Geographical Evolutionary Divergence In Acoustic Signals Of The Great Himalayan Leaf-nosed Bat

Uncovering the causes and forces of population divergence in phenotypic traits is afundamental goal in evolutionary biology and ecology. Acoustic signals are basic means forindividual communication and environmental perception in animals. Animals’ acousticsignals often vary geographically and are considered as good models to explore evolutionaryand ecological processes, such as population divergence, niche differentiation and speciation.Bats are the second largest order of mammals and occupy a nocturnal aerial niche.Echolocating bats not only have rich vocal repertoires for communication, such as forindividual recognition, mate attraction, predator avoidance, and territorial defense, but alsoproduce echolocation signals for navigation, orientation, and prey detection. However, littleattention has been paid to geographical variation in bat communication vocalizations.Especially, rather little is known about the differences or similarities between geographicalvariation in echolocation and communication vocalizations. To what extent arecommunication vocalizations divergent between populations of bats? What evolutionarycauses and forces have driven population divergence in these two kinds of vocalizations?Echolocation and communication vocalizations are acoustically, behaviourally, andfunctionally distinct, so will the patterns, causes and forces of geographical variation bedifferent between them?Here, I studied the geographical variation in echolocation and communicationvocalizations of a widespread bat species Hipposideros armiger in South China, and assessedwhether the acoustic divergence was related to variation in genetic (population history,population genetic structure, and genetic distance), morphological (forearm length),environmental (mean annual temperature, mean annual relative humidity, mean annualprecipitable water, and sound transmission rate) or geographical (geographical distance,latitude, longitude, and elevation) factors and was driven by either ecological selection, orcultural or genetic drift.To provide a clear genetic background for the study on acoustic geographical variationin H. armiger, I first assessed the population history and genetic structure of this species,using two mitochondrial DNA (mtDNA) markers (cytochrome b and control region) andseven nuclear microsatellite loci (nSSRs) from216individuals sampled across the species’known distribution region. The H. armiger has high genetic diversity and comprises sevengenetic clades, i.e., Eastern China-Taiwan-Hainan, Western China, SouthwesternChina-Northern Vietnam, Southwestern Yunnan, Truong Son Mountains, Southwestern Thailand, and the South Himalayas. The time to most recent common ancestor of allexamined H. armiger individuals could be traced back to1.35million years ago (Ma). Thisspecies experienced multiple lineage divergence and demographic expansion events, and thebasic phylogeographical structure of H. armiger was established by0.24Ma. There wassignificant population differentiation and genetic structure in H. armiger. Nonetheless,substantial gene flow has been detected between populations from different geographicalregions.I recorded echolocation pulses emitted in the resting state of H. armiger from17localities in Eastern China, Western China, Hainan, and South Yunnan. The peak frequencyof echolocation pulses varied significantly across populations sampled, with the maximumvariation of about6kHz (66.80-72.51kHz). Most acoustic variation was attributable todifferences between regions. The peak frequency clustered into three groups: Eastern andWestern China, Hainan, and Southern Yunnan. The population differences in echolocationpulses were significantly related to morphological variation which was correlated with meanannual temperature. Moreover, the acoustic differences were significantly correlated withgeographical distance after controlling for “morphological distance”. These results suggestedthat the action of both indirect ecological selection and cultural drift promote, in part,divergence in echolocation vocalizations of individuals within geographically distributedpopulations.I also recorded communication vocalizations of H. armiger under natural conditions in9of the17localities. This species exhibited rich vocal repertoires with36syllable typesstatistically classified. We selected13the most frequent syllable types for geographicalvariation analysis and the results showed that all of them exhibited significant differencesamong populations. Most acoustic variation in communication syllables was attributable todifferences within populations. Most of the syllable types exhibited low degrees ofpopulation differentiation and differred in spatial distribution patterns with each other.Population divergence in two communication syllable types (QCFs-lDFM and pPFM-sHFM)was correlated with the variation in forearm length. Additionally, a significant relationshipwas found between acoustic and geographical and latitudinal distances for syllableuPFM-uMFM-bUFM, and between nSSR based genetic distance and acoustic distance forsyllable uMFM-bUFM. It was also found that acoustic distance of syllable bUFM-TCF wascorrelated with nSSR based genetic distance and variation in sound transmission rate inhabitat. The population differences in another two syllables (QCFs-cUFM and uPFM train)were significantly correlated with variation in longitude and latitude, respectively. There wasan insignificant relationship between the remaining six syllables and the variables assessed. These results suggest that indirect and direct ecological selection, cultural drift and geneticdrift have contributed partly to the geographical variation in communication sounds of H.armiger.The population differences in echolocation pulses are significantly correlated with thosein two communication syllable types (QCFs-lDFM and pPFM-sHFM). Call frequencies aresignificantly and positively correlated among these three sounds. In addition, the maximumand minimum frequencies of echolocation pulses are significantly and positively correlatedwith those of another two communication call types (bUFM-TCF and uMFM-bUFM),respectively.In summary, both echolocation and communication vocalizations of H. armiger variedsignificantly across populations in China. Population divergence in echolocationvocalizations was driven by morphological variation and geographical distance isolation, i.e.,indirect ecological selection and cultural drift, supporting the epiphenomenon hypothesis andcultural drift hypothesis. Morphological variation, geographical distance, geneticdifferentiation, and variation in sound transmission rate in habitat, latitude, and longitudehave contributed to the geographical variation in seven communication call types, supportingthe epiphenomenon, cultural drift, genetic drift, and acoustic adaptation hypotheses. Theco-variation between echolocation and some of communication vocalizations suggests thatphenotypic traits with distinct functions do not necessarily differ in their spatial distributionpatterns, and that they might vary in concordance geographically when driven by the sameevolutionary forces. To my best knowledge, this is the first integrative study to comparativelyexplore the patterns and causes of geographical variation in echolocation and communicationsignals. It is also the first comprehensive study on the geographical variation ofcommunication vocalizations in bats. This study has enriched the contents of studies onacoustic geographical variation, and has improved our understanding not only of theevolutionary processes driving population divergence in animal acoustic signals but also ofthe relationships between phenotypic functions and patterns of geographical variation.