Study On The Response Of Echolocation Call And Body Temperature To Weather Change In Great Leaf-nosed Bats

Acoustic signals mediate a variety of life history events in animals,including resource competition,mate selection and species identification.It is therefore proposed that acoustic signals play a major role in the maintenance of stability of animal population and community.Acoustic signal is the carrier of acoustic information.Different acoustic information resides in different acoustic parameters and acoustic characteristics,which affect the fitness of animals.Climate change could drive the evolution of animal acoustic signals on a long time scale,and could lead to the adjustment of acoustic signals on a short time scale.The physiological change hypothesis believes that weather conditions could affect echolocation call frequencies of bats through changes in body temperature.The sensory drive hypothesis suggests that animals should adjust their vocalizations,such as lowering the call frequency to ensure sufficient range of signal transmission when atmospheric attenuation increase.It has been confirmed that changes in body temperature could cause changes in ectothermic animals' acoustic signals but how body temperature affect endothermic animals' acoustic signals is still unclear.In the background of global climate warming,how animals adjust their acoustic signals to cope with change in atmospheric attenuation and physiological conditions caused by climate change remains to be further studied.As the second largest group of mammals,bats occupy a unique niche in the night sky and are a model species for acoustic study.We conducted experiments with the Great Himalayan Leaf-nosed bat Hipposideros armiger.We integrated experiments in the field and laboratory to study whether bats change body temperature and echolocation call characteristics in response to climate change,and test the physiological change hypothesis and sensory drive hypothesis.1)We recorded the echolocation calls of the same population of bats in the field and measured the body temperature,exploring the effect of body temperature on echolocation call frequency between individuals.2)We transferred the bats to the recording room with low environment temperature and simultaneously recorded an hour's changes in body temperature and echolocation calls to explore the relationship between the peak frequency of echolocation call and body temperature.3)We recorded echolocation calls in the laboratory under semi-natural conditions and measured body temperature,the ambient temperature,humidity,and atmospheric pressure over three months from summer to early winter to investigate how weather affect the echolocation call.We found that: 1)In the same population,body temperature was positively correlated with the peak frequency between individuals.2)Bats emitted echolocation calls of lower frequencies with decreasing body temperature caused by decreased ambient temperature in lab,with an average call frequency shift of 170 Hz/°C,supporting the physiological change hypothesis.3)The ambient temperature,humidity and atmospheric attenuation in the recording room decreased significantly with days from summer to winter.The body temperature significantly decreased with ambient temperature.The peak frequency of bat increased significantly with days,from 70.78 ±0.45 k Hz to 71.52 ± 0.42 k Hz.The duration of echolocation call increased significantly with days,from 6.30 ± 0.64 ms to 6.69 ± 0.58 ms,and the bandwidth did not change significantly.The call frequency was negatively correlated with body temperature,which did not support the physiological change hypothesis.Instead,the call frequency was negatively correlated with ambient temperature,relative humidity and degree of atmospheric attenuation,supporting the sensory drive hypothesis although the magnitude of reduction in atmospheric attenuation caused by reduction in call frequency was smaller than the effect caused by the change in atmospheric conditions.The duration was not significantly dependent of atmospheric attenuation,but negatively correlated with the ambient temperature,and increased as the ambient temperature decreased.Bandwidth was not significantly dependent of atmospheric attenuation.In conclusion,in the same population,changes in body temperature could cause changes in echolocation call frequencies between individuals.Our results suggested that weather conditions can affect the echolocation signals of bats via the effects on their body temperature and on atmospheric attenuation.When both effects coexist,weather-induced adjustments in the echolocation signals could be more likely to be driven by the atmospheric attenuation effect.This paper proved for the first time that weather changes can affect the physiological conditions of bats and thus affect the echolocation call frequency,revealing the effects of atmospheric attenuation and physiological effects on the echolocation call.