Research On Vocal Development And Vocal Learning Of Pups In Hipposideros Larvatus

Acoustic signal is an important communication carrier of animals.After birth,vocal animals will experience the development of acoustic signal and then form a series of vocalizations for community communication.At the same time,through the studies of vocal development and vocal learning of different animal groups,we can systematically reveal the biological basis of animal language and provide strong evidence to support the origin and evolution of human language.Earlier studies mainly focused on birds.However,compared with birds,the Chiropterans(commonly known as “bats”)of the class mammalia are more closely related to humans,and some bats display the behaviors such as vocal learning and vocal turn-taking that are directly pertinent for human spoken language.Therefore,the study of bats vocal development and vocal learning can expand the behavioral evidence of mammalian language research and provide some scientific basis for the exploration of the origin and evolution of human language.In this study,Horsfield's leaf-nosed bat(Hipposideros larvatus),belonging to the Chiroptera,family Hipposideridae and genus Hipposideros were selected as research subjects.In the breeding population of H.larvatus,vocal development and vocal learning ability of young bats were studied by combining field acoustic data collection and indoor playback experiments.The results were as follows:In natural populations,pups can emit a variety of types of isolation calls,including downward frequency modulation(DFM),arched frequency modulation(AFM),upward frequency modulation(UFM),and others.The acoustic parameters of DFM,AFM,UFM gradually change with the development.The frequency-related parameters(peak frequency,frequency of the first quartile,center frequency,frequency of the third quartile,minimum frequency,maximum frequency and bandwidth)significantly increase with the development(linear mixed-model analysis,LMMs,all P < 0.001).The Euclidean distance between three types of isolation calls and the corresponding social calls of adult bats decreased gradually during ontogeny,and the isolation calls tended to be the corresponding types in adult social calls.As pups developed,the monosyllables of isolation calls gradually changed into the composites that similar to the social communication calls of adult bats.Among them,the interval time between different types of monosyllables were significantly reduced(kruskal-wallis test,P = 0.000,df = 9),while the interval time of monosyllables between 1-day-old and 28-day-old was significantly different(Mann-Whitney U test,P = 0.000 < 0.05).The success rate of discriminant factor analysis(DFA)of different types of composites was 58.3%,which was significantly higher than the random discriminant rate(12.5%,binomial test: P < 0.001).The UFM syllables of isolation calls were slightly different in 1-day-old pups.For UFM syllables,principal component analysis(PCA)extracts two principal components with an eigenvalue greater than one.The DFA classified 71.2% of UFM syllables to the correct individual,which was significantly higher than expected by chance(10%;binomial test: P < 0.001).The higher discriminant score indicated that UFM syllable of isolation calls carried distinct individual tags.The first early echolocation calls were recorded 4 days post-partum.As pups develop,The interval and duration of echolocation calls decreases,while the peak frequency and bandwidth of frequency modulation increases.Significant differences existed in the echolocation calls of 40-day-old pups and adults(permutational analysis of variance,PMANOVA,DF = 1,F = 15.729,P < 0.01).No significant differences were apparent in interval and duration(independent sample t-test,all P > 0.0125,Bonferroni correction),but significant differences were found in the peak frequency and bandwidth of frequency modulation(Mann-Whitney U test,all P < 0.0125,Bonferroni correction).In the playback experiment of pups in the late development stage,the echolocation calls of the young bats in the low-frequency playback group presented a downward trend in the peak frequency after playback experiment,while the high-frequency playback group,the normal playback group and the non-playback group also showed a slight decrease in the peak frequency during fluctuations.There were significant differences between the four groups before playback and 30-days of playback(Mann-Whitney U test,all P < 0.05).For oscillatory frequency modulation(OFM)syllables of social calls playback experiment,both low-frequency and high-frequency playback can change the emission ratio of low-frequency and high-frequency calls of pups in OFM type syllables.Pups in the low-frequency playback group tend to emit more low frequency OFM syllables,while in the high-frequency playback group tend to emit more high-frequency OFM syllables.In the normal playback group and the non-playback group,there was almost no change in the proportion of low-frequency and high-frequency OFM syllables.In the final stage of playback experiment,there was a significant difference in the proportion of low-frequency and high-frequency OFM type syllables between the low-frequency playback group,high-frequency playback group and the non-playback group,the natural group(chi-square test,all P < 0.05),while there was no significant difference between the normal playback group and the non-playback group,the natural group(chi-square test,all P > 0.05).To sum up,this study found that the isolation calls of H.larvatus pups are diverse,which changed with the development of acoustic parameters and tended to be the type of adults.It is the first time to find the syllable merge during the development.It is speculated that UFM syllables can encode the individual information of pups to facilitate the identification of female bats.The echolocation calls of pups have different origins and developmental trajectories from the isolation calls.The playback experiments suggest that pups have vocal learning ability.The results added behavioral evidence to the studies on Chiropterans,enriching the study of vocal development and vocal learning in mammals.It is further confirmed that Chiropterans can be used as a model group for the study of mammalian language.It provides important reference for the following similar research.