence time and final return time of V.sinensis,suggesting that light intensity may be a top factor influencing the diurnal activity rhythms of V.sinensis.These results suggest that despite the risk of predation,the high energy demand of V.sinensis during lactation may be the main reason for their risk-taking behavior strategy.Previous research has shown that the distress cries made by bats when they are preyed on can attract conspecifics and may also cause bats to emergence their roost delayed.We played back two types of distress calls made by natural predators and human-controlled bats at the emergence pathways of bat roosts,and examined the differences between the two playback groups of V.sinensis in terms of vocal behavior and emergence time.The results showed no significant differences in the number of echolocation pulses of V.sinensis between the two distress call playback groups and control group,and no significant differences in the first emergence time,median emergence time and emergence duration of V.sinensis between the two playback groups and the control group.The presence of a real predator may have a stronger effect on bats than distress call playback,and the larger population of V.sinensis,which provides a higher risk dilution benefit for individuals within the population,may have resulted in distress call playback not having a significant effect on echolocation behavior and emergence behaviour of V.sinensis.Distress calls transmit the emotional state of the emitters and predation information to the conspecifics,and may induce a stress response similar to that of the emitters.We broadcast two types of distress calls for V.sinensis indoors and tried to elucidate the effects of predation stress on stress hormones and gene expression in V.sinensis.The results showed that there was no significant effect of distress call playback on the food intake of V.sinensis,although playback did not significantly affect the food intake of V.sinensis,the body weight of V.sinensis decreased with both distress call playback;this indicates that the stress response induced by playback had an effect on the appetite of V.sinensis,and at the same time,to cope with the stress,V.sinensis needed to exert more energy expenditure,which led to a decrease in body weight.The results of the linear mixed model analysis showed that the playback of the two distress calls did not have a significant effect on the concentration of glucocorticoids in V.sinensis,and the concentration of glucocorticoids in both groups of V.sinensis showed an increasing trend after playback;furthermore,the playback of distress calls had a significant effect on the concentration of triiodothyronine,which showed a decrease in the concentration of triiodothyronine in V.sinensis after playback.Both hormones are associated with memory consolidation,so changes in hormone concentrations in e V.sinensis may be designed to reduce fear memory consolidation.In addition,compared to the control group,transcriptome sequencing results showed that a total of 983 genes were significantly differentially expressed in the two distress call playback groups.GO(Gene Ontology)enrichment analysis and KEGG(Kyoto Encyclopedia of Genes and Genomes)analysis showed that differentially expressed genes were mainly enriched in pathways related to stress response,memory consolidation and immune-related pathways.Thus,these results suggest that chronic predation stress leads to stress responses in V.sinensis,while in order to reduce the effects of fear,V.sinensis exhibit reduced memory consolidation responses,thereby mitigating the negative effects of fear on health.By observing the emergence time and predation behavior of F.amurensis and their changes,combined with the estimation of the population size of V.sinensis,it can be determined whether predation by F.amurensis will affect the population size of V.sinensis.The results showed that light intensity and bat emergence time significantly affected the emergence time of F.amurensis,possibly reflecting the strong inhibitory effect of low light intensity on visual acuity of F.amurensis,such that F.amurensis would adjust their emergence time according to light intensity to obtain the maximum benefit.Mainly at dusk,F.amurensis predation on V.sinensis,and we observed two types of predation behaviors(aerial predation,waiting for search predation)and three feeding behaviors(perch feeding,aerial feeding,and temporary caching before feeding)during three consecutive years of predation behavior observations.Aerial feeding occurred in only two twilights,but caching behaviour emerged and was preserved in 2022,suggesting that caching behaviour is an innovative behavior.Further time series analysis showed that the average predation efficiency of F.amurensis using innovative feeding behavior was 3.10 times higher than that of other F.amurensis;moreover,the predation efficiency of F.amurensis increased by 2.2 times after the emergence of innovative behavior compared with that before the emergence of innovative behavior,confirming that innovative behavior can significantly improve the predation efficiency of F.amurensis.Through actual observation and prediction,the actual number of preyed V.sinensis were observed to be 22,138,193 and 279 in each evening from June to September of 2018 to 2021,respectively;and the predicted number of preyed V.sinensis were 33,292,366 and279 in each evening,respectively,which accounted for 0.50%,4.63%,5.81% and4.43%.This percentage is significantly higher than the results of previous studies(0.1%-1%),indicating that predation by F.amurensis can have a certain level of negative effects on the population of V.sinensis.In summary,predation pressure affects the circadian behavioral strategies of V.sinensis and also induces stress responses in V.sinensis,resulting in increased secretion of stress hormones and expression of genes related to stress or immunity in V.sinensis.These results suggest that predation pressure negatively affects body mass and thus reduces fitness in V.sinensis.In addition,this study also showed that raptors can also have some negative effects on the population size of temperate bats,but such negative effects have been underestimated.This study systematically investigated the effects of predation pressure on bats at multiple levels of gene expression,physiology,behavior,and population,which contributes to an in-depth understanding of the relationship between predator birds and prey bats,enriches the theory of fear ecology to a certain extent,and will provide a scientific basis for the conservation of raptor and bat diversity. |
