Deer mice (genus
Peromyscus
) are an emerging model for aging studies due to their longevity relative to rodents of similar size. Although
Peromyscus
species are well-represented in genetic, ...developmental, and behavioral studies, relatively few studies have investigated auditory sensitivity in this genus. Given the potential utility of
Peromyscus
for investigations of age-related changes to auditory function, we recorded auditory brainstem responses (ABRs) in two
Peromyscus
species,
P. californicus
, and
P. leucopus
, across the lifespan. We compared hearing sensitivity and ABR wave metrics measured in these species with measurements from
Mus musculus
(CBA/CaJ strain) to assess age-related effects on hearing across species. Recordings in young animals showed that all species had similar hearing ranges and thresholds with peak sensitivity ranging from 8 to 16 kHz; however,
P. californicus
and
P. leucopus
were more sensitive to frequencies below 8 kHz. Although
M. musculus
showed significant threshold shifts across a broad range of frequencies beginning at middle age and worsening among old individuals, older
Peromyscus
mice retained good sensitivity to sound across their lifespan. Middle-aged
P. leucopus
had comparable thresholds to young for frequencies below 24 kHz.
P. leucopus
also had notably large ABRs that were robust to age-related amplitude reductions, although response latencies increased with age. Old
P. californicus
were less sensitive to mid-range tones (8–16 kHz) than young individuals; however, there were no significant age-effects on ABR amplitudes or latencies in this species. These results indicate that longevity in
Peromyscus
mice may be correlated with delayed aging of the auditory system and highlight these species as promising candidates for longitudinal hearing research.
Lungless salamanders (Family Plethodontidae) form a highly speciose group that has undergone spectacular adaptive radiation to colonize a multitude of habitats. Substantial morphological variation in ...the otic region coupled with great ecological diversity within this clade make plethodontids an excellent model for exploring the ecomorphology of the amphibian ear. We examined the influence of habitat, development, and vision on inner ear morphology in 52 plethodontid species. We collected traditional and 3D geometric morphometric measurements to characterize variation in size and shape of the otic endocast and peripheral structures of the salamander ear. Phylogenetic comparative analyses demonstrate structural convergence in the inner ear across ecologically similar species. Species that dwell in spatially complex microhabitats exhibit robust, highly curved semicircular canals suggesting enhanced vestibular sense, whereas species with reduced visual systems demonstrate reduced canal curvature indicative of relaxed selection on the vestibulo-ocular reflex. Cave specialists show parallel enlargement of auditory-associated structures. The morphological correlates of ecology among diverse species reveal underlying evidence of habitat specialization in the inner ear and suggest that there exists physiological variation in the function of the salamander ear even in the apparent absence of selective pressures on the auditory system to support acoustic behavior.
Hearing without a tympanic ear Capshaw, Grace; Christensen-Dalsgaard, Jakob; Carr, Catherine E
Journal of experimental biology,
06/2022, Letnik:
225, Številka:
12
Journal Article
Recenzirano
Odprti dostop
The ability to sense and localize sound is so advantageous for survival that it is difficult to understand the almost 100 million year gap separating the appearance of early tetrapods and the ...emergence of an impedance-matching tympanic middle ear - which we normally regard as a prerequisite for sensitive hearing on land - in their descendants. Recent studies of hearing in extant atympanate vertebrates have provided significant insights into the ancestral state(s) and the early evolution of the terrestrial tetrapod auditory system. These reveal a mechanism for sound pressure detection and directional hearing in 'earless' atympanate vertebrates that may be generalizable to all tetrapods, including the earliest terrestrial species. Here, we review the structure and function of vertebrate tympanic middle ears and highlight the multiple acquisition and loss events that characterize the complex evolutionary history of this important sensory structure. We describe extratympanic pathways for sound transmission to the inner ear and synthesize findings from recent studies to propose a general mechanism for hearing in 'earless' atympanate vertebrates. Finally, we integrate these studies with research on tympanate species that may also rely on extratympanic mechanisms for acoustic reception of infrasound (<20 Hz) and with studies on human bone conduction mechanisms of hearing.
Interaural time differences (ITDs) are a major cue for sound localization and change with increasing head size. Since the barn owl's head width more than doubles in the month after hatching, we ...hypothesized that the development of their ITD detection circuit might be modified by experience. To test this, we raised owls with unilateral ear inserts that delayed and attenuated the acoustic signal, and then measured the ITD representation in the brainstem nucleus laminaris (NL) when they were adults. The ITD circuit is composed of delay line inputs to coincidence detectors, and we predicted that plastic changes would lead to shorter delays in the axons from the manipulated ear, and complementary shifts in ITD representation on the two sides. In owls that received ear inserts starting around P14, the maps of ITD shifted in the predicted direction, but only on the ipsilateral side, and only in those tonotopic regions that had
experienced auditory stimulation prior to insertion. The contralateral map did not change. Thus, experience-dependent plasticity of the ITD circuit occurs in NL, and our data suggest that ipsilateral and contralateral delays are independently regulated. As a result, altered auditory input during development leads to long-lasting changes in the representation of ITD.
The early life of barn owls is marked by increasing sensitivity to sound, and by increasing ITDs. Their prolonged post-hatch development allowed us to examine the role of altered auditory experience in the development of ITD detection circuits. We raised owls with a unilateral ear insert and found that their maps of ITD were altered by experience, but only in those tonotopic regions ipsilateral to the occluded ear that had not experienced auditory stimulation prior to insertion. This experience-induced plasticity allows the sound localization circuits to be customized to individual characteristics, such as the size of the head, and potentially to compensate for imbalanced hearing sensitivities between the left and right ears.
•Comparative research has driven many important discoveries in the auditory field.•There are many questions that a comparative approach is uniquely suited to address.•New tools allow for a diversity ...of measurements across species.
A rich history of comparative research in the auditory field has afforded a synthetic view of sound information processing by ears and brains. Some organisms have proven to be powerful models for human hearing due to fundamental similarities (e.g., well-matched hearing ranges), while others feature intriguing differences (e.g., atympanic ears) that invite further study. Work across diverse “non-traditional” organisms, from small mammals to avians to amphibians and beyond, continues to propel auditory science forward, netting a variety of biomedical and technological advances along the way. In this brief review, limited primarily to tetrapod vertebrates, we discuss the continued importance of comparative studies in hearing research from the periphery to central nervous system with a focus on outstanding questions such as mechanisms for sound capture, peripheral and central processing of directional/spatial information, and non-canonical auditory processing, including efferent and hormonal effects.
We investigated the temporal dynamics of acoustically interacting common tink frogs (Diasporus diastema), a species in which advertising males maintain large inter-individual distances that may ...influence call timing behaviours among nearest neighbours. This species produces advertisement calls in temporally structured bouts, with decreasing inter-note intervals that culminate in a 'burst' sequence of rapidly emitted notes. We broadcast playbacks of unaltered and temporally manipulated conspecific advertisement calls to focal male individuals vocalizing within triads (comprised of closely neighbouring focal and non-focal males and a more distant, outsider male). Focal males demonstrated rhythmic entrainment and adjusted their calling behaviour to overlap their call sequences with those of their nearest vocalizing neighbour, including the unaltered conspecific playback. When presented with a playback of conspecific calls lacking the natural temporal sequence, focal males reduced the duration of the silent interval between call bouts and reduced the number of notes in the burst phase of their call bout, indicating the significance of the multi-element temporally complex call bout structure in mediating male-male vocal interactions.
Due to their limited geographic distributions and specialized ecologies, cave species are often highly endemic and can be especially vulnerable to habitat degradation within and surrounding the cave ...systems they inhabit. We investigated the evolutionary history of the West Virginia Spring Salamander (
Gyrinophilus subterraneus)
, estimated the population trend from historic and current survey data, and assessed the current potential for water quality threats to the cave habitat. Our genomic data (mtDNA sequence and ddRADseq-derived SNPs) reveal two, distinct evolutionary lineages within General Davis Cave corresponding to
G. subterraneus
and its widely distributed sister species,
Gyrinophilus porphyriticus
, that are also differentiable based on morphological traits. Genomic models of evolutionary history strongly support asymmetric and continuous gene flow between the two lineages, and hybrid classification analyses identify only parental and first generation cross (F1) progeny. Collectively, these results point to a rare case of sympatric speciation occurring within the cave, leading to strong support for continuing to recognize
G. subterraneus
as a distinct and unique species. Due to its specialized habitat requirements, the complete distribution of
G. subterraneus
is unresolved, but using survey data in its type locality (and currently the only known occupied site), we find that the population within General Davis Cave has possibly declined over the last 45 years. Finally, our measures of cave and surface stream water quality did not reveal evidence of water quality impairment and provide important baselines for future monitoring. In addition, our unexpected finding of a hybrid zone and partial reproductive isolation between
G. subterraneus
and
G. porphyriticus
warrants further attention to better understand the evolutionary and conservation implications of occasional hybridization between the species.
The lepidopteran fauna of Massachusetts' offshore islands (USA), particularly Martha’s Vineyard and Nantucket, has been well characterized, and comprises intact assemblages of disjunct, regionally ...rare, habitat-specialized, and otherwise threatened species that have declined elsewhere in New England. These include the only persistent and extant population of Eacles imperialis Drury (Saturniidae: Ceratocampinae) in New England, one of at least three ceratocampines to have undergone partial or total extirpation from the region. Examining historical and recent records within two groups—Saturniidae and Sphingidae—that have exhibited varying degrees of flux over time, we compare these islands and identify taxonomic and ecological components of their faunas that appear historically volatile. After reviewing suspected agents of these declines, including the introduced generalist parasitoid Compsilura concinnata (Diptera: Tachinidae), we present preliminary tachinid capture data which suggest that C. concinnata has not been established where E. imperialis persists.
The ability to detect airborne sound using a pressure-transducing tympanic ear has evolved several times over the course of vertebrate history, suggesting that hearing is an advantageous modality and ...an informative model for sensory evolution. Amphibian hearing is especially interesting because these animals must negotiate water to land transitions. Salamanders are good animal models for the study of hearing, not only because they have a wide range of ear morphologies, but also because they have evolved extratympanic pathways for sound and vibration transmission. Here we suggest that sufficient extratympanic hearing in salamanders and reduced reliance on vocal communication has relaxed selection on the auditory system and allowed for the structural diversity of the salamander ear. Unique among salamanders is the family Plethodontidae, which is not only the most speciose and ecologically diverse family of salamanders, but also possesses a highly derived ear with great inter-specific variation. In this review, we provide an overview of historical and current research on acoustic behavior, auditory anatomy, evolution, and physiology. We highlight plethodontid salamanders as an informative model for study of extratympanic function and auditory evolution.
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