Sound transmission by the hyoid apparatus during echolocation in bats Chelsie C.G. Snipes1 and Richard T. Carter1 1 East Tennessee State University, Johnson City TN, USA 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. To test this hypothesis, we used µCT data, CAD editing software, and finite element analysis (FEA) to model the propagation of sound through the hyoid chain into the tympanic bones. This involved making digital segmentations from the µCT data of the tympanic bones and cartilaginous segments and converting it into a digital mesh body. Since the cartilaginous segments are not visible in CTs, we segmented the air in each gap and subsequently used a Boolean function in CAD software to fit each bony end into their respective cartilaginous segment. Further post-processing of the model included a reduction in the number of facets bodies and smoothing surfaces which allowed us to convert it into a solid body model. The solid body geometry was then uploaded into FEA software and assigned material properties for cortical bone, cartilage, and bulla. Additional biomechanical data, including Young’s Modulus, Poisson’s ratio, and speed of sound through each material were defined in previous literature. We ran two FEA analysis with our model: the first was an acoustic analysis that modelled sound propagation through our material (bone and cartilage), and the second was a coupled modal and structural analysis that modelled resonant behavior and sound pressure wave propagation from the hyoid body to the tympanic bones. Our models support the hypothesis that bats use this physical connection between the larynx and auditory bulla to transfer sound (mechanical excitation). Our models show both pressure waves and vibration due to resonance could be used to transfer this signal and this resonance behavior can be modulated by restraining the hyoid apparatus, perhaps through muscle contraction. We propose that by modulating the resonant behavior of the hyoid apparatus, bats can selectively filter which frequencies of sound are transferred from the larynx to the auditory bulla during echolocation signal production.

Circadian clocks are endogenous time keeping mechanisms that are ubiquitous among animals. They enable coordination of many essential biological and metabolic processes in relation to the 24 hour light cycle on earth. However, there are many habitats on earth that are not subject to this light cycle. This study aims to look at the potential genetic drift of the circadian rhythm of a subterranean spider, Meta ovalis, as well as gathering general natural history information on this under-studied spider. This study will fill general gaps in knowledge of this spider and its habitat, highlight the importance of studying organisms within a subterranean environment, and place importance on cave conservation and acquiring knowledge of these specialized, and sensitive species. This study integrates circadian and foraging theory to evaluate species as circadian specialists and generalists based on how narrowly or widely their activity is spread over the 24 h cycle. We suggest that M. ovalis benefits from a generalist strategy, showing small bursts of focused activity widely dispersed across the 24 h cycle, allowing it to capture prey opportunistically whenever it is available. Live spiders were collected from area caves, monitored in an environment controlled for light and temperature, and returned to their cave of origin. The activity of each spider was analyzed for differences in circadian activity among and between populations to determine if there is a significant drift of the circadian strategy between isolated populations of Meta ovalis. We expect to see a different circadian strategy implemented between populations due to drift from the spiders being isolated from other populations.

Most eukaryotic organisms have an internal circadian clock which allows them to maintain their physiological and behavioral cycles in phase with the 24-hour day. The ability to synchronize with (entrain to) the 24-hour day prevents mismatch between the internal circadian clock and the daily cycle which could lead to serious health risks. Some spider species, including Parasteatoda tepidariorum, appear to be exempt from the negative consequences of being out of phase with the 24-hour day. Parasteatoda tepidariorum, the common house spider, is a nocturnal species that consistently demonstrates a short-period circadian clock averaging 21.6 hours when left in constant darkness, yet they are able to entrain to the 24-hour light cycle. Here we test if these spiders are able to use cues (Zeitgebers) other than light to entrain to the 24-hour day. These non-photic Zeitgebers included food, disturbance, and temperature changes. The spiders were assigned into groups which received the given external cues at 24-hour intervals for 7 days followed by 7 days without any external cues. Food, disturbance, and temperature were not found to be effective Zeitgebers for the spiders’ entrainment. There were significant results between random feedings with consistent scheduled feedings which suggests that these spiders were able to manipulate the duration of activity based on the consistency and regularity of a food source. Adjusting the span of activity based on availability of food sources would be advantageous for spiders considering that prey availability in natural environments may not be rhythmic. Given that these spiders tend to build webs in dark secluded spaces, it would be a particular advantage for them to be able to use an environmental cue in addition to light to entrain their internal clocks. However, our data to date suggest otherwise.

Many organisms are known to reach high levels of endemism and biodiversity in the temperate forests of Southern Appalachia, especially in the dense forests and rugged terrain of the Blue Ridge physiographic province. Many plants and fungi reach their highest levels of biodiversity in these mountains, as does one group of vertebrates: the lungless salamanders, Plethodontidae. This family of salamanders hosts the most species of any other group of salamanders on earth and has adapted to a wide range of habitats. Only two of the approximately twenty-seven known genera are not found in North or South America, and while we know much about the modern-day biology of this family, few fossils older than ~15,000 years have been recovered, complicating our understanding of the historical distribution of this group and the timing of key evolutionary events within the family. Recently discovered salamander fossils from the Gray Fossil Site provide the foundation of this project. We describe these exceptionally large plethodontid remains to a new genus that belongs to the group containing dusky salamanders, or desmognathans. The morphology of the fossil material resembles Phaeognathus hubrichti, an extant burrowing species from southern Alabama with a suite of primitive characteristics. Comparison of the fossil material to modern desmognathans using geometric statistical methods has revealed that the extinct form was likely similar in lifestyle to P. hubrichti, but considerably larger. It was unparalleled in the southern Appalachians in terms of size and ecology, and reveals a more complex evolutionary history for desmognathan salamanders.

To avoid masking incoming echoes with outgoing calls, bats use a low duty cycle (LDC) or high duty cycle (HDC) echolocation strategy. LDC echolocation is the most common and involves short pulses of broadband sound followed by relatively long periods of silence. In contrast, HDC echolocators emit long, narrowband sounds with short periods of silence and use Doppler shifts to detect the relative speed of prey. HDC echolocators are almost exclusively found in the families Rhinolophidae and Hipposidaridae. However, there are two known exceptions that have evolved echolocation strategies independent of the families of which they reside: Pternotus parnelli is from an LDC family but uses HDC echolocation, and conversely, Coelops frithii is from an HDC family but uses LDC echolocation. In our previous work, we used engineering software to model sound transmission from the larynx to the auditory bulla via the stylohyal-tympanic bone articulation and found that sound transmitted through the bony chain during echolocation call emission is likely loud enough for bats to hear. We also noticed differences in the morphology of the stylohyal and its placement on the tympanic bulla that might correlate with echolocation strategy. Pteronotus parnelli and C. frithii, having evolved echolocation strategies that differ from the other species in their respective families, provide the opportunity to test whether these morphologies are simply “evolutionary baggage” or driven by a selective pressure associated with function. To test this, we used µCT image data to compare the morphology of the stylohyal bones from P. parnelli, C. frithii, and other LDC and HDC echolocators. Preliminary results show that HDC echolocators have a stylohyal that sits on the medial side of the bulla, while the stylohyal in LDC echolocators sits on the lateral side of the bulla. The stylohyal in P. parnelli and C. frithi appear to have characteristics of both HDC and LDC echolocators. Further analysis will include a Multivariant Functional Shape Analysis (MFSA) to determine if these morphological differences are statistically significant and identify what variant(s) are likely driving these differences. Lastly, digital 3D models from each bat species have been built from µCT data to test for functional differences via acoustic engineering simulations. Since bone conducted sound can reach the cochlea through direct stimulation or stimulation of the eardrum, we predict that an LDC echolocator, with its stylohyal sitting on the lateral side of the bulla, will transmit sound to the cochlea more effectively through the eardrum. And given the stylohyal in HDC echolocators sits on the medial side of the bulla, we expect to see better direct stimulation of the cochlea than that of a LDC echolocator. This research uses an integrative approach to address a long-held assumption concerning the function of the stylohyal-tympanic bone articulation in laryngeally echolocating bats.

The hyoid apparatus in laryngeally echolocating bats is unique as it forms a mechanical connection between the larynx and auditory bullae which has been hypothesized to transfer the outgoing echolocation call to the middle ear during call emission. Previous finite element modeling (FEM) found that hyoid-borne sound can reach the bulla at an amplitude likely heard by echolocating bats; however, that study did not model how or if the signal could reach the inner ear (or cochlea). One route that sound could take is via stimulation of the eardrum – similarly to that of air-conducted sound. We used µCT data to build models of the hyoid apparatus and middle ear from six species of bats with variable morphology. Using FEM, we ran harmonic response analyses to measure the vibroacoustic response of the tympanic membrane to hyoid-borne sound generated during echolocation and found that hyoid-borne sound in all six species stimulated the eardrum within a range likely heard by bats. Although there was variation in the efficiency between models at higher frequencies, there are no obvious morphological patterns to account for it. This suggests that hyoid morphology in laryngeal echolocators is likely driven by other associated functions and warrants further inquiry. Note: This work was published open access in the Journal of Integrative Organismal Biology (https://doi.org/10.1093/iob/obad004)

Niche partitioning is a major component in understanding community ecology and how different species divide limited environmental resources, enabling them to coexist. Temporal niche partitioning has been widely studied in a broad sense, such as in species that forage on similar nutritional sources dividing activity along diurnal and nocturnal classifications. Here, we approach this temporal niche partitioning with higher resolution to investigate partitioning between species within the same broad temporal and foraging niche. Two species of diurnal orb-weaving spiders (Araneae: Araneidae), Verrucosa arenata and Micrathena gracilis, both construct their orbs in spatially similar locations throughout the understory of deciduous forests in the morning, forage on flying insects throughout the day, and retreat in the evening. However, despite consisting of what appear to be roughly similar total lengths of adhesive silk in the capture spiral, overall orb structure is starkly different: V. arenata orbs are relatively large in diameter and sparse with capture threads; M. gracilis orbs, condensed in diameter and tightly coiled. What other differences might distinguish foraging strategy within this same niche? With extensive observation in their natural environment, we have found that these two species employ two distinct strategies by modulating behavior and orb structure: V. arenata construct orbs earlier in the day, resulting in a longer foraging period. However, V. arenata webs are more likely to be destroyed during the day such that there is a higher variance in foraging duration in V. arenata. We also found that V. arenata actively capture and consume more large prey and that M. gracilis more passively capture and consume small prey more reliably. These data suggest that these species have evolved different foraging strategies with V. arenata being risk-prone and M. gracilis being risk-averse. This study provides a more nuanced analysis of niche partitioning between species occupying otherwise similar temporal, habitat, and foraging niches.

<p>Despite being distributed worldwide and easily collected, the biology, ecology, and taxonomy of Ptiliidae Heer, 1843, or featherwing beetles, have not been well studied. In a study from 2007 to 2009, Ptiliidae were extracted from various polypore fungi collected throughout Costa Rica in an effort to expand biogeographic knowledge of Ptiliidae. Fungi and Ptiliidae were identified to genera and collection sites mapped. Beetle genera are able to inhabit different polypore genera and were found at a higher rate of co-occurrence than reported in previous studies. We identified <i>Cylindrosella costariciensis </i><b>sp. n.</b>, with the potential of two more new species to be described.</p>

<p>  </p> <p>Evolution is the foundation for all of biology. However, our approaches and understanding of evolution—simply, the change of allele frequencies from one generation to the next—have themselves evolved over time. In this dissertation I explore multiple approaches to understand evolution and the consequences of evolution across variable scales and study organisms. First, I use meta-analytic techniques and Bayesian hierarchical models to investigate the phenotypic consequences of two forms of cryptic local adaptation, co- and countergradient variation, by leveraging a decades-old quantitative genetics approach (Chapter 1). I find large effects for both co- and countergradient variation, however they are obscured in natural settings by concurrent large environmental effects. I also show that these large effects are ubiquitous across phenotypic traits, organisms, and environmental gradients, suggesting that while similar phenotypes may be the evolutionary end point, the mechanisms to achieve those phenotypes likely vary. In the following chapter I explore the rapid evolution of a unique and understudied species introduction, pink salmon (<em>Oncorhynchus gorbuscha</em>) in the Great Lakes. Pink salmon were introduced into Lake Superior in a single introduction event and have broken two obligate life histories, anadromy (though they treat the Great Lakes like surrogate oceans) and their fixed two-year life cycle, making them ripe subjects for contemporary evolution. Using whole-genome sequence data, I first investigate the effects of a genetic drift in the form of a bottleneck at introduction and characterize the subsequent loss of genetic diversity (Chapter 2). I show that despite a large loss of genetic diversity, pink salmon also rapidly adapted to their novel environment based on signals of putative selection across numerous regions of the genome, particularly in a period gene associated with their daily circadian clock (<em>per2</em>). Next, I explore how genome structure likely aided adaptation by pink salmon to the Great Lakes, providing evidence that a supergene (~29 Mbp) containing an inversion on chromosome 10 swept to near fixation in the Great Lakes (Chapter 3) and likely aided in osmoregulatory adaptation to this novel environment. Finally, I end with a short perspective chapter (Chapter 4) where I highlight potential future research directions for each of the previous chapters. Together, this research investigates the drivers and consequences of evolution across multiple scales and shows the powerful effect of genetic drift and genetic adaptation in shaping the genomic and phenotypic attributes of populations.</p>