Body Size Predicts Echolocation Call Peak Frequency Better than Gape Height in Vespertilionid Bats

Correlated evolution between body size and echolocation in bats (order Chiroptera)

BACKGROUND

Body size and echolocation call frequencies are related in bats. However, it is unclear if this allometry applies to the entire clade. Differences have been suggested between nasal and oral emitting bats, as well as between some taxonomic families. Additionally, the scaling of other echolocation parameters, such as bandwidth and call duration, needs further testing. Moreover, it would be also interesting to test whether changes in body size have been coupled with changes in these echolocation parameters throughout bat evolution. Here, we test the scaling of peak frequency, bandwidth, and call duration with body mass using phylogenetically informed analyses for 314 bat species. We specifically tested whether all these scaling patterns differ between nasal and oral emitting bats. Then, we applied recently developed Bayesian statistical techniques based on large-scale simulations to test for the existence of correlated evolution between body mass and echolocation.

RESULTS

Our results showed that echolocation peak frequencies, bandwidth, and duration follow significant allometric patterns in both nasal and oral emitting bats. Changes in these traits seem to have been coupled across the laryngeal echolocation bats diversification. Scaling and correlated evolution analyses revealed that body mass is more related to peak frequency and call duration than to bandwidth. We exposed two non-exclusive kinds of mechanisms to explain the link between size and each of the echolocation parameters.

CONCLUSIONS

The incorporation of Bayesian statistics based on large-scale simulations could be helpful for answering macroevolutionary patterns related to the coevolution of traits in bats and other taxonomic groups.

Scale-dependent influences of environmental, historical, and spatial processes on taxonomic and functional beta diversity of Japanese bat assemblages

This study investigated the relative influences of environmental, spatial, and historical factors, including the island-specific history of land connectivity, on bat assemblages in the Japanese Archipelago. We collected bat distribution data from 1408 studies and assigned them to Japan's First Standard Grid (approximately 6400 km2). Japanese bat assemblages were analyzed at two scales: the entire Japanese Archipelago comprised 16 islands and exclusively the four main islands. At first, we calculated taxonomic and functional total beta diversity (β total) by Jaccard pairwise dissimilarity and then divided this into turnover (β repl) and richness-difference (β rich) components. We conducted hierarchical clustering of taxonomic beta diversity to examine the influence of the two representative sea straits, Tsugaru and Tokara, which are considered biogeographical borders. Variation partitioning was conducted to evaluate the relative effects of the three factors on the beta diversity. Clustering revealed that the Tokara Strait bordered the two major clades; however, the Tsugaru Strait did not act as a biogeographical border for bats. In the variation partitioning, shared fraction between spatial and historical factors significantly explained taxonomic and functional β total and taxonomic β repl at the entire archipelago scale, but not at the four main islands scale extending only Tsugaru Strait but not Tokara Strait. Pure environmental factors significantly explained functional β total at both scales and taxonomic β total only at the four main islands scale. These results suggest that spatial and historical factors are more pronounced in biogeographical borders, primarily structuring assemblage composition at the entire archipelago scale, especially in taxonomic dimension. However, current environmental factors primarily shape the assemblage composition of Japanese bats at the main island scale. The difference in results between the two scales highlights that the primary processes governing assemblages of both dimensions depend on the quality of the dispersal barriers between terrestrial and aquatic barriers for bats.

Giant panda (Ailuropoda melanoleuca) neonates use broadband calls to communicate with their mothers

Infant call structure should have evolved to elicit maximum maternal attention and investment. Neonates of giant pandas produce three types of vocalizations reported to be vitally important in the context of mother-infant communications. However, how cubs, 0-15 days old, communicate with their mothers to elicit maternal care remains unknown. We analyzed 12 different call parameters of 3475 squawks, 1355 squalls, and 491 croaks from 11 captive giant panda (Ailuropoda melanoleuca) neonates from age 0 to 15 days. In playback experiments, we also tested whether mothers could detect ultrasound. Our results show that neonates use broadband calls with ultrasonic frequencies up to 65 kHz to convey information about their physiological needs and to attract maternal care. In playback experiments, we tested if mothers reacted differently to broadband calls (BBC) than to artificially altered calls that included only frequencies <20 kHz (AUDC) or calls that included only frequencies >20 kHz (USC). Playback confirmed that, although adult females responded significantly less often to USC, BBC than to or AUDC, they could detect USC, BBC and generally made appropriate behavioral responses, indicating a potential benefit for neonates to utilize ultrasonic and broadband frequencies. Our findings provide a new insight into mother-infant communication in giant pandas and will be helpful for reducing the mortality of cubs, younger than 1 month old, in captivity.

Ecomorphological correlates of inner and middle ear anatomy within phyllostomid bats

Echolocation is the primary sense used by most bats to navigate their environment. However, the influence of echolocating behaviors upon the morphology of the auditory apparatus remains largely uninvestigated. While it is known that middle ear ossicle size scales positively with body mass across mammals, and that peak call frequency scales negatively with body mass among bats, there are still large gaps in our understanding of the degree to which allometry or ecology influences the morphology of the chiropteran auditory apparatus. To investigate this, we used μCT datasets to quantify three morphological components of the inner and middle ear: ossicle size, ossicle shape, and cochlear spirality. These data were collected across 27 phyllostomid species, spanning a broad range of body sizes, habitats, and dietary categories, and the relationships between these variables and ear morphology were assessed using a comparative phylogenetic approach. Ossicle size consistently scaled with strong negative allometry relative to body mass. Cochlear spirality was significantly (p = .025) associated with wing aspect ratio (a proxy for habitat use) but was not associated with body mass. From a morphological perspective, the malleus and incus exhibited some variation in kind with diet and call frequency, while stapes morphology is more closely tied to body size. Future work will assess these relationships within other chiropteran lineages, and investigate potential morphological differences in the middle and inner ear of echolocating-vs-non-echolocating taxa.

Morphological specialization to nectarivory in Phyllostomus discolor (Wagner, 1843) (Chiroptera: Phyllostomidae)

Dedicated nectarivory is a derived feeding habit that requires specialized cranial and soft-tissue morphologies to extract nectar from flowers. Nectarivory has evolved many times in terrestrial vertebrates, and in four bat families (Pteropodidae, Phyllostomidae, Vespertilionidae, and Mystacinidae). Within phyllostomids, specializations to nectarivory have been well documented in two subfamilies, Glossophaginae and Lonchophyllinae. However, nectarivory has also evolved independently in the genus Phyllostomus (subfamily Phyllostominae). Since Phyllostomus species have an omnivorous diet with a high consumption of nectar, they can be used to explore the basic morphological modifications linked to evolving a nectarivorous habit. Here, we focused on describing and comparing the morphological features potentially associated with nectarivory in Phyllostomus discolor. We present the first detailed tongue and palate morphological descriptions for P. discolor and perform skull morphometric analysis including 10 species. We found hair-like papillae on the tongue of P. discolor, a convergent feature with Glossophaginae and nectarivorous Pteropodids; these papillae likely confer an advantage when feeding on nectar. P. discolor does not show skull morphological features characteristic of nectarivorous bats, such as a long and narrow snout. We pose that the consumption of a variety of food, such as hard insects and fruits, and the large size of P. discolor relative to specialized nectarivores may create trade-offs against morphological specialization of the skull towards nectarivory. In contrast, a long and mobile tongue with hair-like papillae may be an evolutionary solution for nectar extraction that does not have a major impact on this species' ability to feed on other resources.

Mormoopid bats from Brazil: updates on the geographic distribution of three species and their echolocation calls

Mormoopids are a small group of insectivorous bats largely distributed from the southwestern United States throughout Central and South America. They occupy a wide variety of habitats, and in Brazil have usually been associated with habitats in the Amazon, Cerrado, or Caatinga biomes. Nevertheless, most of the information compiled so far to infer their distributional limits is based on roosting colonies occasionally found in caves or on inventories using bat mist netting, which is known to be an ineffective method for capturing aerial insectivorous bats. In this contribution, we present new occurrence records of mormoopid bats based on acoustic surveys in the Caatinga and Cerrado biomes and make an extensive literature review to provide an up-to-date distribution of these bats in Brazil. We additionally describe important parameters of the echolocation calls of mormoopids across the geographical scope of our study, contrasting our data with published information to provide a better overview of the intraspecific acoustic variation of these bat species. Our acoustic data reveal a larger area of occurrence of mormoopids in Brazil than previously known, confirming new records for two states.

Wings of fringed fruit-eating bats (Artibeus fimbriatus) are highly integrated biological aerofoils from perspectives of secondary sexual dimorphism, allometry and modularity

Phenotypic variability is ubiquitous. This is especially true in bats, where families such as Phyllostomidae encompass as much phenotypic variability as some entire orders of mammals. Typically, phenotypic variability is characterized based on cranial morphology, with studies of other functionally important aspects of the phenotype, such as legs, feet and wings, being less frequent. We examined patterns of secondary sexual dimorphism and allometry of wing elements of the fringed fruit-eating bat (Artibeus fimbriatus) and examined, for the first time, the modularity of bat wings. Patterns were based on 13 wing measurements taken from 21 females and 15 males from eastern Paraguay. From a multivariate perspective, A. fimbriatus exhibited significant secondary sexual dimorphism. Females were larger than males for all 13 wing characteristics, with significant differences involving the last phalanx of the fourth and fifth digits. Female wings were also relatively larger than male wings from a multivariate perspective, as was the last phalanx of the fourth and fifth digits, after adjusting for wing size based on forearm length. Wing elements were highly variable regarding allometric relationships, with some exhibiting no allometric patterns and others exhibiting isometry or hyperallometry, depending on the element. Wings exhibited significant modularity, with metacarpals, proximal phalanges and distal phalanges each representing a discrete module. The wings of A. fimbriatus exhibit substantive patterns of dimorphism, allometry and modularity. Although the big mother hypothesis is a strong theoretical construct to explain wing dimorphism, there is not yet any sound theoretical basis for the patterns of allometry and modularity of the wing. Further investigation is required to understand the determinants of variation in wing morphology.

Atmospheric humidity affects global variation of bat echolocation via indirect effects

The peak frequency of bat echolocation is a species-specific functional trait linked to foraging ecology. It is tailored via evolution to suit conditions within the distribution range of each species, but the evolutionary drivers are not yet well-understood. Global patterns of humidity correlate with many aspects of bat ecology. We hypothesized that atmospheric absolute humidity could explain global peak frequency variation directly and indirectly via increasing species body size and bat species richness. These hypotheses were tested using Bayesian phylogenetic path analysis on 226 tropical and subtropical bat species. In line with our predictions, we found a positive total effect of humidity on peak frequency, which was dominated by the positive indirect effects via body size and bat species richness. We did not observe the negative direct effect of humidity on peak frequency, which was hypothesized based on atmospheric attenuation of sound. In line with our expectations, excluding the predominantly clutter foraging bat families from our dataset downplayed the importance of the richness-mediated route. To conclude, our findings suggest that indirect effects, owing to ecology and biogeography of bat taxa, play a major role in the global relationship between peak frequency and atmospheric humidity.

Ecosystems Services Provided by Bats Are at Risk in Brazil

Ecosystem services (ES) are essential for human society worldwide. ES originate from ecological processes commonly occurring in well-preserved regions. Bats play an essential role in providing such services, primarily insect suppression, plant pollination, and seed dispersal. Human activities have affected Earth’s systems, compromising species and ecosystems and, consequently, the ES provision. Brazil is a country with many bat species but is also one of the world’s leaders in deforestation. Here we aimed to identify regions with high potential for bats ecosystem services provision, assuming that the predicted presence of the species represents the existence of the services. First, we used a Maximum Entropy algorithm to model the distribution of 128 bat species, which correspond to 71% of the Brazilian species. We classify all species into 10 different groups, which resulted from a combination of three body sizes and four predominant trophic guilds (i.e., frugivores, insectivores, nectarivores, and carnivores). The guilds were associated with services of seed dispersion, pest control, pollination, and animal control. Then, we created a 0.5 × 0.5-degree grid to represent an index of ES per guild, which is defined by the sum of the product of the bat’s size weight (1, 2, or 3) by the area occupied of each species in each cell. For comparison, the index was normalized and scaled from 0 to 1. Finally, we used a map of current land use to compare the effects of natural area suppression on the provision of ES in each cell. Our results indicate a substantial reduction in the provision of ES by bats in extensive parts of the central and eastern parts of Brazil, but changes in ES varies among biomes. While the loss of species is an important factor affecting the provision of ES in the Atlantic Forest and the Cerrado, the reduction of species occurrence is most important factor in Amazonia, Caatinga, or Pantanal regions. We suggest that degraded area restoration should be promoted in areas with high ES values and areas near cities and croplands and that a precautionary approach of promoting the conservation of high provider richness should be applied to protect the continuation of bat’s ES.

Hearing sensitivity: An underlying mechanism for niche differentiation in gleaning bats

Tropical ecosystems are known for high species diversity. Adaptations permitting niche differentiation enable species to coexist. Historically, research focused primarily on morphological and behavioral adaptations for foraging, roosting, and other basic ecological factors. Another important factor, however, is differences in sensory capabilities. So far, studies mainly have focused on the output of behavioral strategies of predators and their prey preference. Understanding the coexistence of different foraging strategies, however, requires understanding underlying cognitive and neural mechanisms. In this study, we investigate hearing in bats and how it shapes bat species coexistence. We present the hearing thresholds and echolocation calls of 12 different gleaning bats from the ecologically diverse Phyllostomid family. We measured their auditory brainstem responses to assess their hearing sensitivity. The audiograms of these species had similar overall shapes but differed substantially for frequencies below 9 kHz and in the frequency range of their echolocation calls. Our results suggest that differences among bats in hearing abilities contribute to the diversity in foraging strategies of gleaning bats. We argue that differences in auditory sensitivity could be important mechanisms shaping diversity in sensory niches and coexistence of species.

Functional correlates of skull shape in Chiroptera: feeding and echolocation adaptations

Morphological, functional, and behavioral adaptations of bats are among the most diverse within mammals. A strong association between bat skull morphology and feeding behavior has been suggested previously. However, morphological variation related to other drivers of adaptation, in particular echolocation, remains understudied. We assessed variation in skull morphology with respect to ecology (diet and emission type) and function (bite force, masticatory muscles and echolocation characteristics) using geometric morphometrics and comparative methods. Our study suggests that variation in skull shape of 10 bat families is the result of adaptations to broad dietary categories and sound emission types (oral or nasal). Skull shape correlates with echolocation parameters only in a subsample of insectivorous species, possibly because they (almost) entirely rely on this sensory system for locating and capturing prey. Insectivores emitting low frequencies are characterized by a ventrally tilted rostrum, a trait not associated with feeding parameters. This result questions the validity of a trade-off between feeding and echolocation function. Our study advances understanding of the relationship between skull morphology and specific features of echolocation and suggests that evolutionary constraints due to echolocation may differ between different groups within the Chiroptera.

How Loud Can you go? Physical and Physiological Constraints to Producing High Sound Pressures in Animal Vocalizations

Sound is vital for communication and navigation across the animal kingdom and sound communication is unrivaled in accuracy and information richness over long distances both in air and water. The source level (SL) of the sound is a key factor in determining the range at which animals can communicate and the range at which echolocators can operate their biosonar. Here we compile, standardize and compare measurements of the loudest animals both in air and water. In air we find a remarkable similarity in the highest SLs produced across the different taxa. Within all taxa we find species that produce sound above 100 dBpeak re 20 μPa at 1 m, and a few bird and mammal species have SLs as high as 125 dBpeak re 20 μPa at 1 m. We next used pulsating sphere and piston models to estimate the maximum sound pressures generated in the radiated sound field. These data suggest that the loudest species within all taxa converge upon maximum pressures of 140–150 dBpeak re 20 μPa in air. In water, the toothed whales produce by far the loudest SLs up to 240 dBpeak re 1 μPa at 1 m. We discuss possible physical limitations to the production, radiation and propagation of high sound pressures. Furthermore, we discuss physiological limitations to the wide variety of sound generating mechanisms that have evolved in air and water of which many are still not well-understood or even unknown. We propose that in air, non-linear sound propagation forms a limit to producing louder sounds. While non-linear sound propagation may play a role in water as well, both sperm whale and pistol shrimp reach another physical limit of sound production, the cavitation limit in water. Taken together, our data suggests that both in air and water, animals evolved that produce sound so loud that they are pushing against physical rather than physiological limits of sound production, radiation and propagation.

Pup ultrasonic isolation calls of six gerbil species and the relationship between acoustic traits and body size

Among Gerbillinae rodents, ultrasonic calls of adults of small-sized species are typically higher frequency than those of adults of large-sized species. This study investigates whether a similar relationship can be found in pups of six gerbil species (Dipodillus campestris, Gerbillus perpallidus, Meriones unguiculatus, Meriones vinogradovi, Sekeetamys calurus and Pachyuromys duprasi). We compared the average values of acoustic variables (duration, fundamental and peak frequency) of ultrasonic calls (20 calls per pup, 1200 in total) recorded from 6- to 10-day-old pups (10 pups per species, 60 in total) isolated for 2 min at 22°C and then weighed and measured for body variables. The longest calls (56 ± 33 ms) were found in the largest species, and the highest frequency calls (74.8 ± 5.59 kHz) were found in the smallest species. However, across species, call duration (ranging from 56 to 159 ms among species) did not display a significant relationship with pup body size; and, among frequency variables, only the minimum fundamental frequency depended on pup body size. Discriminant analysis assigned 100% of calls to the correct species. The effect of species identity on the acoustics was stronger than the effect of body size. We discuss these results with the hypotheses of acoustic adaptation, social complexity, hearing ranges and phylogeny.

Body mass explains digestive traits in small vespertilionid bats

Bats are unique among mammals in that they have evolved the capacity to fly. This has generated strong selective pressure on the morphology and function of their digestive system. Given that in bats intestinal length and nominal surface-area are proportional to body mass, this trait importantly relates to explaining some of their digestive characteristics. We described the relationship between digestive traits and body mass of four species of bats of the family Vespertilionidae living in a montane ecosystem in central Mexico. We calculated food transit time, apparent dry matter digestibility, and defecation rate in feeding trials under captive conditions. We also: (1) built a model of the relationship between digestive traits and body mass to determine if this association was consistent within the members of the family Vespertilionidae, and (2) mapped these traits along the phylogeny to explore how digestive characteristics may have evolved. In our feeding trials, body mass was positively related to transit time and negatively related to apparent dry matter digestibility. The model predicted accurately the transit time in bats with body mass < 20 g. The phylogenetic approach suggested that over the evolutionary history of the family, transit time decreased as digestibility increased. Because of the results obtained here, it is likely that for most bats of the family Vespertilionidae, adaptations in digestive traits to process food have followed evolutionary changes in their body mass. We discuss these findings in a physiological and ecological context.

Hearing sensitivity and amplitude coding in bats are differentially shaped by echolocation calls and social calls

Differences in auditory perception between species are influenced by phylogenetic origin and the perceptual challenges imposed by the natural environment, such as detecting prey- or predator-generated sounds and communication signals. Bats are well suited for comparative studies on auditory perception since they predominantly rely on echolocation to perceive the world, while their social calls and most environmental sounds have low frequencies. We tested if hearing sensitivity and stimulus level coding in bats differ between high and low-frequency ranges by measuring auditory brainstem responses (ABRs) of 86 bats belonging to 11 species. In most species, auditory sensitivity was equally good at both high- and low-frequency ranges, while amplitude was more finely coded for higher frequency ranges. Additionally, we conducted a phylogenetic comparative analysis by combining our ABR data with published data on 27 species. Species-specific peaks in hearing sensitivity correlated with peak frequencies of echolocation calls and pup isolation calls, suggesting that changes in hearing sensitivity evolved in response to frequency changes of echolocation and social calls. Overall, our study provides the most comprehensive comparative assessment of bat hearing capacities to date and highlights the evolutionary pressures acting on their sensory perception.

Potential foraging niche release in insectivorous bat species relatively unaffected by white-nose syndrome?

White-nose syndrome (WNS) has rendered four of Ontario’s species endangered, while leaving the other four species relatively unaffected. The causes and extent of the declines have been widely studied. The influence on remaining bat species has not. Comparing acoustic data recorded ∼10 years apart, we evaluated how species in southeastern Ontario, Canada, use different foraging habitats pre- and post-WNS detection. We observed activity declines in now-endangered species over open fields (small-footed myotis, Myotis leibii (Audubon and Bachman, 1842); little brown bat, Myotis lucifugus (Le Conte, 1831); northern myotis, Myotis septentrionalis (Trouessart, 1897); tricolored bat, Perimyotis subflavus (F. Cuvier, 1832)) and speculate that the reduction of the once most common species (M. lucifugus) may have resulted in other species searching for prey in habitat once dominated by M. lucifugus. That is, these changes may have allowed greater presence in open field and clutter or edge environments by the big brown bat (Eptesicus fuscus (Palisot de Beauvois, 1796)) and three migratory species (silver-haired bat, Lasionycteris noctivagans (Le Conte, 1831); red bat, Lasiurus borealis (Müller, 1776); hoary bat, Lasiurus cinereus (Palisot de Beauvois, 1796)). However, our results also suggest that (i) while the decline of most resident bat species due to WNS may have relaxed competition for relatively unaffected species in some, but not all habitats, that (ii) sensory and biomechanical constraints may limit prey exploitation by these less-affected bat species in these habitats.

Does evolution of echolocation calls and morphology in Molossus result from convergence or stasis?

Although many processes of diversification have been described to explain variation of morphological traits within clades that have obvious differentiation among taxa, not much is known about these patterns in complexes of cryptic species. Molossus is a genus of bats that is mainly Neotropical, occurring from the southeastern United States to southern Argentina, including the Caribbean islands. Molossus comprises some groups of species that are morphologically similar but phylogenetically divergent, and other groups of species that are genetically similar but morphologically distinct. This contrast allows investigation of unequal trait diversification and the evolution of morphological and behavioural characters. In this study, we assessed the role of phylogenetic history in a genus of bat with three cryptic species complexes, and evaluated if morphology and behavior are evolving concertedly. The Genotype by Sequence genomic approach was used to build a species-level phylogenetic tree for Molossus and to estimate the ancestral states of morphological and echolocation call characters. We measured the correlation of phylogenetic distances to morphological and echolocation distances, and tested the relationship between morphology and behavior when the effect of phylogeny is removed. Morphology evolved via a mosaic of convergence and stasis, whereas call design was influenced exclusively through local adaptation and convergent evolution. Furthermore, the frequency of echolocation calls is negatively correlated with the size of the bat, but other characters do not seem to be evolving in concert. We hypothesize that slight variation in both morphology and behaviour among species of the genus might result from niche specialization, and that traits evolve to avoid competition for resources in similar environments.

The braincase of

We describe in detail three braincases of the ankylosaur Bissektipelta archibaldi from the Late Cretaceous (Turonian) of Uzbekistan with the aid of computed tomography, segmentation, and 3D modeling. Bissektipelta archibaldi is confirmed as a valid taxon and attributed to Ankylosaurinae based on the results of a phylogenetic analysis. The topographic relationships between the elements forming the braincase are determined using a newly referred specimen with preserved sutures, which is an exceedingly rare condition for ankylosaurs. The mesethmoid appears to be a separate ossification in the newly referred specimen ZIN PH 281/16. We revise and discuss features of the neurocranial osteology in Ankylosauria and propose new diagnostic characters for a number of its subclades. We present a 3D model of the braincase vasculature of Bissektipelta and comment on vascular patterns of armored dinosaurs. A complex vascular network piercing the skull roof and the wall of the braincase is reported for ankylosaurs for the first time. We imply the presence of a lepidosaur-like dorsal head vein and the venous parietal sinus in the adductor cavity of Bissektipelta. We suggest that the presence of the dorsal head vein in dinosaurs is a plesiomorphic diapsid trait, and extant archosaur groups independently lost the vessel. A study of two complete endocranial casts of Bissektipelta allowed us to compare endocranial anatomy within Ankylosauria and infer an extremely developed sense of smell, a keen sense of hearing at lower frequencies (100–3000 Hz), and the presence of physiological mechanisms for precise temperature control of neurosensory tissues at least in derived ankylosaurids.

Bat sonar and wing morphology predict species vertical niche

The use of echolocation allows insectivorous bats to access unique foraging niches by locating obstacles and prey with ultrasounds in complete darkness. To avoid interspecific competition, it is likely that sonar features and wing morphology co-evolved with species vertical distribution, but due to the technical difficulties of studying flight in the vertical dimension, this has never been demonstrated with empirical measurements. The authors equipped 48 wind masts with arrays of two microphones and located the vertical distribution of a community of 19 bat species and two species groups over their annual activity period (>8000 nights). The authors tested the correlation between the proportion of flights at height and the acoustic features of bat calls as well as their wing morphology. The authors found that call peak frequency and bandwidth are good predictors of bat use of the vertical space regardless of their acoustic strategies (i.e., gleaning, hawking, or detecting prey flutter). High wing aspect ratios and high wing loadings were associated with high proportions of time spent at height, confirming hypotheses from the literature.

Coexistence of two sympatric cryptic bat species in French Guiana: insights from genetic, acoustic and ecological data

Background

The distinction between lineages of neotropical bats from the Pteronotus parnellii species complex has been previously made according to mitochondrial DNA, and especially morphology and acoustics, in order to separate them into two species. In these studies, either sample sizes were too low when genetic and acoustic or morphological data were gathered on the same individuals, or genetic and other data were collected on different individuals. In this study, we intensively sampled bats in 4 caves and combined all approaches in order to analyse genetic, morphologic, and acoustic divergence between these lineages that live in the same caves in French Guiana.

Results

A multiplex of 20 polymorphic microsatellite markers was developed using the 454-pyrosequencing technique to investigate for the first time the extent of reproductive isolation between the two lineages and the population genetic structure within lineages. We genotyped 748 individuals sampled between 2010 and 2015 at the 20 nuclear microsatellite loci and sequenced a portion of the cytochrome c oxydase I gene in a subset of these. Two distinct, non-overlapping haplogroups corresponding to cryptic species P. alitonus and P. rubiginosus were revealed, in accordance with previous findings. No spatial genetic structure between caves was detected for both species. Hybridization appeared to be quite limited (0.1–4%) using microsatellite markers whereas introgression was more common (7.5%) and asymmetric for mitochondrial DNA (mtDNA).

Conclusions

The extremely low rate of hybridization could be explained by differences in life cycle phenology between species as well as morphological and acoustical distinction between sexes in one or the other species. Taken together, these results add to our growing understanding of the nature of species boundaries in Pteronotus parnelli, but deserve more in-depth studies to understand the evolutionary processes underlying asymmetric mtDNA introgression in this group of cryptic species.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1289-8) contains supplementary material, which is available to authorized users.

Body size information in large-scale acoustic bat databases

Background

Citizen monitoring programs using acoustic data have been useful for detecting population and community patterns. However, they have rarely been used to study broad scale patterns of species traits. We assessed the potential of acoustic data to detect broad scale patterns in body size. We compared geographical patterns in body size with acoustic signals in the bat species Pipistrellus pipistrellus. Given the correlation between body size and acoustic characteristics, we expected to see similar results when analyzing the relationships of body size and acoustic signals with climatic variables.

Methods

We assessed body size using forearm length measurements of 1,359 bats, captured by mist nets in France. For acoustic analyses, we used an extensive dataset collected through the French citizen bat survey. We isolated each bat echolocation call (n = 4,783) and performed automatic measures of signals, including the frequency of the flattest part of the calls (characteristic frequency). We then examined the relationship between forearm length, characteristic frequencies, and two components resulting from principal component analysis for geographic (latitude, longitude) and climatic variables.

Results

Forearm length was positively correlated with higher precipitation, lower seasonality, and lower temperatures. Lower characteristic frequencies (i.e., larger body size) were mostly related to lower temperatures and northern latitudes. While conducted on different datasets, the two analyses provided congruent results.

Discussion

Acoustic data from citizen science programs can thus be useful for the detection of large-scale patterns in body size. This first analysis offers a new perspective for the use of large acoustic databases to explore biological patterns and to address both theoretical and applied questions.

3D quantitative comparative analysis of long bone diaphysis variations in microanatomy and cross-sectional geometry

Long bone inner structure and cross-sectional geometry display a strong functional signal, leading to convergences, and are widely analyzed in comparative anatomy at small and large taxonomic scales. Long bone microanatomical studies have essentially been conducted on transverse sections but also on a few longitudinal ones. Recent studies highlighted the interest in analyzing variations of the inner structure along the diaphysis using a qualitative as well as a quantitative approach. With the development of microtomography, it has become possible to study three-dimensional (3D) bone microanatomy and, in more detail, the form-function relationships of these features. This study focused on the selection of quantitative parameters to describe in detail the cross-sectional shape changes and distribution of the osseous tissue along the diaphysis. Two-dimensional (2D) virtual transverse sections were also performed in the two usual reference planes and results were compared with those obtained based on the whole diaphysis analysis. The sample consisted in 14 humeri and 14 femora of various mammalian taxa that are essentially terrestrial. Comparative quantitative analyses between different datasets made it possible to highlight the parameters that are strongly impacted by size and phylogeny and the redundant ones, and thus to estimate their relevance for use in form-function analyses. The analysis illustrated that results based on 2D transverse sections are similar for both sectional planes; thus if a strong bias exists when mixing sections from the two reference planes in the same analysis, it would not problematic to use either one plane or the other in comparative studies. However, this may no longer hold for taxa showing a much stronger variation in bone microstructure along the diaphysis. Finally, the analysis demonstrated the significant contribution of the parameters describing variations along the diaphysis, and thus the interest in performing 3D analyses; this should be even more fruitful for heterogeneous diaphyses. In addition, covariation analyses showed that there is a strong interest in removing the size effect to access the differences in the microstructure of the humerus and femur. This methodological study provides a reference for future quantitative analyses on long bone inner structure and should make it possible, through a detailed knowledge of each descriptive parameter, to better interpret results from the multivariate analyses associated with these studies. This will have direct implications for studies in vertebrate anatomy, but also in paleontology and anthropology.

Bats are still not birds in the digital era: echolocation call variation and why it matters for bat species identification

The recording and analysis of echolocation calls are fundamental methods used to study bat distribution, ecology, and behavior. However, the goal of identifying bats in flight from their echolocation calls is not always possible. Unlike bird songs, bat calls show large variation that often makes identification challenging. The problem has not been fully overcome by modern digital-based hardware and software for bat call recording and analysis. Besides providing fundamental insights into bat physiology, ecology, and behavior, a better understanding of call variation is therefore crucial to best recognize limits and perspectives of call classification. We provide a comprehensive overview of sources of interspecific and intraspecific echolocation call variations, illustrating its adaptive significance and highlighting gaps in knowledge. We remark that further research is needed to better comprehend call variation and control for it more effectively in sound analysis. Despite the state-of-art technology in this field, combining acoustic surveys with capture and roost search, as well as limiting identification to species with distinctive calls, still represent the safest way of conducting bat surveys.