Detection of hydrodynamic stimuli by the postcranial body of Florida manatees (Trichechus manatus latirostris) A Neuroethology, sensory, neural, and behavioral physiology

Manatees live in shallow, frequently turbid waters. The sensory means by which they navigate in these conditions are unknown. Poor visual acuity, lack of echo- location, and modest chemosensation suggest that other modalities play an important role. Rich innervation of sen- sory hairs that cover the entire body and enlarged soma- tosensory areas of the brain suggest that tactile senses are good candidates. Previous tests of detection of underwater vibratory stimuli indicated that they use passive movement of the hairs to detect particle displacements in the vicinity of a micron or less for frequencies from 10 to 150 Hz. In the current study, hydrodynamic stimuli were created by a sinusoidally oscillating sphere that generated a dipole field at frequencies from 5 to 150 Hz. Go/no-go tests of manatee postcranial mechanoreception of hydrodynamic stimuli indicated excellent sensitivity but about an order of magnitude less than the facial region. When the vibrissae were trimmed, detection thresholds were elevated, suggest- ing that the vibrissae were an important means by which detection occurred. Manatees were also highly accurate in two-choice directional discrimination: greater than 90% correct at all frequencies tested. We hypothesize that mana- tees utilize vibrissae as a three-dimensional array to detect and localize low-frequency hydrodynamic stimul

The Use of Multiple Sensory Modalities by the Antillean Manatee (Trichechus Manatus Manatus) To Locate Food in Their Natural Environments

Manatees are herbivorous aquatic mammals found in the coastal and inland waters of the Atlantic Ocean. All three manatee species are currently listed as vulnerable on the IUCN red list and there still remains much unknown about their ecology. It is currently unknown what sensory modalities manatees use to locate their food in the wild. A literature review of the Paenungulata clade (sirenians, proboscideans, and hyracoideans) was conducted in order to compare and contrast what is known about the sensory modalities of the clade, to better understand the sensory modalities of manatees, particularly the ones they use to locate their food. Manatees have a higher frequency range for hearing than elephants, who have the best low-frequency hearing range known to mammals; hearing range of hyrax is unknown. All members of Paenungulata have vibrissae assisting in tactile abilities and potentially compensate for other senses such as hearing or vision. The ability to smell in manatees and hyrax is unknown, but elephants have been found to have an excellent sense of smell. Manatees, elephants, and hyrax have dichromatic vision. A preliminary experiment was designed to test manatee feeding modalities in the wild. The objectives of this study were to determine if the proposed methodology, modified for an aquatic environment from Renda & Roux (2017), was capable of testing manatee sensory use by limiting the sensory cues provided. Sensory modalities used in locating food were tested in two ways: when they know where the food is located, within a short distance, and when the food is placed randomly throughout their habitat, at long distances. In this study, we were able to show that the experimental design works, and provide preliminary data. In the short distance dichotomous choice trials, the percent of correct choices were 67% for the chemoreception + vision, 60% for chemoreception only, and 60% for vision only, with 50% being the rate of chance. For long distance experiments, the mean minimum time in hours it took manatees to consume the food placed randomly along their habitat of San San-Pond Sak River, Panama was 12.0 hours for chemoreception + vision, more than 22 hours for chemoreception only, and 6.89 hours for the control (no box). Due to the small sample size, no definitive conclusion could be made as to which sensory modality manatees use to find food, but our results support the idea that manatees use multiple modalities, chemoreception + vision, to locate food. Additional trials are needed in order to perform statistical analysis on the data

Innervation Patterns of Mystacial Vibrissae Support Active Touch Behaviors in California Sea Lions (Zalophus californianus)

Vibrissae, or whiskers, are highly developed sensory structures found in mammals. The follicles are referred to as Follicle Sinus Complexes (F-SC) due to the blood-filled sinuses. F-SCs are highly innervated compared to pelage. The most wellknown group of vibrissae, mystacial vibrissae, are found around the muzzle in mammals. Pinnipeds have the largest and most innervated vibrissae of any mammal. More aquatic mammals tend to have larger F-SCs and greater innervation investment (axons per FSC). Behavioral performance studies have shown that California sea lions Zalophus californianus (CSL, an otariid) excel at haptics whereas harbor seals Phoca vitulina (a phocid) excel at hydrodynamic trail following. The data presented in this thesis will infer vibrissal function from these studies. To date there has been no thorough investigation of innervation investment in an otariid. The objectives of this study were to investigate the innervation of the largest F-SCs, compare the innervation and microstructure to the most medial F-SCs, and compare the dorsal to ventral F-SCs. Follicles were dissected from tissues obtained from stranding programs and processed for histology. Axons were counted from wet mounted cross-sections. Asymmetry of axon bundles was present in all F-SC cross sections and have not been described before as well as blood vessels seen entering the DC of the LCS. There was a mean of 75±5 F-SCs per face muzzle. Innervation increased from medial (705 ±125 axons/F-SC) to lateral (1447±154) as well as from dorsal (541 ± 60) to the ventral F-SCs (1493 ± 327). Lateral F-SCs axon counts were similar to those in other pinniped studies. The total innervation from lateral axon counts (108,525 axons) agree with other studies but total innervation from all six areas (86,042 axons) was 20% less than values from only lateral F-SCs. Axon density of medial F-SCs were significantly more than lateral F-SCs. This finding is congruent with CSL behavioral performance data that suggest they excel at haptic touch. We found no substantial evidence to differentiate which F-SCs fall into micro- or microvibrissae categories. To date no study has investigated the dorsal-ventral micro anatomical and innervation patterns in any pinniped

MECHANOSENSORY FEEDBACK FOR FLIGHT CONTROL AND PREY CAPTURE IN THE ECHOLOCATING BAT

Throughout the animal kingdom, organisms have evolved neural systems that process biologically relevant stimuli to guide a wide range of species-specific behaviors. Bats, comprising 25% of mammalian species, rely on diverse sensory modalities to carry out tasks such as foraging, obstacle avoidance and social communication. While it is well known that many bat species use echolocation to find food and steer around obstacles, they also depend on other senses. For instance, some bats predominantly use vision to navigate, and others use olfaction to find food sources. In addition, bats rely on airflow sensors to stabilize their flight, primarily through signals carried by microscopic hairs embedded in their wings and tail membranes. Studies have shown that bats performing an obstacle avoidance task show changes in their flight behavior when dorsal wing hairs are removed. Additionally, electrophysiological studies have shown that wing hairs are involved in airflow sensing, but little is known about the contribution of sensory hairs on the ventral surfaces of the wing and tail membranes to their flight control and other complex behaviors, such as prey handling. Chapter 1 of my dissertation presents a general introduction to bat echolocation, flight kinematics, and airflow sensing for flight control. In Chapter 2, I review sensory hairs across the animal kingdom, from invertebrates to vertebrates. I discuss the role of sensory hairs for functions ranging from detection to locomotion and propose the use and benefit of mechanosensors in biologically-inspired technology. In Chapter 3, I devised an experiment to evaluate changes in capture success, as well changes in flight kinematics and adaptive sonar behavior, before and after depilation of sensory hairs in order to ascertain if these sensory hairs have a functional role in both airflow sensing for flight control and tactile sensing for prey handling. In Chapter 4, I designed an experiment aimed at determining if firing patterns of S1 neurons change with airflow speed and angle of attack and if wing hair depilation affects S1 responses to whole wing stimulation. To answer these questions, I record neural activity in S1 of sedated big brown bats while the entire contralateral wing is systematically exposed to naturalistic airflow in a wind tunnel. Finally, in Chapter 5, I address open questions that remain, present experiments aimed at filling these gaps, and consider key points important for future work

Innervation Patterns of Harp Seal (Pagophilus groenlandicus) Vibrissal Sensory Systems

Vibrissae, or whiskers, are largest among pinnipeds and are specialized hairs that potentially evolved to serve sensory, thermoregulatory or protective functions. Behavioral data from pinniped and rodent vibrissa studies indicate that functional differences exist between medial microvibrissae and lateral macrovibrissae. However, comparative data are lacking, and current pinniped studies only focus on the largest ventrolateral macrovibrissae. Consequently, we investigated the medial-to-lateral innervation and microanatomy of harp seal (Pagophilus groenlandicus) vibrissal Follicle-Sinus Complexes (F-SCs). F-SCs were sectioned either longitudinally or in cross-section. Sections remained unstained or were stained with a modified Bodian silver stain (innervation) or Masson’s trichrome stain (microanatomy). Harp seals possessed 88-105 F-SCs and each exhibited a tripartite blood organization system. Hair shafts were more circular medially but became more elliptical laterally. Medial F-SCs had more symmetrical dermal capsule thicknesses and distributions of major branches of the deep vibrissal nerve, but these symmetries diminished as F-SCs became more lateral. Medial-to-lateral axon counts ranged from 550 ± 97.4 axons/F-SC (medial) to 1632 ± 173.2 axons/F-SC (lateral). Overall, axon counts averaged 1221 ± 422.3 axons/F-SC (n=146 cross-sections), indicating a total of 117,235 axons/snout. Lateral F-SCs alone possessed a mean of 1533 ± 192.9 axons (n=82 cross-sections), which is similar to counts reported in other pinniped vibrissal innervation studies. These data suggest that conventional studies that only examine lateral vibrissae overestimate total innervation by ~20%. Moreover, we counted axon bundles with and without silver staining (n=834) and determined that unstained sections yielded more accurate and ~10% greater axon counts. Consequently, conventional analyses are likely only overestimating innervation by ~10% overall. The relationship between axon count and F-SC surface area was non-linear (p<<0.01; n=24 cross-sections), presumably from mechanoreceptors reaching carrying capacity, and axon densities were consistent across the snout. Presumptive Merkel-Neurite complexes and lanceolate endings were observed at the glassy membrane and outer root sheath interface. Our data agree well with behavioral research on pinnipeds and rodents that documents functional compartmentalization between micro-(medial) and macrovibrissae (lateral). Furthermore, our results support that vibrissal innervation variation observed among extant mammals initially diverged as a result of phylogeny and then environment (i.e., terrestrial, semi-aquatic, fully aquatic)

Innervation Patterns of Mystacial Vibrissae Support Active Touch Behaviors in California Sea Lions (Zalophus californianus)

Vibrissae, or whiskers, are highly developed sensory structures found in mammals. The follicles are referred to as Follicle Sinus Complexes (F-SC) due to the blood-filled sinuses. F-SCs are highly innervated compared to pelage. The most wellknown group of vibrissae, mystacial vibrissae, are found around the muzzle in mammals. Pinnipeds have the largest and most innervated vibrissae of any mammal. More aquatic mammals tend to have larger F-SCs and greater innervation investment (axons per FSC). Behavioral performance studies have shown that California sea lions Zalophus californianus (CSL, an otariid) excel at haptics whereas harbor seals Phoca vitulina (a phocid) excel at hydrodynamic trail following. The data presented in this thesis will infer vibrissal function from these studies. To date there has been no thorough investigation of innervation investment in an otariid. The objectives of this study were to investigate the innervation of the largest F-SCs, compare the innervation and microstructure to the most medial F-SCs, and compare the dorsal to ventral F-SCs. Follicles were dissected from tissues obtained from stranding programs and processed for histology. Axons were counted from wet mounted cross-sections. Asymmetry of axon bundles was present in all F-SC cross sections and have not been described before as well as blood vessels seen entering the DC of the LCS. There was a mean of 75±5 F-SCs per face muzzle. Innervation increased from medial (705 ±125 axons/F-SC) to lateral (1447±154) as well as from dorsal (541 ± 60) to the ventral F-SCs (1493 ± 327). Lateral F-SCs axon counts were similar to those in other pinniped studies. The total innervation from lateral axon counts (108,525 axons) agree with other studies but total innervation from all six areas (86,042 axons) was 20% less than values from only lateral F-SCs. Axon density of medial F-SCs were significantly more than lateral F-SCs. This finding is congruent with CSL behavioral performance data that suggest they excel at haptic touch. We found no substantial evidence to differentiate which F-SCs fall into micro- or microvibrissae categories. To date no study has investigated the dorsal-ventral micro anatomical and innervation patterns in any pinniped

Active touch sensing in pinnipeds

Active touch sensing in humans is characterised by making purposive movements with their fingertips. These movements are task-specific to maximise the relevant information gathered from an object. In whisker-touch sensing, previous research has suggested that whisker movements are purposive, but no one has ever examined task-specific whisker movements in any animal. Pinnipeds are whisker specialists, with long, mobile, sensitive whiskers and diverse whisker morphologies. The aim of this PhD is to investigate active touch sensing in Pinnipeds (seals, sea lions and walrus), by: i) describing whisker morphology; ii) comparing and quantifying whisker movements; and iii) characterising task-dependency of whisker movements during texture, size and luminance discrimination tasks. Pinnipeds with long, numerous whiskers, such as California sea lions (Zalophus californianus) and Stellar sea lions (Eumetopias jubatus) have larger infraorbital foramen (IOF) sizes and therefore, more sensitive whiskers. The IOF being a small hole in the skull, allowing the infraorbital nerve (ION) to pass through, which supplies sensation to the whiskers. Comparing whisker movements in Harbor seals (Phoca vitulina), California sea lions and Pacific walrus (Odobenidae rosmarus), showed these species all protracted their whiskers forwards and oriented their head towards a moving fish stimulus. However, California sea lions moved their whiskers more than the other species, and independently of the head. Due to the movement capabilities and sensitivity of whiskers in California sea lions, this species was used to investigate whether whiskers can be moved in a task-specific way. Results suggested that California sea lions make task-specific movements, by feeling around the edge of different-sized shapes, and focussing and spreading their whiskers on the centre of different-textured shapes. Therefore, California sea lion whiskers are controlled like a true active touch sensory system, similar to human fingertips. I suggest that active touch sensing is likely to efficiently guide foraging and prey capture in dark, murky waters in these animals. Moreover, the complexity of California sea lion whisker movements and their subsequent behaviours makes them a good candidate from which to further investigate animal decision-making, perception and cognition

Innervation patterns of sea otter (Enhydra lutris) mystacial follicle-sinus complexes

Sea otters (Enhydra lutris) are the most recent group of mammals to return to the sea, and may exemplify divergent somatosensory tactile systems among mammals. Therefore, we quantified the mystacial vibrissal array of sea otters and histologically processed follicle-sinus complexes (F - SCs) to test the hypotheses that the number of myelinated axons per F - SC is greater than that found for terrestrial mammalian vibrissae and that their organization and microstructure converge with those of pinniped vibrissae. A mean of 120.5 vibrissae were arranged rostrally on a broad, blunt muzzle in 7–8 rows and 9–13 columns. The F-SCs of sea otters are tripartite in their organization and similar in microstructure to pinnipeds rather than terrestrial species. Each F-SC was innervated by a mean 1339 ± 408.3 axons. Innervation to the entire mystacial vibrissal array was estimated at 161,313 axons. Our data support the hypothesis that the disproportionate expansion of the coronal gyrus in somatosensory cortex of sea otters is related to the high innervation investment of the mystacial vibrissal array, and that quantifying innervation investment is a good proxy for tactile sensitivity. We predict that the tactile performance of sea otter mystacial vibrissae is comparable to that of harbor seals, sea lions and walruses