Research On The Development, Diversity And Ecological Plasticity Of Vocalization In Myotis Macrodactylus

The big-footed myotis, Myotis macrodactylus, belongs to the genus Myotis(Microchiroptera, Vespertilionidae). It is naturally rare with unknown population trends and ithas been listed as a Least Concern species by the IUCN. In2008, M. macrodactylus, mainlyinhabiting in dark cave with a colony of over1000in the natural condition, was first found inChina. In this paper, aimed at exploring the hotspots and difficulties in the acoustic researcharea of bats, M. macrodactylus was chosen as the research object considering itsrepresentative inhabitation pattern and call types, and three main aspects, including postnataldevelopment of vocalization and wings, diversity of social calls and plasticity of echolocationcalls emitted by adult bats, were carried out through the combination of field work and indoorexperiment. The specific researchs are as follows:1. Young big-footed myotis bats were born in early July in Dalazi cave, located in Ji’an,Jilin Province and infant vocal calls and wing shape datas were collected using themark-recapture methodology. Our results suggested that neonates emitted long echolocationcalls with multiple harmonics with most energy distributed on the first harmonic. The infantscan emit isolation calls which are used to recognization between infants and maternal bats.The infants emitted calls with frequency modulation and short duration at age of7days,which developed into the echolocation calls in later phase. At the age of22days when theinfants could fly clumsily. At the age of40days when it was difficult to distinguish between ainfant and an adult, the echolocation calls had two harmonics with the peak frequency rose upto a frequency near that of the echolocation calls emitted by the adult. The energy of thepulses distributed mainly on the first harmonic and had a decreased duration, which had nodifference with pulses from adults. Our study on the development of vocal calls during flightin the big footed bat infants showed that the early forms of echolocation calls may be aninnate call type. The result shed light upon the solution to the call type discrimination of theinfants and helped to reveal the origin the echolocation pulses and the neurophysiologicalmechanisms of vocalization in bats. In addition, we also studied the postnatal development of infant vocal calls and flight andthe results suggested that the infants had a mean wingspan of12-15cm and a wing area of30-40cm2at the age of4days and had a higher growth rate before the age of22days,however after that the growth rate decreased to a steady state and could fly clumsily in thecave. Our results also suggested that the wingspan and the wing area of the young reached91.9%and86.1%of the adult respectively at the age of40days and no significant differencewith wing shape of adults was found, which indicated that the postnatal development periodof wing is about40days. Of the three nonlinear growth models (Logistic, Gompertz, and vonBertalanffy), the logistic equation provided the best fit to the empirical curves for wing spanand wing area. Our results defined that the wingspan and wing area can be evaluated usingpostnatal days, and flight capability can be predicted simultaneously.2. Vocalizations and behaviors of five pregnant big-footed myotis bats were recordedsimultaneously, and the social calls emitted by the last individual approaching the clusterwere also recorded. Through the analysis of the diversity and structure of social calls, thatbig-footed myotis can emit four syllable types making up10simple monosyllabic calls and27complex multisyllabic calls was found. The sequences of pulses in big-footed myotis callshave a stable pattern. All of calls began with a downward frequency-modulated component,and can form complex multisyllabic calls through combining with one or two other threesyllables. On this rule, calls diversity were varied with the increased or decreased number ofsyllables and syllable types and differences among maximum frequencies and durations ofindividual calls demonstrated significant. In addition, the time spent on returning the colonyby each bat was negatively correlated to their call diversity. The results indicated that femalebig-footed myotis bats can produce different social calls to transfer information in order to anexact recognization. We suggested that individuals emitted diverse social calls under naturalselection in order to be more easily identified by others.3. Under natural circumstances, echolocation pulses from big-footed myotis bats wererecorded as these animals searched for prey in five habitats differing in relative clutter level.Results showed that overall frequency, pulse duration, and frequency modulation rates (MRs)occurring within each pulse all varied across habitat and MRs associated with each of the three elements making up each pulse was positively correlated to relative clutter level in eachenvironment. These results suggested that the echolocation call is plastic and big-footedmyotis can dynamically modify multiple dimensions of pulse structure in adapting to theperceptual challenges of particular foraging habitats.In conclusion, this study briefly replayed the evolutionary process of bat vocal callsthrough analyzing the development process of vocal calls based on the history of bats. In thefurther studies, playback experiments under multiple backgrounds will be necessary todetermine the relationship between behaviors and acoustic signals in bats, which cansystematically reveal the traits and functions of the social calls of big-footed myotis. Inaddition, further studies will be necessary to determine the relationship between changes inmodulation rates and the specific goal in these vocalizations, which can help to reveal themechanism of the auditory nerve processing and the behavioral adaptation.