The marked dextro-dominance causes accentuated morphophysiological variations in the female reproductive organs of the bat Molossus molossus.

Molossus molossus is an insectivorous molossid bat that is important in the control of nocturnal insects. It is the nominal and the most representative species of the family. However, there are few studies about its reproduction. Thus, this study aimed to evaluate variations of its female reproductive organs during the different reproductive phases. Twenty adult females, divided into four sample groups (non-reproductive, early and advanced pregnancy and lactation), were submitted to morphological and morphometric analyses. Results show that the female reproductive system of M. molossus is composed of ovaries, a short bicornuate uterus, slightly convoluted uterine tubes and vagina. The system presents a distinct morphofunctional asymmetry, with a marked dextro-dominance. The right ovaries of all analyzed groups (NON, P1, P2, and LAC) showed follicles at different stages of development, a large number of interstitial glands and a small, but persistent corpus luteum. Ovulation is simple, unilateral and preferential, occurring exclusively in the right ovary. Follicular development in the left ovary usually does not pass the secondary stage. Implantation is fundic and preferential, occurring exclusively in the right uterine horn. The placenta is formed with two distinct chorioallantoic portions, one diffuse endotheliochorial, which covers the entire uterine cavity and regresses in the final stages of pregnancy, and the principal discoidal hemochorial portion, formed in the implantation site. The uterine cervix presents a pseudostratified epithelium, while the vagina has a little keratinized stratified epithelium, which does not accentually vary in the different reproductive stages, but can disrupt and shed in some cases.

Sperm morphology and comparison morphometry measurements of two species of bats, Molossus molossus and Molossops temminckii (Chiroptera: Molossidae).

Sperm morphology is considered a species-specific character and has been used as a tool in the classification of numerous mammalian taxa. Neotropical bats have been poorly studied, and important aspects on sperm morphology have not been elucidated. The aim of the present study was to describe and compare the sperm morphology and morphometry of Molossus molossus and Molossops temminckii. A total of 14 adults specimens were analyzed from the Colección Mamíferos Lillo, Universidad Nacional de Tucumán: five M. molossus and nine M. temminckii. The epididymis were extracted and macerated in Farmer's solution, followed by a coloration with different stains. To carry out the description and morphometric analysis, microphotographs were taken under an optical, epifluorescence, and scanning electron microscope (SEM). A total of 50 sperm from each individual were measured for morphometric analysis. The length and width of the head, midpiece and tail were taken as variables. Sperm from M. molossus and M. temminckii were practically identical, both morphologically and morphometrically. In both species, a distal bulge was observed at the end of the intermediate piece in a percentage greater than 85%. The main characteristics shared between the species were: presence of acrosomal blebs in the upper half of the head of the spermatozoa; cephalic equatorial segment with filiform ornamentations; intermembrane space of head apex wedge-shaped; helical middle piece and annulus at the end of middle piece. In the present study, SEM allowed us to visualize structures, such as acrosomal vesicles, that were not detected with other types of microscopy. RESEARCH HIGHLIGHTS: The similarities in the sperm morphology between M. molossus and M. temminckii were observed with three types of microscopy: optical, epifluorescence and scanning electron, and supported by morphometric and statistical analyses.

An updated synthesis of and outstanding questions in the olfactory and vomeronasal systems in bats: Genetics asks questions only anatomy can answer.

The extensive diversity observed in bat nasal chemosensory systems has been well-documented at the histological level. Understanding how this diversity evolved and developing hypotheses as to why particular patterns exist require a phylogenetic perspective, which was first outlined in the work of anatomist Kunwar Bhatnagar. With the onset of genetics and genomics, it might be assumed that the puzzling patterns observed in the morphological data have been clarified. However, there is still a widespread mismatch of genetic and morphological correlations among bat chemosensory systems. Novel genomic evidence has set up new avenues to explore that demand more evidence from anatomical structures. Here, we outline the progress that has been made in both morphological and molecular studies on the olfactory and vomeronasal systems in bats since the work of Bhatnagar. Genomic data of olfactory and vomeronasal receptors demonstrate the strong need for further morphological sampling, with a particular focus on receiving brain regions, glands, and ducts.

Comparative study of the gular gland of three species of Molossidae bats (Mammalia: Chiroptera) from South America.

The gular gland is a skin gland located in the suprasternal region of adult males of some bat families. Knowledge of the morphology and functional aspects of these gland types is often limited. This study aimed to describe the structure and composition of the gular glands of three molossid species (Eumops patagonicus, Molossus fluminensis and Molossus molossus) with respect to their reproductive activity and to define the mechanism involved in secretion release. Different histological, histochemical and immunohistochemical techniques were used to achieve these goals. The results revealed that the size and composition of this gland are variable and are mostly related to the lipid content during the reproductive season. The results also documented, for the first time, the occurrence of mechanoreceptors associated with the surface of the glandular duct by detecting an S100 protein, indicating that an external stimulus activates secretion. Previous studies on other species have classified the gland using obsolete criteria; hence, we adopted a new classification of adenomeres in this study. Moreover, we investigated the gland secretion mechanism previously proposed. This study defines the implications of this gland in the reproduction of this species. Our preliminary interpretation of the function of the gular gland is that it is a cutaneous exocrine gland activated by mechanoreceptors involved in the reproductive behaviour of the Molossidae family.

Ontogeny of cranial musculoskeletal anatomy and its relationship to allometric increase in bite force in an insectivorous bat (Eptesicus fuscus).

Bite force is a performance metric commonly used to link cranial morphology with dietary ecology, as the strength of forces produced by the feeding apparatus largely constrains the foods an individual can consume. At a macroevolutionary scale, there is evidence that evolutionary changes in the anatomical elements involved in producing bite force have contributed to dietary diversification in mammals. Much less is known about how these elements change over postnatal ontogeny. Mammalian diets drastically shift over ontogeny-from drinking mother's milk to feeding on adult foods-presumably with equally drastic changes in the morphology of the feeding apparatus and bite performance. Here, we investigate ontogenetic morphological changes in the insectivorous big brown bat (Eptesicus fuscus), which has an extreme, positive allometric increase in bite force during development. Using contrast-enhanced micro-computed tomography scans of a developmental series from birth to adult morphology, we quantified skull shape and measured skeletal and muscular parameters directly related to bite force production. We found pronounced changes in the skull over ontogeny, including a large increase in the volume of the temporalis and masseter muscles, and an expansion of the skull dome and sagittal crest that would serve to increase the temporalis attachment area. These changes indicate that development of the jaw adductors play an important role in the development of biting performance of these bats. Notably, static bite force increases with positive allometry with respect to all anatomical measures examined, suggesting that modifications in biting dynamics and/or improved motor coordination also contribute to increases in biting performance.

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.

A neglected normal anatomical structure in mammal: a study in bats and tree shrews / Una estructura anatómica normal desatendida en mamíferos: un estudio en murciélagos y musarañas arborícolas

SUMMARY: The myodural bridge is a dense connective tissue connecting muscles and ligaments to the spinal dura mater in the atlanto-occipital interspace. Some researchers believe that the myodural bridge may play a vital physiological role. It is possible, for instance, that the prevention of spinal dura mater infoldings might be involved in regulated cerebrospinal fluid circulation. For instance, it is possible to prevent spinal dura mater infoldings, regulating cerebrospinal circulation. Bats are nocturnal and the only mammals that can perform a genuine and sustained flight, whereas tree shrews are arboreal mammals that often climb to a high altitude of about 10,000 feet. Both animals have lifestyles that are different from other previously studied mammals. The study of these two animals will shed further light on the existence of the myodural bridge in mammals. Gross anatomical dissection was used to observe the connections between the deep muscles of the neck and the dura mater at the level of the atlanto-occipital interspace. The existing structures were analyzed using conventional and special histological staining techniques. The suboccipital regions in bats and tree shrews contained the rectus capitis dorsal major (RCDma), rectus capitis dorsal minor (RCDmi), oblique capitis anterior (OCA), and oblique capitis posterior (OCP). Dense connective tissue connects the RCDmi to the posterior atlanto-occipital membrane (PAOM) and the latter to the spinal dura mater. The myodural bridge in these mammals shares a similar structure to the myodural bridge in humans. Histological analyses confirmed that the connective fibers of the myodural bridge were primarily type I collagen fibers. In this study, it is supplemented by the existence of the myodural bridge in mammals. This further demonstrates that myodural bridge widely exists in the normal anatomy of mammals. This provides morphological support for a comparative anatomical study of the physiological function of the myodural bridge.

El puente miodural es un tejido conjuntivo denso que conecta los músculos y los ligamentos a la duramadre espinal en el espacio atlanto-occipital. Algunos investigadores creen que el puente miodural puede desempeñar un papel fisiológico vital. Es posible, por ejemplo, que la prevención de los pliegues de la duramadre espinal pueda estar involucrada en la circulación regulada del líquido cefalorraquídeo. En esta instancia, es posible prevenir los pliegues de la duramadre espinal, regulando la circulación cerebro espinal. Los murciélagos son animales nocturnos y los únicos mamíferos que pueden realizar un vuelo real y sostenido, mientras que las musarañas arborícolas son mamíferos arbóreos que a menudo ascienden a una gran altura de unos 10 000 pies. Ambos animales tienen estilos de vida diferentes a los de otros mamíferos previamente estudiados. El estudio de estos dos animales ofrecerá más información sobre la existencia del puente miodural en los mamíferos. Se realizó una disección anatómica macroscópica para observar las conexiones entre los músculos profundos del cuello y la duramadre a nivel del espacio atlanto-occipital. Las estructuras existentes se analizaron mediante técnicas de tinción histológica convencionales y especiales. Las regiones suboccipitales en murciélagos y musarañas arbóreas presentaban el músculo recto dorsal mayor de la cabeza (RCDma), el recto dorsal menor de la cabeza (RCDmi), el oblicuo anterior de la cabeza (OCA) y el oblicuo posterior de la cabeza (OCP). El tejido conjuntivo denso conecta el RCDmi con la membrana atlanto- occipital posterior (PAOM) y esta última con la duramadre espinal. El puente miodural en estos mamíferos comparte una estructura similar al puente miodural en humanos. Los análisis histológicos confirmaron que las fibras conectivas del puente miodural son principalmente fibras de colágeno tipo I. Esto demuestra además que el puente miodural existe ampliamente en la anatomía normal de los mamíferos. Esta investigación proporciona apoyo morfológico para un estudio anatómico comparativo de la función fisiológica del puente miodural.

Morphological variation of the brachial plexus in four phyllostomid bat species (Chiroptera, Phyllostomidae).

Despite the remarkable morphological modifications that occurred in the thoracic limbs of bats, information about the brachial plexus in this group is still scarce. The present study aimed to describe the origin, structure, and distribution of these peripheral nerves in four Phyllostomidae species. Both antimeres of six Artibeus lituratus, five Desmodus rotundus, seven Glossophaga soricina, and five Phyllostomus hastatus-all adult males from the Adriano Lúcio Peracchi Collection (UFRRJ)-were dissected. After complete exposure of the structure, we found that the brachial plexus of D. rotundus and P. hastatus is formed by the same roots (C5-T1), whereas the fourth cervical spinal nerve and the second thoracic spinal nerve are present in G. soricina (C4-T1) and A. lituratus (C5-T2), respectively. There was intraspecific variation and asymmetry in the origin of the structure and the combinations of nerve segments forming terminal branches. The distribution to the target muscles and patagium, however, was not subject to significant variation in our sample. Data presented here support the presence of two prevailing conditions in distribution of nerves to the bat muscles, and the innervation of the membranes seems to be explained by embryogenesis. Although the brachial plexus in phyllostomid bats is similar to that of other terrestrial Laurasiatheria, aspects identified in these bats, apparently unique to Chiroptera, may be related to anatomical changes in the thoracic limbs functionally linked to flight.

Comparative analysis of male reproductive accessory glands in bats Histiotus velatus (Vespertilionidae), Molossus rufus (Molossidae), and Peropteryx leucoptera (Emballonuridae).

Despite the high number of species and wide geographic dispersion, reproductive accessory glands (RAGs) of bats have traditionally received little attention in the literature, with some species not even having a basic description of their composition and structure. Thus, this study aimed to analyze and compare the composition, anatomy, and histology of male RAGs of bat species belonging to three of the largest (cosmopolitan) bat families: Vespertilionidae (Histiotus velatus), Molossidae (Molossus rufus), and Emballonuridae (Peropteryx leucoptera), in order to understand the variations in the bat RAGs. The results showed that the RAGs of H. velatus, M. rufus, and P. leucoptera are composed of an intra-abdominal prostatic complex, associated with the urethra, urethral glands, and a pair of inguinal bulbourethral glands; without ampullary glands or seminal vesicles. The prostatic complex can be composed of two (M. rufus and P. leucoptera) or three (H. velatus) prostatic regions, and can be compact (P. leucoptera), semi-lobed (M. rufus), or multilobed (H. velatus). Each prostatic region has unique and distinct characteristics, with the ventral region presenting a holocrine nature, exclusive to bats; while the dorsal and/or dorsolateral regions have similar characteristics to the ventral prostate of rats and to the human peripheral zone.

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.

Molecular identification of genus Pipistrellus (Mammalia: Chiroptera) from Fata region, Pakistan / Identificação molecular do gênero Pipistrellus (Mammalia: Chiroptera) da região de Fáta, Paquistão

A total of 10 specimens were captured from selected sites of Bajaur Agency FATA, Pakistan using mist nets. The captured specimens were morphologically identified and various morphometric measurements were taken. The head and Body length (HB) of Pipistrellus coromondra and Pipistrellus kuhlii lepidus (n=10) was 43±0.11 mm and 45±1.1 respectively. Morphologically identified Pipistrellus kuhlii confirmed as Pipistrellus kuhlii lepidus based on 16S rRNA sequences. The DNA sequences were submitted to GenBank and accession numbers were obtained (MN719478 and MT430902). The available 16S rRNA gene sequences of Pipistrellus coromondra and Pipistrellus kuhlii lepidus were retrieved from NCBI and incorporated in N-J tree analysis. Overall, the interspecific genetic variations among Pipistrellus coromondra and Pipistrellus kuhlii lepidus were 8% and 1% respectively. In our recommendation, a comprehensive molecular identification of bats is need of hour to report more cryptic and new species from Pakistan.

Um total de 10 espécimes foi capturado em locais selecionados da Bajaur Agency FATA, Paquistão, usando redes de neblina. Os espécimes capturados foram identificados morfologicamente e várias medidas morfométricas foram realizadas. O comprimento da cabeça e do corpo (HB) de Pipistrellus coromondra e Pipistrellus kuhlii lepidus (n = 10) foi de 43 ± 0,11 mm e 45 ± 1,1, respectivamente. Pipistrellus kuhlii identificado morfologicamente e confirmado como Pipistrellus kuhlii lepidus com base em sequências de rRNA 16S. As sequências de DNA foram submetidas ao GenBank e os números de acesso foram obtidos (MN 719478 e MT430902). As sequências do gene 16S rRNA disponíveis de Pipistrellus coromondra e Pipistrellus kuhlii lepidus foram recuperadas do NCBI e incorporadas na análise da árvore N-J. No geral, as variações genéticas interespecíficas entre Pipistrellus coromondra e Pipistrellus kuhlii lepidus foram de 8% e 1%, respectivamente. Em nossa recomendação, uma identificação molecular abrangente de morcegos precisa de uma hora para relatar mais espécies crípticas e novas do Paquistão.

Skull Shape Variations in the Eidolon helvum (African Fruit Bat) Based on Geographical Location.

The shape and size of a skull provides insight into the age, breed and gender of the animal. Skull shape variations have been reported in different animals, with some theories linking these variations to evolution and/or migration. This study assessed the variations observed in the skull shape, size and gross morphometrics of two groups of the Eidolon helvum obtained from two geographical regions in Nigeria (south and north). All skulls were rostro-caudally elongated, having a dolichocephalic appearance. The skulls from the north had a distinct dome shape, with a more prominent zygomatic process, absence of a 'diastema' and an extra upper molar, while the southern skulls showed a more dorsally flattened skull and a less prominent zygomatic process. The shape of the sagittal crest was different in the two groups, while there was the presence of an accessory infraorbital foramen in some of the southern skulls. The southern skulls lacked the palatine foramen. The lacrimal foramen was observed to be more caudally placed in the southern skulls. Values for most linear measurements were higher in the northern skulls, although statistically significant difference was not present in all. The value for the neurocranial volume was considerably higher in the northern skulls (4.41 ± 0.28 mls) relative to the southern skulls (2.0 ± 0.27 mls). Statistically significant differences were not observed between males and females (within regions). Data obtained from this study may find application in evolution and migration studies, wildlife medicine and surgery and comparative and forensic anatomy.

Ecological constraints on highly evolvable olfactory receptor genes and morphology in neotropical bats.

Although evolvability of genes and traits may promote specialization during species diversification, how ecology subsequently restricts such variation remains unclear. Chemosensation requires animals to decipher a complex chemical background to locate fitness-related resources, and thus the underlying genomic architecture and morphology must cope with constant exposure to a changing odorant landscape; detecting adaptation amidst extensive chemosensory diversity is an open challenge. In phyllostomid bats, an ecologically diverse clade that evolved plant visiting from a presumed insectivorous ancestor, the evolution of novel food detection mechanisms is suggested to be a key innovation, as plant-visiting species rely strongly on olfaction, supplementarily using echolocation. If this is true, exceptional variation in underlying olfactory genes and phenotypes may have preceded dietary diversification. We compared olfactory receptor (OR) genes sequenced from olfactory epithelium transcriptomes and olfactory epithelium surface area of bats with differing diets. Surprisingly, although OR evolution rates were quite variable and generally high, they are largely independent of diet. Olfactory epithelial surface area, however, is relatively larger in plant-visiting bats and there is an inverse relationship between OR evolution rates and surface area. Relatively larger surface areas suggest greater reliance on olfactory detection and stronger constraint on maintaining an already diverse OR repertoire. Instead of the typical case in which specialization and elaboration are coupled with rapid diversification of associated genes, here the relevant genes are already evolving so quickly that increased reliance on smell has led to stabilizing selection, presumably to maintain the ability to consistently discriminate among specific odorants-a potential ecological constraint on sensory evolution.

Counteracting forces of introgressive hybridization and interspecific competition shape the morphological traits of cryptic Iberian Eptesicus bats.

Cryptic species that coexist in sympatry are likely to simultaneously experience strong competition and hybridization. The first phenomenon would lead to character displacement, whereas the second can potentially promote morphological similarity through adaptive introgression. The main goal of this work was to investigate the effect of introgressive hybridization on the morphology of cryptic Iberian Eptesicus bats when facing counteracting evolutionary forces from interspecific competition. We found substantial overlap both in dentition and in wing morphology traits, though mainly in individuals in sympatry. The presence of hybrids contributes to a fifth of this overlap, with hybrids showing traits with intermediate morphometry. Thus, introgressive hybridization may contribute to species adaptation to trophic and ecological space responding directly to the macro-habitats characteristics of the sympatric zone and to local prey availability. On the other hand, fur shade tended to be browner and brighter in hybrids than parental species. Colour differences could result from partitioning of resources as an adaptation to environmental factors such as roost and microhabitats. We argue that a balance between adaptive introgression and niche partitioning shapes species interactions with the environment through affecting morphological traits under selection.

Facial muscle modification associated with chiropteran noseleaf development: Insights into the developmental basis of a movable rostral appendage in mammals.

BACKGROUND: Mammal evolution has generated diverse craniofacial morphologies, including remarkable movable rostral appendages. However, the muscular and skeletal architecture providing the mobility of these appendages remains largely unexplored. Here, we focus on chiropteran noseleaves and compare the three-dimensional internal morphology of late-stage embryos between the greater horseshoe bat Rhinolophus ferrumequinum, which possesses a noseleaf, and the Asian bent-winged bat Miniopterus fuliginosus and Egyptian fruit bat Rousettus aegyptiacus, which do not. We also assess earlier stage cell proliferation within the rostrum to elucidate cellular mechanisms underlying noseleaf-associated morphological modifications. RESULTS: The musculus maxillolabialis inserted into proximal vibrissae follicles in M fuliginosus and R aegyptiacus embryos but instead inserted into the horseshoe plate in R ferrumequinum. This modification suggests that the M maxillolabialis has adapted to controlling the noseleaf rather than vibrissae in rhinolophid bats. Our cellular analysis showed higher cell proliferation within the maxillary and frontonasal processes of St. 14 embryos in R ferrumequinum compared to M fuliginosus and R aegyptiacus, suggesting that the spatial alteration of noseleaf-associated muscle is derived from changes in facial morphogenesis that occur by St. 14. CONCLUSION: This is the first study clarifying the morphological and cellular bases underlying the development of mammalian rostral appendages.

Physical constraints on thermoregulation and flight drive morphological evolution in bats.

Body size and shape fundamentally determine organismal energy requirements by modulating heat and mass exchange with the environment and the costs of locomotion, thermoregulation, and maintenance. Ecologists have long used the physical linkage between morphology and energy balance to explain why the body size and shape of many organisms vary across climatic gradients, e.g., why larger endotherms are more common in colder regions. However, few modeling exercises have aimed at investigating this link from first principles. Body size evolution in bats contrasts with the patterns observed in other endotherms, probably because physical constraints on flight limit morphological adaptations. Here, we develop a biophysical model based on heat transfer and aerodynamic principles to investigate energy constraints on morphological evolution in bats. Our biophysical model predicts that the energy costs of thermoregulation and flight, respectively, impose upper and lower limits on the relationship of wing surface area to body mass (S-MR), giving rise to an optimal S-MR at which both energy costs are minimized. A comparative analysis of 278 species of bats supports the model's prediction that S-MR evolves toward an optimal shape and that the strength of selection is higher among species experiencing greater energy demands for thermoregulation in cold climates. Our study suggests that energy costs modulate the mode of morphological evolution in bats­hence shedding light on a long-standing debate over bats' conformity to ecogeographical patterns observed in other mammals­and offers a procedure for investigating complex macroecological patterns from first principles.

Evolution of inner ear neuroanatomy of bats and implications for echolocation.

Phylogenomics of bats suggests that their echolocation either evolved separately in the bat suborders Yinpterochiroptera and Yangochiroptera, or had a single origin in bat ancestors and was later lost in some yinpterochiropterans1-6. Hearing for echolocation behaviour depends on the inner ear, of which the spiral ganglion is an essential structure. Here we report the observation of highly derived structures of the spiral ganglion in yangochiropteran bats: a trans-otic ganglion with a wall-less Rosenthal's canal. This neuroanatomical arrangement permits a larger ganglion with more neurons, higher innervation density of neurons and denser clustering of cochlear nerve fascicles7-13. This differs from the plesiomorphic neuroanatomy of Yinpterochiroptera and non-chiropteran mammals. The osteological correlates of these derived ganglion features can now be traced into bat phylogeny, providing direct evidence of how Yangochiroptera differentiated from Yinpterochiroptera in spiral ganglion neuroanatomy. These features are highly variable across major clades and between species of Yangochiroptera, and in morphospace, exhibit much greater disparity in Yangochiroptera than Yinpterochiroptera. These highly variable ganglion features may be a neuroanatomical evolutionary driver for their diverse echolocating strategies4,14-17 and are associated with the explosive diversification of yangochiropterans, which include most bat families, genera and species.

The hyoid as a sound conducting apparatus in laryngeally echolocating bats.

The morphology of the stylohyal-tympanic bone articulation found in laryngeally echolocating bats is highly indicative of a function associated with signal production. One untested hypothesis is that this morphology allows the transfer of a sound signal from the larynx to the tympanic bones (auditory bulla) via the hyoid apparatus during signal production by the larynx. We used µCT data and finite element analysis to model the propagation of sound through the hyoid chain into the tympanic bones to test this hypothesis. We modeled sound pressure (dB) wave propagation from the basihyal to the tympanic bones, vibratory behavior (m) of the stylohyal-tympanic bone unit, and the stylohyal and tympanic bones when the stylohyal bone is allowed to pivot on the tympanic bone. Sound pressure wave propagation was modeled using the harmonic acoustics solver in ANSYS and vibratory behavior was modeled using coupled modal and harmonic response analyses in ANSYS. For both analyses (harmonic acoustics and harmonic response), the input excitation on the basihyal and thyrohyals was modeled as the estimated pressure (Pa) imposed by the collision of the vibrating thyroid cartilage of the larynx against these bones during signal production. Our models support the hypothesis that this stereotypical hyoid morphology found in laryngeally echolocating bats can transfer sound to the auditory bullae at an amplitude that is likely heard for the species Artibeus jamaicensis and Rhinolophus pusillus.

Venous networks in the upper airways of bats: A histological and diceCT study.

Our knowledge of nasal cavity anatomy has grown considerably with the advent of micro-computed tomography (CT). More recently, a technique called diffusible iodine-based contrast-enhanced CT (diceCT) has rendered it possible to study nasal soft tissues. Using diceCT and histology, we aim to (a) explore the utility of these techniques for inferring the presence of venous sinuses that typify respiratory mucosa and (b) inquire whether distribution of vascular mucosa may relate to specialization for derived functions of the nasal cavity (i.e., nasal-emission of echolocation sounds) in bats. Matching histology and diceCT data indicate that diceCT can detect venous sinuses as either darkened, "empty" spaces, or radio-opaque islands when blood cells are present. Thus, we show that diceCT provides reliable information on vascular distribution in the mucosa of the nasal airways. Among the bats studied, a nonecholocating pteropodid (Cynopterus sphinx) and an oral-emitter of echolocation sounds (Eptesicus fuscus) possess venous sinus networks that drain into the sphenopalatine vein rostral to the nasopharynx. In contrast, nasopharyngeal passageways of nasal-emitting hipposiderids are notably packed with venous sinuses. The mucosae of the nasopharyngeal passageways are far less vascular in nasal-emitting phyllostomids, in which vascular mucosae are more widely distributed in the nasal cavity, and in some nectar-feeding species, a particularly large venous sinus is adjacent to the vomeronasal organ. Therefore, we do not find a common pattern of venous sinus distribution associated with nasal emission of sounds in phyllostomids and hipposiderids. Instead, vascular mucosa is more likely critical for air-conditioning and sometimes vomeronasal function in all bats.