Soil properties and the distribution of the endangered Juliana's golden mole

The endangered Juliana's golden mole Neamblysomus julianae occurs in three small, geographically isolated populations within South Africa. As a sand-swimmer, it is a habitat specialist and has a highly fragmented distribution within each population. There is a need for a conservation action plan for this species, but this is difficult because of the dearth of knowledge of its biology, including its habitat characteristics. To better understand its patchy distribution, we selected 48 plots that were occupied or unoccupied by golden moles and measured the soil properties in each plot. The size distribution of sand particles influenced the density and compactability of the soil, and both were positively correlated with the presence of golden moles. These soil characteristics are thus vital in understanding and describing the distribution of this cryptic species.     

Bone conduction and seismic sensitivity in golden moles (Chrysochloridae)

Some genera of golden moles are known to possess enormously hypertrophied auditory ossicles. These structures have been implicated as potentially mediating a form of inertial bone conduction, used by the golden mole to detect seismic vibrations. A simple model of ossicular inertial bone conduction, based on an existing model of the human middle ear from the literature, was used in an attempt to examine vibrational sensitivity in these animals. Those golden moles with hypertrophied ossicles are predicted to possess a sensitive inertial bone conduction response at frequencies below a few hundred hertz, whereas species lacking these middle ear adaptations are predicted to have a far less sensitive response in this ecologically important frequency range. An alternative mode of inertial bone conduction in golden moles, potentially conferring sensitivity to vertically-polarized seismic vibrations such as Rayleigh waves, is proposed. Certain behaviours of golden moles described in the literature are interpreted as augmenting seismic sensitivity.     

Acoustic communication and burrow acoustics are reflected in the ear morphology of the coruro (Spalacopus cyanus, Octodontidae), a social fossorial rodent

We studied the middle and inner ears of seven adult coruros (Spalacopus cyanus), subterranean and social rodents from central Chile, using free-hand dissection and routine staining techniques. Middle ear parameters that were focused on here (enlarged bullae and eardrums, ossicles of the "freely mobile type") are believed to enhance hearing sensitivity at lower frequencies. The organ of Corti was of a common mammalian type and revealed three peaks of higher inner hair cell densities. Based on a position frequency map, frequencies were assigned to the respective peaks along the basilar membrane. The first peak at around 300-400 Hz is discussed with respect to the burrow acoustics, while the peak around 10-20 kHz is probably a plesiomorphic feature. The most pronounced peak at around 2 kHz reflects the frequency at which the main energy of vocal communication occurs. The morphology of the ear of the coruro corresponds to the typical pattern seen in subterranean rodents (low frequency and low-sensitivity hearers), yet, at the same time, it also deviates from it in several functionally relevant features.     

Ossicular density in golden moles (Chrysochloridae)

The densities of middle ear ossicles of golden moles (family Chrysochloridae, order Afrosoricida) were measured using the buoyancy method. The internal structure of the malleus was examined by high-resolution computed tomography, and solid-state NMR was used to determine relative phosphorus content. The malleus density of the desert golden mole Eremitalpa granti (2.44 g/cm³) was found to be higher than that reported in the literature for any other terrestrial mammal, whereas the ossicles of other golden mole species are not unusually dense. The increased density in Eremitalpa mallei is apparently related both to a relative paucity of internal vascularization and to a high level of mineralization. This high density is expected to augment inertial bone conduction, used for the detection of seismic vibrations, while limiting the skull modifications needed to accommodate the disproportionately large malleus. The mallei of the two subspecies of E. granti, E. g. granti and E. g. namibensis, were found to differ considerably from one another in both size and shape.     

What did Morganucodon hear?

The structure of the middle and inner ear of Morganucodon , one of the oldest known mammals, is reviewed and compared to the structure of the ears of extant mammals, reptiles and birds with known auditory capabilities. Specifically, allometric relationships between ear dimensions (basilar-membrane length, tympanic-membrane area and stapes-footplate area) and specific features of the audiogram are defined in extant ears. These relationships are then used to make several predictions of auditory function in Morganucodon. The results point out that the ear structures of Morganucodon–Art similar in dimensions to ear structures in both extant small mammals–with predominantly high-frequency (10 kHz) auditory capabilities, and reptiles and birds- with better low and middle-frequency hearing (< 5 kHz). Although the allometric analysis cannot by itself determine whether Morganucodon heard more like present-day small mammals, or birds and reptiles, the apparent stiffness of the Morganucodon middle ear is both more consistent with the high-frequency mammalian middle ear and would act to decrease the sensitivity of a bird-reptile middle ear to low-frequency sound. Several likely hearing scenarios for Morganucodon are defined, including a scenario in which these animals had ears like those of modern small mammals that are selectively sensitive to high-frequency sounds, and a second scenario in which the Morganucodon ear was moderately sensitive to sounds of a narrow middle-frequency range (5–7 kHz) and relatively insensitive to sounds of higher or lower frequency. The evidence needed to substantiate either scenario includes some objective measure of the stiffness of the Morganucodon ossicular system, while a key datum needed to distinguish between the two hypotheses includes confirmation of the presence or absence of a cochlear lamina in the Morganucodon inner ear.     

Insights into torpor and behavioural thermoregulation of the endangered Juliana's golden mole

The cryptic, subterranean ways of golden moles (Chrysochloridae) hamper studies of their biology in the field. Ten species appear on the IUCN red list, but the dearth of information available for most inhibits effective conservation planning. New techniques are consequently required to further our understanding and facilitate informed conservation management decisions. We studied the endangered Juliana's golden mole Neamblysomus julianae and aimed to evaluate the feasibility of using implantable temperature sensing transmitters to remotely acquire physiological and behavioural data. We also aimed to assess potential body temperature ( T _b) fluctuations in relation to ambient soil temperature ( T _a) in order to assess the potential use of torpor. Hourly observations revealed that T _b was remarkably changeable, ranging from 27 to 33 °C. In several instances T _b declined during periods of low T _a. Such 'shallow torpor' may result in a daily energy saving of c . 20%. Behavioural thermoregulation was used during periods of high T _a by selecting cooler microclimates, while passive heating was used to raise T _b early morning when T _a was increasing. In contrast to anecdotal reports of nocturnal patterns of activity, our results suggest that activity is flexible, being primarily dependent on T _a. These results exemplify how behavioural patterns and microclimatic conditions can be examined in this and other subterranean mammal species, the results of which can be used in the urgently required conservation planning of endangered Chrysochlorid species.     

Atmospheric air vs. normal middle ear gas: Effects on in vitro growth and collagen synthesis in normal middle ear fibroblasts

Summary The present study was undertaken to quantitate the effects of atmospheric air and normal middle ear gas on cultured fibroblasts obtained from normal rabbit middle ear mucosa. The cells were exposed to three different gas compositions: 7% O₂:5% CO₂:88% N₂, 21% O₂:5% CO₂:74% N₂, and 75% O₂:5% CO₂:20% N₂. The growth was monitored by measuring the total content of cell protein, the amount of DNA, and the cell division activity. The activity of the synthetic apparatus was determined by the collagen synthesis. For comparison, rabbit skin fibroblasts were grown under identical conditions. The results demonstrated significantly higher replication rate of middle ear fibroblasts at 7% oxygen than at atmospheric air whereas the collagen synthesis was significantly lower at 7%. Furthermore, the responses varied significantly between rabbit middle ear and rabbit skin fibroblasts. Thus the present study substantiates the hypothesis of an influence of atmospheric air on the middle ear mucosa which might be of importance, e.g., in relation to insertion of ventilation tubes or longstanding perforations of the tympanic membrane in otitis media.     

The influence of muscles activation on the dynamical behaviour of the tympano-ossicular system of the middle ear

The human ear is a complex biomechanical system and is divided into three parts: outer, middle and inner ear. The middle ear is formed by ossicles (malleus, incus and stapes), ligaments, muscles and tendons, which transfers sound vibrations from the eardrum to the inner ear, linking with mastoid and Eustachian tube. In this work, a finite element modelling of the tympano-ossicular system of the middle ear was developed. A dynamic study based on a structural response to harmonic vibrations, for a sound pressure level (SPL) of 110, 120 and 130 dB SPL applied in the eardrum, is presented. The connection between the ossicles is made using a contact formulation. The model includes the different ligaments considering its hyperelastic behaviour. The activation of the muscles is based on the constitutive model proposed by previous work. The harmonic responses of displacement and pressure obtained on the stapes footplate, for a frequency range between 100 Hz and 10 kHz, are obtained simulating the muscle activation. The results are compared considering the passive and active states. The results are discussed and they are in accordance with audiological data published with reference to the effects of the middle ear muscles contraction.     

Morphology of the middle ear of golden moles (Chrysochloridae)

The middle ear structures of nine species of golden moles (family Chrysochloridae) were examined under the light microscope. Auditory structures of several of these species are described here for the first time in detail, the emphasis being on the ossicular apparatus. Confirming previous observations, some golden moles (e.g. Amblysomus species) have ossicles of a morphology typical of mammals, whereas others ( Chrysospalax , Chrysochloris , Cryptochloris and Eremitalpa species) have enormously hypertrophied mallei. Golden moles differ in the nature and extent of the interbullar connection, the shape of the tympanic membrane and that of the manubrium. The stapes has an unusual orientation, projecting dorsomedially from the incus. It has been proposed that hypertrophied ossicles in golden moles are adapted towards the detection of seismic vibrations. The functional morphology of the middle ear apparatus is reconsidered in this light, and it is proposed that adaptations towards low-frequency airborne hearing might have predisposed golden moles towards the evolution of seismic sensitivity through inertial bone conduction. The morphology of the middle ear apparatus sheds little light on the disputed ordinal position of the Chrysochloridae.