Browsing by Author "Bastian, Anna"
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- ItemOpen AccessBehavioural evidence for the perception of individual identity and gender via the echolocation calls of a high duty cycle bat, Rhinolophus clivosus(2015) Finger, Nikita Maxine; Jacobs, David S; Bastian, AnnaDifferent cognitive processes underlie the perception of vocalizations in many mammals, including humans. This perception now extends to a highly specialized form of sonar called echolocation. In habituation-dishabituation experiments, a high duty cycle echolocating bat, Rhinolophus clivosus, dishabituated significantly when echolocation calls of a different gender or individual were played to the habituation. Strong individual and gender signatures but weak geographic signatures were found in both the CF and FM components of their echolocation calls. In the individual discrimination trials reactions were more pronounced to an individual that was less acoustically similar to the habituation than to one that was more similar. Bats reacted to playbacks with a variety of social behaviours. Prior to the analysis of the experiment an ethogram was done on three groups of captive R. clivosus bats. This ethogram was used to categorize the behavioural responses of these bats to the acoustic stimuli in the experiments. The reactions to the habituation-dishabituation experiments show bats perceive gender and individual-specific signatures found in their conspecifics echolocation calls. This is the first study to show behavioural evidence for individual discrimination and second to show gender discrimination of echolocation calls in high duty cycle bats. This evidence supports the theory that echolocation, a system thought to have evolved solely for orientation and foraging, has been coopted for intra-specific communication and mate recognition in bats.
- ItemOpen AccessInvestigation of population abundance, distribution, and population linkage of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) on the north and south of Zanzibar using mark-recapture and acoustic methods(2017) St Clair-Hughes, Adam James Victor; Jacobs, David S; Bastian, Anna; Gridley, T; Elwen, SimonPrevious studies, using a variety of methods such as photographic identification, fisheries observer programs, or genetic testing, on Indo-Pacific bottlenose dolphins (Tursiops aduncus) around Zanzibar Island, Tanzania, suggest separate populations around the north and south coasts. However, most research around the island has focused on the south coast, and movement of dolphins around the coastline is poorly understood. Photographic identification data, consisting of dorsal fin images, and acoustic data from dolphin whistles, both collected in 2008, were analysed to examine linkages between north and south Zanzibar. Photographic identification data was applied in a Mark-Recapture framework, using open population models, to generate abundance estimates of 149 (95% CI 128-173) and 120 (95% CI 97-149) individuals for the north and south coasts of Zanzibar respectively. As 16 individuals had moved from the south to the north coast of Zanzibar during the two month study, a combined population estimate of 353 (95% CI 290-430) individuals for Zanzibar Island was also generated. Acoustic analysis of standard whistle parameters was used to investigate whether these learned signals shared features between the putative populations, using whistle data collected in Plettenberg Bay, South Africa as an out-group. Discriminant function analysis of whistle parameters indicated high classification success of whistles recorded from animals in the north location (86.2%), moderate classification success for the outgroup (61.8%), and zero classification success for Zanzibar's south coast population. High misclassification rates for south Zanzibar suggest that these whistles cannot be readily discriminated from those of north Zanzibar. Shared whistle features suggest that learning may take place between individuals moving between localities. Coupled with previous genetic studies, this study suggests female philopatry and male mediated gene flow between the two areas; however, more genetic markers are necessary to test this interpretation. Further work is also necessary to quantify the degree of movement of dolphins around Zanzibar Island, and potential migration into the area, which will assist in developing management plans.
- ItemOpen AccessListening carefully: increased perceptual acuity for species discrimination in multispecies signalling assemblages(Elsevier Ltd., 2015-03-01) Bastian, Anna; Jacobs, David SteveCommunication is a fundamental component of evolutionary change because of its role in mate choice and sexual selection. Acoustic signals are a vital element of animal communication and sympatric species may use private frequency bands to facilitate intraspecific communication and identification of conspecifics (acoustic communication hypothesis, ACH). If so, animals should show increasing rates of misclassification with increasing overlap in frequency between their own calls and those used by sympatric heterospecifics. We tested this on the echolocation of the horseshoe bat, Rhinolophus capensis, using a classical habituation-dishabituation experiment in which we exposed R. capensis from two phonetic populations to echolocation calls of sympatric and allopatric horseshoe bat species (Rhinolophus clivosus and Rhinolophus damarensis) and different phonetic populations of R. capensis. As predicted by the ACH, R. capensis from both test populations were able to discriminate between their own calls and calls of the respective sympatric horseshoe bat species. However, only bats from one test population were able to discriminate between calls of allopatric heterospecifics and their own population when both were using the same frequency. The local acoustic signalling assemblages (ensemble of signals from sympatric conspecifics and heterospecifics) of the two populations differed in complexity as a result of contact with other phonetic populations and sympatric heterospecifics. We therefore propose that a hierarchy of discrimination ability has evolved within the same species. Frequency alone may be sufficient to assess species membership in relatively simple acoustic assemblages but the ability to use additional acoustic cues may have evolved in more complex acoustic assemblages to circumvent misidentifications as a result of the use of overlapping signals. When the acoustic signal design is under strong constraints as a result of dual functions and the available acoustic space is limited because of co-occurring species, species discrimination is mediated through improved sensory acuity in the receiver.
- ItemOpen AccessPhenotypic convergence in genetically distinct lineages of a Rhinolophus species complex (Mammalia, Chiroptera)(Public Library of Science, 2013) Jacobs, David S; Babiker, Hassan; Bastian, Anna; Kearney, Teresa; Eeden, Rowen van; Bishop, Jacqueline MPhenotypes of distantly related species may converge through adaptation to similar habitats and/or because they share biological constraints that limit the phenotypic variants produced. A common theme in bats is the sympatric occurrence of cryptic species that are convergent in morphology but divergent in echolocation frequency, suggesting that echolocation may facilitate niche partitioning, reducing competition. If so, allopatric populations freed from competition, could converge in both morphology and echolocation provided they occupy similar niches or share biological constraints. We investigated the evolutionary history of a widely distributed African horseshoe bat, Rhinolophus darlingi , in the context of phenotypic convergence. We used phylogenetic inference to identify and date lineage divergence together with phenotypic comparisons and ecological niche modelling to identify morphological and geographical correlates of those lineages. Our results indicate that R. darlingi is paraphyletic, the eastern and western parts of its distribution forming two distinct non-sister lineages that diverged ~9.7 Mya. We retain R. darlingi for the eastern lineage and argue that the western lineage, currently the sub-species R . d. damarensis , should be elevated to full species status. R. damarensis comprises two lineages that diverged ~5 Mya. Our findings concur with patterns of divergence of other co-distributed taxa which are associated with increased regional aridification between 7-5 Mya suggesting possible vicariant evolution. The morphology and echolocation calls of R. darlingi and R. damarensis are convergent despite occupying different biomes. This suggests that adaptation to similar habitats is not responsible for the convergence. Furthermore, R. darlingi forms part of a clade comprising species that are bigger and echolocate at lower frequencies than R. darlingi , suggesting that biological constraints are unlikely to have influenced the convergence. Instead, the striking similarity in morphology and sensory biology are probably the result of neutral evolutionary processes, resulting in the independent evolution of similar phenotypes.
- ItemOpen AccessThe role of echolocation in communication in a high duty cycle echolocating bat, Rhinolophus clivosus (Chiroptera: Rhinolophidae): an experimental approach(2016) Raw, Robert; Jacobs, David S; Bastian, AnnaAcoustic communication plays a pivotal role in species recognition across a number of taxa. Species must therefore maintain discrete acoustic signatures to facilitate communication and avoid misidentification. The Acoustic Communication Hypothesis (ACH) thus proposes that in multispecies assemblages, multidimensional acoustic space is partitioned so that each species occupies a discrete acoustic space despite overlap in single parameters (e.g. frequency). Horseshoe bats use echolocation for the purpose of orientation and foraging. However, given the presence of individual and species specific cues in echolocation, it is likely that echolocation also functions to some degree in acoustic communication. This dual function makes echolocation a good model system to investigate the evolution of communication. In support of the ACH recent studies have shown that horseshoe bats are able to discriminate between conspecifics and heterospecifics based on echolocation calls alone even when call frequencies overlap. This suggests that multiple components of echolocation are influential in a bats ability to discriminate between species and indicates a dual function of echolocation in orientation and communication. These multiple components have not until now been identified. Studies have also suggested that preference for echolocation calls in the context of mate choice may influence the evolution of echolocation through sexual selection. Using classical habituation – dishabituation playback experiments, I tested the ability of Geoffroy's horseshoe bat, Rhinolophus clivosus, to discriminate between echolocation calls of heterospecifics with either discrete or overlapping resting frequencies. I subsequently used synthesised calls in which I manipulated individual acoustic parameters, to investigate which call components are involved in discrimination amongst species. Finally, I used a two-alternative choice experiment to investigate preference by R. clivosus to calls of individuals of opposite gender as well as between individuals with high or low body condition during the mating season. Rhinolophus clivosus was able to discriminate readily between echolocation calls with discrete frequencies from different species. When frequencies overlapped, however, the ability of bats to discriminate between species was dependant on additional spectral and temporal components of calls that defined the entire acoustic space occupied by the calls. Consequently, calls that were similar in this multi-parametric acoustic space yielded low levels of discrimination, whereas calls separated in acoustic space yielded high levels of discrimination. This study provides the first experimental evidence of call components, other than frequency, that may play a role in species discrimination and questions earlier reports that bats use echolocation in mate choice. In support of the communicative role of echolocation, bats were also able to discriminate between calls from bats that differed in their body condition, indicating echolocation might represent an honest signal of mate quality and thus a function in mate choice. However, despite this, R. clivosus showed no preference or association based on gender or body condition. The results of this study suggest that despite having the ability to use echolocation to discriminate amongst conspecifics, these bats do not base mate choice on echolocation call components.
- ItemOpen AccessTo seek or speak? Dual function of an acoustic signal limits its versatility in communication(Elsevier Ltd, 2017) Finger, Nikita M; Bastian, Anna; Jacobs, David SThe perception of different attributes of conspecifics is an integral part of intraspecific communication. It can facilitate the recognition of interaction partners or the assessment of potential mates. Acoustic signals can encode fine-scaled information through the interplay of acoustic variability and specificity. A reliable vocal signature is both unique within a class and variable between classes. Therefore, acoustic complexity might be associated with the number of classes to be discriminated. We investigated the assumption that limitations to signal design may affect the communicative functionality of a signal. To do so, we chose a signal with potentially dual functionality which may therefore display such limitations. In bats, echolocation is used primarily for foraging and orientation but there is increasing support for its additional role in communication. An acoustic analysis of echolocation pulses of the bat Rhinolophus clivosus confirmed sex and individual vocal signatures in echolocation pulses. A habituation edishabituation playback experiment suggested that bats perceived these signatures because listening bats clearly discriminated between the sexes (two classes) and between individuals (representatives of a multiclass category), although to different degrees. The simple acoustic structure of these vocalizations provides sufficient specificity for sex discrimination but has limitations for individual discrimination because pulse parameters of individuals increasingly overlapped with increasing group size. We conclude that selection for the primary function of echolocation restricts the acoustic space available for communication. However, we frequently observed echolocation pulses with conspicuous structural modifications. Statistical analyses revealed that these vocalizations yielded increased individual distinctiveness. Such added systematic variation may indicate a communicative function and perhaps a signalling intent of the emitter, although the latter has yet to be tested. The findings suggest that the required specificity for effective communication could be obtained through modification of echolocation variants when adaptations for orientation and foraging constrain the evolution of complex communication signatures.