Biology subjects

Smith, S. K.

Publications and source records attributed to Smith, S. K..

6 recordsLinked to original sources

bioRxiv2025

Mechanisms and control of a novel vocalization: the singing mouse song is a whistle that depends on air sac inflation

Identifying variation in vocal morphology and sound production mechanisms is essential to understanding vocal diversity. Rodents provide an ideal system for exploring this variation as they use multiple sound production mechanisms and have novel vocal structures whose morphology varies interspecifically. Here, we describe the laryngeal morphology and identify the sound production mechanism of Alstons singing mouse (Scotinomys teguina), which produce stereotyped songs. We used micro-computed tomography to examine laryngeal morphology and manipulated excised larynges and surgically ablated a laryngeal muscle to determine sound production mechanism and frequency control. Laryngeal manipulations indicated that a whistle mechanism, likely an edge tone or shallow cavity, produces song. Singing mouse whistles are unique compared to other rodents because they rely on the inflation of an enlarged intralaryngeal air sac called the ventral pouch. Whistle frequency can be controlled by ventral pouch inflation, laryngeal airflow, and by cricothyroid muscle action. Cricothyroid ablation inhibited frequency modulation in vivo, suggesting that singing mice use this muscle during singing. Singing mouse laryngeal morphology and vocal mechanism are distinct from other Neotomids; instead of using vocal fold oscillations for loud, long-distance calls and whistles for close-range interactions, singing mice appear to use whistles for distant and close exchanges by inflating their intralaryngeal air sac. Air sacs have evolved repeatedly among vocalizing mammals and our results indicate a new role for these structures in generating sound. Together, our results expand on an emerging story of how biomechanic and morphological variation contributes to vocal diversity.

physiology↗

bioRxiv2023

Tail length in male versus female fox squirrels (Sciurus niger)

BackgroundArboreal mammals rely on their tails to aid in balance while maneuvering complex habitats. Females experience additional challenges to locomotion due to reproductive demands including altered body mass and/or body shape, which leads to shifts in center of mass. Without compensation, this may increase the risk of losing balance and falling out of trees. We tested the hypothesis that female squirrels have longer tails than males to offset shifts in center of mass that may result from pregnancy. ResultsMorphological data were collected from 57 fox squirrels (Sciurus niger) in northern Indiana in summer 2019 and 2021. Although our initial t-test analysis of relative tail length (RTL) showed that female squirrels had longer tails than males (p = 0.02), a subsequent ANCOVA that controlled for effect of body length indicated no significant effect of sex on tail length (p = 0.42). ConclusionsThe results of this study demonstrate the potential impacts of different analysis methods on overall understanding of organismal functional morphology and are an important addition to the literature on tail form and function, which remains poorly understood compared to other appendages.

zoology↗

bioRxiv2022

De novo assembly and annotation of the singing mouse genome

BackgroundDeveloping genomic resources for a diverse range of species is an important step towards understanding the mechanisms underlying complex traits.Specifically, organisms that exhibit unique, accessible phenotypes-of-interests, allow researchers to address questions that may be ill-suited to traditional model organisms. We sequenced the genome and transcriptome of Alstons singing mouse (Scotinomys teguina), an emerging model for social cognition and vocal communication. In addition to producing advertisement songs used for mate attraction and male-male competition, these rodents are diurnal, live at high-altitudes, and are obligate insectivores, providing opportunities to explore diverse physiological, ecological, and evolutionary questions. ResultsUsing PromethION, Illumina, and PacBio sequencing, we produced an annotated genome and transcriptome, which were validated using gene expression and functional enrichment analyses. To assess the usefulness of our assemblies, we performed single nuclei sequencing on cells of the orofacial motor cortex, a brain region implicated in song coordination, identifying 12 cell types. ConclusionsThese resources will provide the opportunity to identify the molecular basis of complex traits in singing mice as well as to contribute data that can be used for large-scale comparative analyses.

genomics↗

bioRxiv2021

Mapping the vocal circuitry of Alston's singing mouse with pseudorabies virus

Vocalizations, like many social displays, are often elaborate, rhythmically structured behaviors that are modulated by a complex combination of cues. Vocal motor patterns require close coordination of neural circuits governing the muscles of the larynx, jaw, and respiratory system. In the elaborate vocalization of Alstons singing mouse (Scotinomys teguina), for example, each note of its rapid, frequency-modulated trill is accompanied by equally rapid modulation of breath and gape. To elucidate the neural circuitry underlying this behavior, we introduced the polysynaptic retrograde neuronal tracer pseudorabies virus (PRV) into the cricothyroid and digastricus muscles, which control frequency modulation and jaw opening respectively. Each virus singly labels ipsilateral motoneurons (nucleus ambiguous for cricothyroid, and motor trigeminal nucleus for digastricus). We find that the two isogenic viruses heavily and bilaterally co-label neurons in the gigantocellular reticular formation, a putative central pattern generator. The viruses also show strong co-labeling in compartments of the midbrain including the ventrolateral periaqueductal grey and the parabrachial nucleus, two structures strongly implicated in vocalizations. In the forebrain, regions important to social cognition and energy balance both exhibit extensive co-labeling. This includes the paraventricular and arcuate nuclei of the hypothalamus, the lateral hypothalamus, preoptic area, extended amygdala, central amygdala, and the bed nucleus of the stria terminalis. Finally, we find doubly labeled neurons in M1 motor cortex previously described as laryngeal, as well as in the prelimbic cortex, which indicate these cortical regions play a role in vocal production. Although we observe some novel patterns of double-labelling, the progress of both viruses is broadly consistent with vertebrate-general patterns of vocal circuitry, as well as with circuit models derived from primate literature.

neuroscience↗

bioRxiv2021

BMP signaling underlies the craniofacial heterochrony in phyllostomid bats, a hyperdiverse mammal group

The potential for variation and the capacity to evolve in response to ecological opportunity are important aspects of an adaptive radiation. Identifying the origin of phenotypic variation, in which natural selection might act upon, is a major goal of evolutionary developmental biology. The New World leaf-nosed bats (phyllostomids) are a textbook example of an adaptive radiation. Their cranial morphology is diverse along relative facial length, which is related to their diets. We previously used geometric morphometrics to reveal peramorphosis, a type of heterochrony, in the cranial evolution among phyllostomid bats. We then demonstrated that the mechanism of peramorphic diversity in phyllostomid rostrum length resulted from altered cellular proliferation. Here, we investigate the progenitors of the face, the cranial neural crest, and a key signaling pathway related to their proliferation and differentiation into mature tissues: the bone morphogenetic protein (BMP). With geometric morphometrics, immunofluorescence, and confocal imaging--in three phyllostomid species and one outgroup bat species--we show the molecular patterns that underlie the adaptive and innovative traits seen in phyllostomid bats. Then, with mouse genetics, we mimic the BMP molecular pattern observed in nectar feeding bats and recapitulate the elongated morphological variation in mice. Surprisingly, we also observe an expansion in the nose-tip of mice, akin to the expanding leaf-nose tissue in phyllostomid bats. These data, combined with the mouse genetics literature on BMP signaling, suggest the BMP developmental pathway plays a central role in shaping the craniofacial variation necessary for adaptation in bats. Further, we speculate that the BMP signaling pathway could underlie other bizarre facial phenotypes in mammals that are derived from frontonasal mesenchyme, such as the proboscis. Overall, this study combines a comparative framework to developmental data, with a genetic approach, to directly investigate the role of development on complex morphology.

evolutionary biology↗

bioRxiv2020

Presynaptic accumulation of α-synuclein causes synaptopathy and progressive neurodegeneration

Alpha-synuclein (-syn) mislocalisation and accumulation in intracellular inclusions is the major pathological hallmark of degenerative synucleinopathies, including Parkinsons disease, Parkinsons disease with Dementia and Dementia with Lewy Bodies. Typical symptoms are behavioural abnormalities including motor deficits that mark disease progression, while non-motor symptoms and synaptic deficits are already apparent during the early stages of disease. Synucleinopathies have therefore been considered synaptopathies that exhibit synaptic dysfunction prior to neurodegeneration. However, the mechanisms and events underlying synaptopathy are largely unknown. Here we investigated the cascade of pathological events underlying -syn accumulation and toxicity in a Drosophila model of synucleinopathy by employing a combination of histological, biochemical, behavioural and electrophysiological assays. Our findings demonstrate that targeted expression of human -syn leads to its accumulation in presynaptic terminals that caused downregulation of synaptic proteins, Cysteine String Protein, Synapsin, and Syntaxin 1A, and a reduction in the number of Bruchpilot puncta, the core component of the presynaptic active zone essential for its structural integrity and function. These -syn-mediated presynaptic alterations resulted in impaired neuronal function, which triggered behavioural deficits in ageing Drosophila that occurred prior to progressive degeneration of dopaminergic neurons. Comparable alterations in presynaptic active zone protein were found in patient brain samples of Dementia with Lewy Bodies. Together, these findings demonstrate that presynaptic accumulation of -syn impairs the active zone and neuronal function, which together cause synaptopathy that results in behavioural deficits and the progressive loss of dopaminergic neurons. This sequence of events resembles the cytological and behavioural phenotypes that characterise the onset and progression of synucleinopathies, suggesting that -syn mediated synaptopathy is an initiating cause of age-related neurodegeneration.

neuroscience↗