Variation In Echolocation Calls Research Articles

Divergence in interspecific and intersubspecific gene expression between two closely related horseshoe bats (Rhinolophus)

AbstractClosely related species have been used as representative systems to investigate the genetic mechanisms involved in the early stages of species differentiation. Previous studies have indicated that variation in gene expression might be a sensitive indicator of initial species divergence, although the role of expression divergence, and especially that associated with phenotypic variation remained relatively undefined. For three organs (cochlea, brain, and liver) from two closely related bat species (Rhinolophus siamensis and R. episcopus), the interspecific and intersubspecific gene expression profiles were compared using transcriptomics in this study. Striking organ specificity of expression was observed, and expression profiles exhibited similarities between cochlea and brain tissues. Numerous differentially expressed genes (DEGs) were identified for each organ in the interspecific comparison (cochlea/brain/liver: 1,069/647/692) and intersubspecific comparison (608/528/368). Functional enrichment analysis indicated vital variation in expression related to the immune system, ion activities, neuronal function, and multisensory system regulation in both comparisons. DEGs relevant to the variation in echolocation calls (RF) were found, and some of them were involved in the pivotal patterns of expression variation. The regulation of immune, ion channel, neural activity, and sophisticated sensory functions at the expression level might be key mechanisms in the early species divergence of bats, and the expression variation related to acoustical signal could have played a crucial part. This study expands our knowledge of gene expression and patterns of variation for three key organs to echolocation at both the interspecific and intersubspecific levels. Further, the framework described here provides insight into the genetic basis of phenotypic variation during the incipient stage of species differentiation.

Variation in echolocation calls produced by Myotis velifer (Chiroptera: Vespertilionidae) during postnatal development

This work describes the echolocation pulses produced by Myotis velifer during postnatal development. The aim was to record the changes of these calls during the development of this bat species and investigate the underlying causes. Bat specimens were sampled in El Salitre cave, Morelos, Mexico, during May and June 2016, where juvenile bats were captured and sorted into five age classes. Forearm length was used as reference for offspring growth. Each juvenile bat was induced to fly and the echolocation calls produced were recorded using an ultrasound detector. Six quantitative characteristics of the echolocation pulses of each call were measured, which served as reference to explore the development of this system during growth through a linear regression. A steady increase in the frequency parameters associated with bat growth was observed, coupled with a decrease in the temporal parameters. The final pulse frequency was the only parameter that remained unchanged during postnatal growth. The major changes in the characteristics of echolocation pulses during postnatal growth in M. velifer follow the pattern observed in other species previously studied. These changes are likely related to the development of organs and muscles involved in the emission and reception of sound, and to the learning process involved in the use of this adaptation.

The effects of cultural drift on geographic variation in echolocation calls of the Chinese rufous horseshoe bat (Rhinolophus sinicus)

AbstractDrift, selection, or their combined effects commonly drive geographic variation in traits. Clarifying the relative roles of each process is a long‐standing research goal in evolutionary biology. Acoustic signals of bats are a phenotypic characteristic that plays an important role in social organization and species recognition. We extensively sampled the Chinese rufous horseshoe bat (Rhinolophus sinicus) throughout China and Vietnam and reconstructed a species phylogeny to better understand the patterns and causes of the geographic variation of acoustic signals. Our results showed that the resting frequency (RF) of calls varied with latitude, sex, and distance among different colony locations. RF differences were not correlated with genetic distance (based on only one nuclear locus and the mitochondrial locus), climatic factors (mean annual temperature and mean annual precipitable water), or body size, although differences in calls increased with distance among various populations. This suggests that cultural drift may play more important roles than genetic drift and acoustic adaptation in shaping acoustic differences within regions in R. sinicus.

Behavioural response of the greater horseshoe bat to geographical variation in echolocation calls

The geographical variation in animals’ social acoustical signals can reduce recognition across populations and may thus promote assortative mating, reproductive isolation and speciation. However, the social consequences of geographical variation in acoustical signals serving an ecological function are poorly known. Bat echolocation calls are considered to have a dual function; they are used not only for orientation and foraging but also for communication. In this study, we studied the behavioural response of Rhinolophus ferrumequinum to geographical variation in echolocation calls. Using habituation-dishabituation playback experiments, we found that all tested bats from northeast China exhibited obvious responses after switching playback from their own population to those from central east China and southwest China. Using two-choice playback experiments, we showed that the bats from northeast China responded more strongly to echolocation calls from their own population than to those from central east China. Our results demonstrate that Rhinolophus ferrumequinum is able to discriminate between echolocation calls of its local population and a foreign one and that local echolocation calls are preferred over foreign ones in a two-choice context. This study supports the communicative potential of bat echolocation calls and provides insight into the discrimination ability and behavioural preference of bats with respect to geographical variation in echolocation calls. This study provides behavioural evidence for the communicative role in echolocation calls and indicates that a dual function of echolocation calls exists more commonly in bats. Moreover, this study provides insight into the discrimination ability and preference of bats with respect to frequency variation in echolocation calls and contributes to a better understanding of how geographical evolution in ecological acoustical signals may affect the ability of recognition between populations.

Sensory Drive Mediated by Climatic Gradients Partially Explains Divergence in Acoustic Signals in Two Horseshoe Bat Species, Rhinolophus swinnyi and Rhinolophus simulator

Geographic variation can be an indicator of still poorly understood evolutionary processes such as adaptation and drift. Sensory systems used in communication play a key role in mate choice and species recognition. Habitat-mediated (i.e. adaptive) differences in communication signals may therefore lead to diversification. We investigated geographic variation in echolocation calls of African horseshoe bats, Rhinolophus simulator and R. swinnyi in the context of two adaptive hypotheses: 1) James’ Rule and 2) the Sensory Drive Hypothesis. According to James’ Rule body-size should vary in response to relative humidity and temperature so that divergence in call frequency may therefore be the result of climate-mediated variation in body size because of the correlation between body size and call frequency. The Sensory Drive Hypothesis proposes that call frequency is a response to climate-induced differences in atmospheric attenuation and predicts that increases in atmospheric attenuation selects for calls of lower frequency. We measured the morphology and resting call frequency (RF) of 111 R. simulator and 126 R. swinnyi individuals across their distributional range to test the above hypotheses. Contrary to the prediction of James’ Rule, divergence in body size could not explain the variation in RF. Instead, acoustic divergence in RF was best predicted by latitude, geography and climate-induced differences in atmospheric attenuation, as predicted by the Sensory Drive Hypothesis. Although variation in RF was strongly influenced by temperature and humidity, other climatic variables (associated with latitude and altitude) as well as drift (as suggested by a positive correlation between call variation and geographic distance, especially in R. simulator) may also play an important role.

Choice Experiments Demonstrate that Male Big Brown Bats (Eptesicus fuscus) Prefer Echolocation Calls of High Copulatory Females

It generally is accepted that bats emit ultrasonic vocalizations that function for echolocation purposes as well as for communication. We tested whether male or female big brown bats (Eptesicus fuscus) responded to variation in echolocation calls of the opposite sex in a manner that would suggest calls are used in a mating context. We presented 31 female and 10 male big brown bats with ultrasonic playbacks of differentially mating (i.e., high frequency copulators = HM versus low-frequency copulators = LM) individuals of the opposite sex. We measured 1) which side of the arena each subject selected first (HM versus LM), and 2) duration spent (seconds) on each side of the arena (HM versus LM). For both of these measures (i.e., first choice and duration) male subjects were more likely to select the echolocation calls of HM females, but the same respective tests determined that female subjects did not select echolocation calls of frequently copulating males over calls of infrequently copulating males. These r...

Evidence of Echolocation Call Divergence inHipposideros commersoniSensu Stricto (E. Geoffroy, 1803) from Madagascar and Correlation with Body Size

Previous studies conducted on morphological variation of the endemic Malagasy bat Hipposideros commersoni sensu stricto (Hipposideridae) revealed a north-south morphological cline, with larger individuals present in the north. Little is known about potential sexual differences in the echolocation calls of this species. We captured 59 adult individuals (24 males and 35 females) at different sites spanning the western half of Madagascar, measured their forearm length and recorded echolocation calls. These data were used to examine possible variation in echolocation calls and body size, which showed statistically significant differences. Male H. commersoni have an average forearm length of 93.1 mm and emit calls at 68.6 kHz, while the average measurements for females are 83.9 mm and about 72.9 kHz, respectively. Principal component analysis revealed variation in morphological and bioacoustic parameters, suggesting a high intraspecific variation. Regression analysis of intersexual data showed that females fro...

Variation in echolocation calls of Hipposideros amiger during habituation to a novel, captive environment

Animals alter their behaviour during habituation to novel environments. Echolocating bats exhibit remarkable flexibility in their acoustic signals to sense diverse microhabitats. Previous studies have described intra-individual variation in echolocation calls of bats in different environments, but few studies have systematically quantified these changes in detail. We investigated variation in echolocation call structure of the great leaf-nosed bat,Hipposideros armigerduring habituation to a novel, captive environment. Echolocation calls of free-ranging bats were recorded in the natural habitat and in captivity over a three-week period. We found that bats exhibited significant changes in some call parameters following introduction to the novel captive environment, and some parameters changed continuously over time. We observed plasticity in peak frequency, pulse duration and pulse rate during the captive period. This suggests that variation in echolocation calls of bats in response to a novel captive environment is a progressive process, during which bats adjust echolocation call structure to habituate gradually to their surroundings.

Strong matrilineal structure in common pipistrelle bats (Pipistrellus pipistrellus) is associated with variability in echolocation calls

The ontogeny and heritability of echolocation, an important sense in echolocating bats, is still not completely understood. Intraspecific variation in echolocation calls can be high, although the importance of possible explanatory variables (e.g. age, sex, social groups) remains largely unknown. Echolocation pulse features may vary among maternity roosts and this can theoretically be caused either by intercolony genetic differences or by vocal dialects learned during ontogeny within a roost (or a combination of both). In the present study, we analyzed intraspecific variation in echolocation parameters in relation to genetic structure at bi-parentally inherited microsatellites and maternally inherited mitochondrial (mt)DNA in maternal colonies of Pipistrellus pipistrellus in Central Europe. We found that individual colonies differ significantly in mtDNA, whereas the structure on nuclear markers is almost absent. This suggests a typical temperate bat social structure pattern, with strong sex-biased dispersal (i.e. philopatric females and dispersing males) (up to 92% of males leave their birth place according to our results). However, we show for the first time that genetic differentiation among mtDNA matrilines is associated with significant intercolony echolocation parameter differences. Because the genetic component of echolocation is not likely to be encoded by mtDNA, the results support the hypothesis of maternal echolocation dialect transmission to offspring, and the role of learning in this process is discussed.

Spatial variation in the echolocation calls of the little brown bat (Myotis lucifugus)

We studied spatial variation in echolocation call structure of the little brown bat (Myotis lucifugus (LeConte, 1831)) by analysing calls recorded from free-flying individuals at 1 site in Haida Gwaii, British Columbia, 1 site in Chautaqua, New York, and 20 sites along the Hudson River, New York. We controlled for factors that are often thought to lead to interspecific variation in echolocation calls (habitat, ontogeny, presence of conspecifics, recording techniques, ambient conditions), which allowed us to focus on the effect of spatial scale on call structure. As predicted, we found that at small scales (up to 1 km), there was significant geographic variation, likely owing to roost-specific signatures and group foraging activities. At intermediate scales (2–500 km), we found no differences in call structure, suggesting that populations within this area are part of a single hibernating and breeding population. Finally, echolocation call structure differed at the continental scale (>1000 km) likely because of little genetic exchange among sampled populations. Our results highlight the importance of considering the magnitude of spatial scale when examining variation in echolocation call structure.

Morphological correlates of echolocation frequency in the endemic Cape horseshoe bat, Rhinolophus capensis (Chiroptera: Rhinolophidae)

We investigated intraspecific variation in echolocation calls of the Cape horseshoe bat, Rhinolophus capensis, by comparing echolocation and associated morphological parameters among individuals from three populations of this species. The populations were situated in the center and at the western and eastern limits of the distribution of R. capensis. The latter two populations were situated in ecotones between vegetation biomes. Ecotone populations deviated slightly from the allometric relationship between body size and peak frequency for the genus, and there was no relationship between these variables within R. capensis. Nasal chamber length was the best predictor of peak frequency but not correlated with body size. The evolution of echolocation thus appears to have been uncoupled from body size in R. capensis. Furthermore, females used higher frequencies than males, which imply a potential social role for peak frequency. The differences in peak frequency may have originated from random founder effects and then compounded by genetic drift and/or natural selection. The latter may have acted directly on peak frequency altering skull parameters involved in echolocation independently of body size, resulting in the evolution of local acoustic signatures.

Geographical and individual variation in echolocation calls of the intermediate leaf‐nosed bat, Hipposideros larvatus

AbstractThe cause and significance of variation in echolocation call frequency within hipposiderid bats is not well understood despite an increasing number of allopatric and sympatric examples being documented. We examined variation patterns in the resting frequency (RF) of echolocation calls emitted by the intermediate leaf‐nosed bat, Hipposideros larvatus, on a broad geographical scale. Data mining technology and Kruskal–Wallis test both showed substantial variation with a longitudinal pattern in RF in H. larvatus among colonies, and this variation was associated with geographical distance and not body size. In addition, we found that a high degree of variability between individuals was hidden under the geographical variation. The results support an effect of random cultural drift, and challenge the prey detection hypothesis. Moreover, an acoustic difference among local island colonies may be indicative of a vocal dialect. We found that each colony of H. larvatus seems to maintain a ‘private bandwidth’, which could be used for colony identity and individual communication thus helping individuals and colonies to get a number of fitness benefits.

A taxonomic review of Rhinolophus stheno and R. malayanus (Chiroptera: Rhinolophidae) from continental Southeast Asia: an evaluation of echolocation call frequency in discriminating between cryptic species

The taxon Rhinolophus microglobosus is elevated to specific rank on the basis of clearly defined morphometric and acoustic characters which differentiate it from Rhinolophus stheno. It is recorded from Cambodia for the first time. Rhinolophus malayanus exhibits considerable geographical variation in echolocation calls, with apparently two phonic types: a northern population with lower frequency calls and a predominantly southern population with higher frequencies. However, this acoustic divergence is not reflected in any morphometric divergence, and the taxonomic status of the two phonic populations remains unclear. Discriminating characters of all three species are given, together with distribution data and short ecological summaries. The value of echolocation as an indicator of cryptic species and the zoogeographical implications of the study are briefly discussed.

Variation in the Echolocation Calls of Little Brown Bats (Myotis lucifugus) in Response to Different Habitats

Among different bat species, echolocation call structure varies predictably according to habitat use. Much of this interspecific variation in echolocation calls reflects the physical constraints of sound propagation and echo formation in open versus spatially complex habitats. Bats must use calls that are suitable for detecting obstacles and prey in a particular setting; thus, bats that use similar habitats and catch similar prey produce similar calls. The same can be true for variation in echolocation calls within a single species that uses a variety of habitats. I recorded the echolocation calls and habitat use of a habitat generalist bat, Myotis lucifugus in order to determine whether the echolocation calls of M. lucifugus vary predictably across habitats, and if call variation is the result of individual flexibility in habitat use and echolocation behavior. I found that M. lucifugus used calls with higher frequencies, shorter durations and steeper frequency modulation in cluttered habitats than in open habitats. This type of call is consistent with a short-range target-detection strategy whereas the lower frequencies, longer call durations and shallower frequency modulation of bats in open habitats are consistent with longer-range target detection strategies. Furthermore, radiotelemetry indicated that individuals routinely foraged in different habitats. Taken together, these results suggest that call variation across habitats is the result of individual plasticity in echolocation behavior.

Individual and Group Variation in Echolocation Calls of Big Brown Bats, Eptesicus fuscus (Chiroptera: Vespertilionidae)

Individual and Group Variation in Echolocation Calls of Big Brown Bats, Eptesicus fuscus (Chiroptera: Vespertilionidae)

Effects of Interindividual Variation in Echolocation Calls on Identification of Big Brown and Silver-Haired Bats

Identifying bat species from their calls is a common technique in studies of habitat use. I tested the hypotheses that significant interindividual intraspecific variation exists in the echolocation calls of bats as detected by frequency-divide ultrasonic detectors, and that such variation could greatly affect the accuracy of species identification. I restricted analysis to 2 species that have similar hut reportedly distinguishable calls. There was significant intraspecific variation in 6 variables for each species, and frequency distributions of the 2 species overlapped greatly for all 6 variables; hence, univariate analysis was ineffective at differentiating between species. The best of experienced human observers correctly identified the species for only 70% of 47 call sequences compared to >95% correct classification by discriminant function analysis. Alterations in current methodology can improve accuracy of identification and thus the value of habitat studies and management decisions that rely on such identification.

Sex and age variation in echolocation calls and flight morphology of Daubenton’s Bats Myotis daubentonii

Nous avons etudie la variation des cris d'echolocation et de la morphologie de l'aile du Murin de Daubenton, Myotis dauhentonii, dans l'ouest de la Pologne. Les individus d'un an ou moins emettaient des cris sonar legerement, mais d'une maniere significative, de plus basse frequence que ceux emis par des murins plus âges. Bien qu'une difference sexuelle dans les cris sonar ne se soit pas manifestee, il existait un dimorphisme de la taille corporelle. Les femelles etaient en moyenne plus grandes que les mâles en ce qui concerne l'envergure et la superficie des ailes. La longueur de l'aile comprenant les doigts et celle comprenant les bras etaient toutes deux plus grandes chez les femelles, et celles-ci etaient aussi plus lourdes que les mâles, d'une maniere significative

Hipposideros caffer (Chiroptera: Hipposideridae) in Zimbabwe: morphology and echolocation calls

The results of this study of morphological variation and variation in echolocation calls indicate that only specimens with narrow lateral nasal inflations (=Hipposideros caffer) have been reported from Zimbabwe to date. In both Zambia and Mocambique, single localities yielded both specimens with narrow or wide lateral nasal inflations (nominally, H. caffer and H. ruber, respectively). There are significant differences in echolocation calls between one site in Zimbabwe and another near the Zimbabwe South Africa border that are not paralleled by significant morphological differences.