Physics of directional hearing in the cricket Gryllus bimaculatus

In the cricket ear, sound acts on the external surface of the tympanum and also reaches the inner surface after travelling in at least three pathways in the tracheal system. We have determined the transmission gain of the three internal sound pathways; that is, the change of amplitude and phase angle from the entrances of the tracheal system to the inner surface of the tympanum. In addition, we have measured the diffraction and time of arrival of sound at the ear and at the three entrances at various directions of sound incidence. By combining these data we have calculated how the total driving force at the tympanum depends on the direction of sound. The results are in reasonable agreement with the directionality of the tympanal vibrations as determined with laser vibrometry.At the frequency of the calling song (4.7 kHz), the direction of the sound has little effect on the amplitudes of the sounds acting on the tympanum, but large effects on their phase angles, especially of the sound waves entering the tracheal system at the contralateral side of the body. The master parameter for causing the directionality of the ear in the forward direction is the sound wave entering the contralateral thoracic spiracle. The phase of this sound component may change by 130–140° with sound direction. The transmission of sound from the contralateral inputs is dominated by a very selective high-pass filter, and large changes in amplitude and phase are seen in the transmitted sounds when the sound frequency changes from 4 to 5 kHz. The directionality is therefore very dependent on sound frequency.The transmission gains vary considerably in different individuals, and much variation was also found in the directional patterns of the ears, especially in the effects of sounds from contralateral directions. However, the directional pattern in the frontal direction is quite robust (at least 5 dB difference between the 330° and 30° directions), so these variations have only little effect on how well the individual animals can approach singing conspecifics.Abbreviations CS contralateral spiracle - CT contralateral tympanum - IS ipsilateral spiracle - IT ipsilateral tympanum - P the vectorial sum of the sounds acting on the tympanum     

Convergence vs. Specialization in the ear region of moles (mammalia)

We investigated if and how the inner ear region undergoes similar adaptations in small, fossorial, insectivoran‐grade mammals, and found a variety of inner ear phenotypes. In our sample, afrotherian moles (Chrysochloridae) and the marsupial Notoryctes differ from most other burrowing mammals in their relatively short radii of semicircular canal curvature; chrysochlorids and fossorial talpids share a relatively long interampullar width. Chrysochlorids are unique in showing a highly coiled cochlea with nearly four turns. Extensive cochlear coiling may reflect their greater ecological dependence on low frequency auditory cues compared to talpids, tenrecids, and the marsupial Notoryctes. Correspondingly, the lack of such extensive coiling in the inner ear of other fossorial species may indicate a greater reliance on other senses to enable their fossorial lifestyle, such as tactile sensation from vibrissae and Eimer's organs. The reliance of chrysochlorids on sound is evident in the high degree of coiling and in the diversity of its mallear types, and may help explain the lack of any semiaquatic members of that group. The simplest mallear types among chrysochlorids are not present in the basal‐most members of that clade, but all extant chrysochlorids investigated to date exhibit extensive cochlear coiling. The chrysochlorid ear region thus exhibits mosaic evolution; our data suggest that extensive coiling evolved in chrysochlorids prior to and independently of diversification in middle ear ossicle size and shape. J. Morphol. 276:900–914, 2015. © 2015 Wiley Periodicals, Inc.     

Diversity and Evolution of the Marsupial Mandibular Angular Process

A medial inflection of the mandibular angular process is present in most marsupials. The few living marsupials that lack this trait either are very specialized forms (e.g., Tarsipes) or show a medial inflection at some point in development that is lost in later ontogenetic stages (cf. Dactylopsila and Phascolarctos). A medially inflected angular process is not present in any known extant or extinct placental (including all Cretaceous taxa that preserve the back of the dentary bone). Some extant placentals with enlarged auditory bullae evolved a medial flange of the angular process as a strategy to increase gape, but this is not homologous to the marsupial condition. We conclude that the medially inflected angular process is a shared derived trait of extant and extinct marsupials. The significant diversity in the form of the medially inflected mandibular angular process in marsupials, documented here for 53 taxa, shows a general relation to dietary adaptations. Herbivores (with well-developed masseter and medial pterygoid muscles) tend to have a shelf-like angular process, while small, insectivorous marsupials generally have a rod-like angular process. A close connection between the angular process and the ectotympanic is maintained during early postnatal development in all marsupials examined, a relation not seen in the placentals examined. A previous hypothesis suggested that the angular process plays a role in hearing in pouch-young Monodelphis. Data on the maturation of the auditory system does not support this hypothesis. Currently there are no data on differences in muscular anatomy or mastication between marsupials and placentals that could serve as a causal explanation for the difference in adult form of the angular process between the two groups.     

Bone‐conduction hearing and seismic sensitivity of the late permian anomodont Kawingasaurus fossilis

An investigation of the internal cranial anatomy of the anomodont Kawingasaurus from the Upper Permian Usili Formation in Tanzania by means of neutron tomography revealed an unusual inner and middle ear anatomy such as extraordinarily inflated vestibules, lateroventrally orientated stapes with large footplates, and a small angle between the planes of the anterior and lateral semicircular canals. The vestibule has a volume, which is about 25 times larger than the human vestibule, although Kawingasaurus has only a skull length of approximately 40 mm. Vestibule inflation and enlarged stapes footplates are thought to be functionally correlated with bone‐conduction hearing; both morphologies have been observed in fossorial vertebrates using seismic signals for communication. The firmly fused triangular head with spatulate snout was probably used for digging and preadapted to seismic signal detection. The quadrate‐quadratojugal complex was able to transmit sound from the articular to the stapes by small vibrations of the quadrate process, which formed a ball and socket joint with the squamosal. Mechanical considerations suggest that the ventrolaterally orientated stapes of Kawingasaurus was mechanically better suited to transmit seismic sound from the ground to the fenestra vestibuli than a horizontal orientated stapes. The low sound pressure level transformer ratio of 2–3 in Kawingasaurus points to a seismic sensitivity of the middle ear and a vestigial or reduced sensitivity to airborne sound. Three hypothetical pathways of bone conduction in Kawingasaurus are discussed: 1) sound transmission via the spatulate snout and skull roof to the otic capsules, 2) relative movements resulting from the inertia of the mandible if sound is percepted with the skull, and 3) bone conduction from the substrate via mandible, jaw articulation, and stapes to the inner ear. J. Morphol. 276:121–143, 2015. © 2014 Wiley Periodicals, Inc.     

How to build a mammalian super-predator

Questions surrounding the biology of large fossil predators that differ markedly from living forms have long intrigued palaeobiologists. Among such taxa few have excited more interest than sabertooth cats, whose distinctive hypertrophied canines are suggestive of killing behaviors and feeding ecologies that may have departed widely from those of extant carnivores. Moreover, considerable variation among sabertooth species is further suggestive of intriguing differences within the group. Behavior and ecology in another large, extinct mammalian carnivore, the Australian marsupial lion (Thylacoleo carnifex), has also proven contentious. In this study, we assemble a wide range of cranio-dental and postcranial indices in a dataset including machairodont sabertooths, T. carnifex and an extensive sample of extant taxa in order to examine the palaeobiology of these charismatic fossil carnivores. Results of multivariate analyses point to significant relationships between behavior and overall body proportions in extant mammalian carnivores. Postcranial morphologies of two American dirk-tooth species of sabertooth (Smilodon) depart greatly from those of living felids and group most closely with bears among living placentals. Scimitar-tooth species of Homotherium and Machairodus cluster with modern pantherine cats. The marsupial lion groups with Smilodon. If these latter two phylogenetically disparate clades do represent a specialized, robust ecomorph adapted to predation on large prey, then it is a body plan that might be effectively identified on the basis of a handful of ‘bear-like’ postcranial features in combination with a more typically ‘felid-like’ carnassialization of the cheektooth row.     

Sparassocynus (Marsupialia, Didelphidae), a peculiar mammal from the late Cenozoic of Argentina

The extinct genus Sparassocynus is known from the Montehermosan, Chapadmalalan, and Uquian stages of Argentina, spanning the Pliocene-Pleistocene transition, and a relative occurs in the older Huayquerian. After a taxonomict review, the morphology of skull, mandible, and dentition is described. The short, triangular face, wide zygomata, broad cranium with large completely bone-enclosed hypo- and epitympanic sinuses, and carnassialized molars are unique among known American marsupials. All these characters are functionally convergent toward living Australian phascogaline dasyurids, small marsupial carnivores, although phylogenetically Sparassocynus clearly represents a moderately specialized offshoot of the American family Didelphidae. It represents a small steppe carnivore now ecologically replaced, at least in part, by placental carnivores that spread from North America in the late Pliocene and Pleistocene.     

Changes in the mechanics of the cricket ear during the early days of adult life

From behavioural experiments it is known that the thresholds for both positive and the negative phonotaxis in crickets (Gryllus bimaculatus) decrease during the first days of adult life. Neuronal recordings have shown that a part of the changes in threshold has its origin in the ears. In this study we investigate some changes of the mechanics of the ears in the days after the imaginal moult.The posterior tympanum starts to work as an acoustic window only after the imaginal moult. During the first days the vibration amplitude tends to increase, except below 4 kHz and between 6 and 12 kHz. In the mature hearing organ, the tympanal vibrations exceed those of the surrounding cuticle up to ca. 50 kHz, and peaks of vibration amplitude are found around 5 and 15 kHz (the frequencies of the calling and courtship songs). The appearance of these peaks is caused, at least in part, by a change in the mechanics of the tympanum.Sound propagation through the trachea connecting the ipsilateral acoustic spiracle and the inner surface of the tympanum does not change much during the first week of adult life. In contrast, the propagation from the contralateral spiracle improves considerably. Thus the tympanum of the newly moulted cricket receives only little sound from the contralateral spiracle, and therefore the ear lacks the sound component which is essential for directional hearing in the mature cricket.     

Spatial hearing in Cope’s gray treefrog: II. Frequency-dependent directionality in the amplitude and phase of tympanum vibrations

Anuran ears function as pressure difference receivers, and the amplitude and phase of tympanum vibrations are inherently directional, varying with sound incident angle. We quantified the nature of this directionality for Cope’s gray treefrog, Hyla chrysoscelis. We presented subjects with pure tones, advertisement calls, and frequency-modulated sweeps to examine the influence of frequency, signal level, lung inflation, and sex on ear directionality. Interaural differences in the amplitude of tympanum vibrations were 1–4 dB greater than sound pressure differences adjacent to the two tympana, while interaural differences in the phase of tympanum vibration were similar to or smaller than those in sound phase. Directionality in the amplitude and phase of tympanum vibration were highly dependent on sound frequency, and directionality in amplitude varied slightly with signal level. Directionality in the amplitude and phase of tone- and call-evoked responses did not differ between sexes. Lung inflation strongly affected tympanum directionality over a narrow frequency range that, in females, included call frequencies. This study provides a foundation for further work on the biomechanics and neural mechanisms of spatial hearing in H. chrysoscelis, and lends valuable perspective to behavioral studies on the use of spatial information by this species and other frogs.     

The Auditory Mechanics of the Outer Ear of the Bush Cricket: A Numerical Approach

Bush crickets have tympanal ears located in the forelegs. Their ears are elaborate, as they have outer-, middle-, and inner-ear components. The outer ear comprises an air-filled tube derived from the respiratory trachea, the acoustic trachea (AT), which transfers sound from the mesothoracic acoustic spiracle to the internal side of the ear drums in the legs. A key feature of the AT is its capacity to reduce the velocity of sound propagation and alter the acoustic driving forces of the tympanum (the ear drum), producing differences in sound pressure and time between the left and right sides, therefore aiding the directional hearing of the animal. It has been demonstrated experimentally that the tracheal sound transmission generates a gain of ∼15 dB and a propagation velocity of 255 ms⁻¹, an approximately 25% reduction from free-field propagation. However, the mechanism responsible for this change in sound pressure level and velocity remains elusive. In this study, we investigate the mechanical processes behind the sound pressure gain in the AT by numerically modeling the tracheal acoustic behavior using the finite-element method and real three-dimensional geometries of the tracheae of the bush cricket Copiphora gorgonensis. Taking into account the thermoviscous acoustic-shell interaction on the propagation of sound, we analyze the effects of the horn-shaped domain, material properties of the tracheal wall, and the thermal processes on the change in sound pressure level in the AT. Through the numerical results obtained, it is discerned that the tracheal geometry is the main factor contributing to the observed pressure gain.     

Fossil evidence of evolutionary convergence in juvenile dental morphology and upper canine replacement in sabertooth carnivores

The convergent suite of morphological traits characterizing the mammalian sabertooth ecomorphology is well documented, including modifications of the dental and osteological portions of the masticatory apparatus from a less‐specialized carnivore condition. Equally important is how those specialized adult morphologies developed through ontogeny because previous studies have shown that growing such specialized craniodental traits may require evolutionary modification of growth patterns and tooth replacement mechanisms. Despite the understanding of convergent morphological specialization in adult sabertooth carnivores, the possibility of a convergent ontogenetic trajectory toward those adult morphologies has not been rigorously examined. The present study examines numerous previously undescribed juvenile nimravid specimens. The results provide insights about nimravid ontogeny and show, for the first time, that the nimravid sabertooth lineage included species in which the permanent upper canine erupted within a lingual concavity of the deciduous upper canine until it reached comparable crown height beyond the alveolar border. Furthermore, this investigation assesses the juvenile morphology and upper canine replacement of felid and barbourofelid sabertooth taxa. The results provide evidence of convergence in deciduous upper canine morphology of three sabertooth carnivore lineages (i.e., nimravid, felid, and barbourofelid), as well as preliminary evidence of convergence in the upper canine replacement process. It might be beneficial for studies of extreme morphological specialization to simultaneously consider convergence in adult morphologies and how morphologies change through ontogeny.     

Scaling of the marsupial middle ear and its functional significance

The marsupial middle ear performs an anatomical impedance matching for acoustic energy travelling in air to reach the cochlea. The size of the middle ear sets constraints for the frequencies transmitted. For generalized placental mammals, it has been shown that the limit for high-frequency hearing can be predicted on the basis of middle ear ossicle mass, provided that the ears fulfil requirements of isometry. We studied the interspecific size variation of the middle ear in 23 marsupial species, with the following measurable parameters: skull mass, condylobasal length, ossicular masses for malleus, incus and stapes, tympanic membrane area, oval window area, and lever arm lengths for malleus and incus. Our results show that the middle ear size grows with negative allometry in relation to body size and that the internal proportions of the marsupial middle ear are largely isometric. This resembles the situation in placental mammals and allows us to use their isometric middle ear model to predict the high-frequency hearing limit for marsupials. We found that the isometry model predicts the high-frequency hearing limit for different marsupials well, indicating that marsupials can be used as auditory models for general therian mammalian hearing. At very high frequencies, other factors, such as the inner ear, seem to constrain mammalian hearing.     

Evolutionary convergence of primitive sabertooth craniomandibular morphology: the clouded leopard (<Emphasis Type="Italic">Neofelis nebulosa</Emphasis>) and <Emphasis Type="Italic">Paramachairodus ogygia</Emphasis> compared

The sabertoothed felids were among the most unusual predators in the late Tertiary ecosystems, and the sabertooth morphology is regarded as being absent from the modern ecosystems. In recent years, the primitive Paramachairodus has become well known and has yielded much valuable information on the primitive skull morphology among sabercats, providing the first evidence-based scenarios for the evolution of skull morphology in later sabercats. However, comparison of craniomandibular morphology of the extant clouded leopard Neofelis nebulosa and Paramachairodus reveals numerous similarities and subsequent divergence from other extant great cats. In several key aspects, the clouded leopard has approached a primitive sabercat craniomandibular morphology and has diverged markedly from its sister group, the Panthera lineage. A primitive sabertooth condition arose six times in the Tertiary period, not five as is traditionally advocated. The clouded leopard appears to be a useful model for understanding primitive sabercat morphology and could shed important light on sabercat evolution. The unusual nature of the clouded leopard implies that increased efforts should be spent on insuring the continuing survival of this rare and endangered species. Electronic Supplementary Material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Azimuthal sound localization in the European starling (Sturnus vulgaris)

Summary The physical measurements reported here test whether the European starling (Sturnus vulgaris) evaluates the azimuth direction of a sound source with a peripheral auditory system composed of two acoustically coupled pressure-difference receivers (1) or of two decoupled pressure receivers (2).A directional pattern of sound intensity in the freefield was measured at the entrance of the auditory meatus using a probe microphone, and at the tympanum using laser vibrometry. The maximum differences in the soundpressure level measured with the microphone between various speaker positions and the frontal speaker position were 2.4 dB at 1 and 2 kHz, 7.3 dB at 4 kHz, 9.2 dB at 6 kHz, and 10.9 dB at 8 kHz. The directional amplitude pattern measured by laser vibrometry did not differ from that measured with the microphone. Neither did the directional pattern of travel times to the ear. Measurements of the amplitude and phase transfer function of the starling's interaural pathway using a closed sound system were in accord with the results of the free-field measurements.In conclusion, although some sound transmission via the interaural canal occurred, the present experiments support the hypothesis 2 above that the starling's peripheral auditory system is best described as consisting of two functionally decoupled pressure receivers.Abbreviations CM cochlear microphonics - ITD interaural time difference - IID interaural intensity difference - MRA minimum resolvable angle - dB SPL sound-pressure level (re 0.00002 Pa)     

Do Australian small mammals respond to native and introduced predator odours?

Abstract Coevolution is thought to have led to many small mammal species avoiding the scent marks of their main mammalian predators, as they provide a reliable cue to predation risk. Most support for this hypothesis comes from northern hemisphere predator/prey systems, however, it is unclear whether this avoidance of predator faecal odour occurs in Australia's mammalian fauna, which has evolved in relative isolation from the rest of the world, and is dominated by marsupials rather than placentals. We tested this theory for an Australian system with marsupial and placental predators and prey, that share a long‐term (>1 million years) or short‐term (<150 years) exposure to each other. The predators were the native marsupial tiger quoll Dasyurus maculatus and the introduced placental red fox Vulpes vulpes. The potential prey were three native rodent species, the bush rat Rattus fuscipes, the swamp rat Rattus lutreolus, the eastern chestnut mouse Pseudomys gracilicaudatus, and the marsupial brown antechinus Antechinus stuartii. Small mammals were captured in Elliott traps with 1/3 of traps treated with fox faeces, 1/3 treated with quoll faeces and the remainder left untreated. The native rodent species all showed avoidance of both tiger quoll and red fox odours whereas the marsupial antechinus showed no responses to either odour. Either predator odour avoidance has not evolved in this marsupial or their reaction to predator odours may be exhibited in ways which are not recognizable through trapping. The avoidance by the rodents of fox odour as well as quoll odour indicates this response may either be due to common components in fox and quoll odour, or it may be a recently evolved response.     

The petrosal and inner ear of the Late Jurassic cladotherian mammal Dryolestes leiriensis and implications for ear evolution in therian mammals

Dryolestes leiriensis is a Late Jurassic fossil mammal of the dryolestoid superfamily in the cladotherian clade that includes the extant marsupials and placentals. We used high resolution micro‐computed tomography (µCT) scanning and digital reconstruction of the virtual endocast of the inner ear to show that its cochlear canal is coiled through 270°, and has a cribriform plate with the spiral cochlear nerve foramina between the internal acoustic meatus and the cochlear bony labyrinth. The cochlear canal has the primary bony lamina for the basilar membrane with a partially formed (or partially preserved) canal for the cochlear spiral ganglion. These structures, in their fully developed condition, form the modiolus (the bony spiral structure) of the fully coiled cochlea in extant marsupial and placental mammals. The CT data show that the secondary bony lamina is present, although less developed than in another dryolestoid Henkelotherium and in the prototribosphenidan Vincelestes. The presence of the primary bony lamina with spiral ganglion canal suggests a dense and finely distributed cochlear nerve innervation of the hair cells for improved resolution of sound frequencies. The primary, and very probably also the secondary, bony laminae are correlated with a more rigid support for the basilar membrane and a narrower width of this membrane, both of which are key soft‐tissue characteristics for more sensitive hearing for higher frequency sound. All these cochlear features originated prior to the full coiling of the therian mammal cochlea beyond one full turn, suggesting that the adaptation to hearing a wider range of sound frequencies, especially higher frequencies with refined resolution, has an ancient evolutionary origin no later than the Late Jurassic in therian evolution. The petrosal of Dryolestes has added several features that are not preserved in the petrosal of Henkelotherium. The petrosal characters of dryolestoid mammals are essentially the same as those of Vincelestes, helping to corroborate the synapomorphies of the cladotherian clade in neural, vascular, and other petrosal characteristics. The petrosal characteristics of Dryolestes and Henkelotherium together represent the ancestral morphotype of the cladotherian clade (Dryolestoidea + Vincelestes + extant Theria) from which the extant therian mammals evolved their ear region characteristics. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166 , 433–463.     

The Opossum genome reveals further evidence for regulatory evolution in mammalian diversification

The sequencing of the euchromatic genome of a marsupial, the opossum Monodelphis domestica, identifies shared and unique features of marsupial and placental genomes and reveals a prominent role for the evolution of non-protein-coding elements.     

Locomotor correlates of the scapholunar of living and extinct carnivorans

The relationship of carpal morphology to ecology and habitat is under studied in carnivorans and more generally in mammals. Here, we use 3D-scanning techniques to assess the usefulness of a carpal bone, the scapholunar, in carnivorans to reflect ecology and habitat, and to reconstruct the ecology of five extinct carnivorans from two fossil sites: Rancho La Brea and Natural Trap Cave. We 3D-scanned scapholunars and measured articular surface areas and angles between articular facets using GeoMagic and Rhino 3D-software. We analyzed the difference in these metrics using multivariate analysis of variance and discriminant function analysis. Results show that the scapholunar reflects ecological signal, with clear groupings of cursorial carnivorans and grappling/climbing carnivorans; however, phylogenetic signal was also present in the results with hyaenids, canids, and large felids in distinct morphospaces. Extinct species Miracinonyx trumani (American cheetah) and Smilodon fatalis (sabertooth cat) showed surprising results with M. trumani grouping with pantherines instead of Acinonyx or Puma, suggesting it runs but still retains the ability to grapple prey. S. fatalis groups with pantherines, but also shows some unique adaptations, suggesting it had a different range of wrist motion than living cats. Overall, the scapholunar is a good indicator of ecology and functional morphology and can be another tool to use in modern and fossil carnivorans to reconstruct extinct ecologies and locomotor behaviors.     

改良乳突根治术联合后上壁重建对上鼓室胆脂瘤型中耳炎患者听力改善及复发率的影响

摘要 目的：探讨改良乳突根治术联合后上壁重建对上鼓室胆脂瘤型中耳炎患者听力改善及复发率的影响。方法：选取本院2015年5月-2020年10月收治的62例上鼓室胆脂瘤型中耳炎患者作为研究对象,随机将其分为改良组（n=31）和对照组（n=31）。改良组采用改良乳突根治术联合后上壁重建进行治疗,对照组采用乳突根治术进行治疗,对比两组患者手术前后听力情况、术后干耳所需时间等指标。结果：治疗前两组患者的气骨导差、气导听阀对比无明显差异（P>0.05）,治疗后均降低,并且改良组低于对照组（P＜0.05）;改良组患者术后并发症发生率较对照组低（P＜0.05）;改良组患者的术后2周、4周、8周干耳率较对照组高（P＜0.05）,术后干耳所需时间低于对照组（P＜0.05）;改良组治疗总有效率较对照组高（P＜0.05）。结论：将改良乳突根治术联合后上壁重建应用于上鼓室胆脂瘤型中耳炎患者当中,可提高患者听力,降低并发症,还可提高患者干耳率,缩短干耳时间,降低复发率,提高临床疗效,本研究值得临床借鉴。     

Evolution of the tetrapod ear: an analysis and reinterpretation

The dominant view of tetrapod otic evolution–the “standard view”–holds that the tympanum developed very early in tetrapod history and is homologous in all tetrapods and that the opercular process of the rhipidistian hyomandibula is homologous to the tympanic process of the stapes in lower tetrapods. Under that view, the labyrinthodont amphibians of the Paleozoic are usually considered ancestral to reptiles, and thus the “otic notch” of labyrinthodonts and the tympanum it presumably contained form the starting-point for middle ear evolution in reptiles. Four problems have classically been identified with the standard view: the differing relationships of the internal mandibular branch of N. VII (chorda tympani) to the processes of the stapes in amniotes and anurans; the differing orientations of the stapes in key fossil and living groups; the location of the tympanum in early fossil reptiles; and the transferral of the tympanum, during the origin of mammals, from the stapes to the articular bone of the lower jaw. An examination of these problems and of the solutions proposed under the standard view reveals the ad hoc, and therefore unsatisfactory, nature of the proposed solutions. To organize and review alternative hypotheses of otic evolution an analytical table is constructed, using three characters (tympanic process, Nerve VII, tympanum), each with two possible states. A total of eight hypotheses about middle ear evolution are possible under this system, one of which is the standard view. The seven “non-standard” hypotheses, only five of which have been argued in the literature, are briefly examined. Six of the “non-standard” hypotheses appear unattractive for various reasons, including reliance on ad hoc arguments. The seventh was first proposed by Gaupp in 1898. It is today almost universally ignored but apparently largely for historical rather than scientific reasons. This hypothesis, her called the “alternative view”, appears to rest on assumptions equally as plausible as those of the standard view. Moreover, it offers a solution of the problems associated with the standard view without, apparently, raising any similarly serious problems. This paper compares the standard and alternative views of middle ear evolution in detail. Comparison proceeds on two levels. On one level, they are compared in terms of the hypotheses of phyletic tetrapod relationships each promotes and how strongly each supports its hypothesis. Both views promote the same hypothesis of tetrapod relationships. The alternative view is the more parsimonious, but the difference is not considered sufficient to provide a choice. On another level, the two views are compared in terms of their implications for: (1) the evolution of relative and absolute auditory perceptive ability; (2) the origin of reptiles; (3) the evolution of the suspensorium and cranial kinesis; and (4) the origin and evolution of recent amphibians. The nature of the data required for a test of the implications of the two views is specified in each case. Where data are available. the alternative view is consistent and the standard view is inconsistent with these data. We conclude that the alternative view is the preferable hypothesis of middle-ear evolution. This conclusion implies the following: the tympanic membranes and the tympanic processes of the stapes in recent mammals, reptiles + birds. and frogs. are not homologous; the evolution of “special periotic systems” in the ancestors of amphibians and amniotes were independent events and preceded the evolution of tympanic membranes; the amphibian tympanic membrane. probably including that of labyrinthodonts. is not ancestral to that of amniotes. and that labyiinthodonts with an otic notch are not suitable as amniote ancestors; the stapes of early reptiles functioned primarily as part of the jaw suspension rather than in hearing; the mechanisms and abilities of sound perception in recent tetrapods are likely to be diverse rather than forming parts of a cline; and the lack of a tympanum in Gymnophiona and Caudata may be a retention of a primitive condition.     

Exceptionally high conservation of the MHC class I-related gene, MR1, among mammals

The major histocompatibility complex (MHC) class I-related gene, MR1, is a non-classical MHC class IA gene and is encoded outside the MHC region. The MR1 is responsible for activation of mucosal-associated invariant T (MAIT) cells expressing semi-invariant T cell receptors in the presence of bacteria, but its ligand has not been identified. A unique characteristic of MR1 is its high evolutionary conservation of the α1 and α2 domains corresponding to the peptide-binding domains of classical MHC class I molecules, showing about 90 % amino acid identity between human and mouse. To clarify the evolutionary history of MR1 and identify more critically conserved residues for the function of MR1, we searched for the MR1 gene using jawed vertebrate genome databases and isolated the MR1 cDNA sequences of marsupials (opossum and wallaby). A comparative genomic analysis indicated that MR1 is only present in placental and marsupial mammals and that the gene organization around MR1 is well conserved among analyzed jawed vertebrates. Moreover, the α1 and α2 domains, especially in amino acid residues presumably shaping a ligand-binding groove, were also highly conserved between placental and marsupial MR1. These findings suggest that the MR1 gene might have been established at its present location in a common ancestor of placental and marsupial mammals and that the shape of the putative ligand-binding groove in MR1 has been maintained, probably for presenting highly conserved component(s) of microbes to MAIT cells.