Sam Ridgway - Academia.edu (original) (raw)

Complete Set of Publications by Sam Ridgway

The evolutionary process of adaptation to an obligatory aquatic existence dramatically modified c... more The evolutionary process of adaptation to an obligatory aquatic existence dramatically modified cetacean brain structure and function. The brain of the killer whale (Orcinus orca) may be the largest of all taxa supporting a panoply of cognitive, sensory, and sensorimotor abilities. Despite this, examination of the O. orca brain has been limited in scope resulting in significant deficits in knowledge concerning its structure and function. The present study aims to describe the neural organization and potential function of the O. orca brain while linking these traits to potential evolutionary drivers. Magnetic resonance imaging was used for volumetric analysis and three-dimensional reconstruction of an in situ postmortem O. orca brain. Measurements were determined for cortical gray and cerebral white matter, subcortical nuclei, cerebellar gray and white matter, corpus callosum, hippocampi, superior and inferior colliculi, and neuroendocrine structures. With cerebral volume comprising 81.51 % of the total brain volume, this O. orca brain is one of the most corticalized mammalian brains studied to date. O. orca and other delphinoid cetaceans exhibit isometric scaling of cerebral white matter with increasing brain size, a trait that violates an otherwise evolutionarily conserved cerebral scaling law. Using comparative neurobiology, it is argued that the divergent cerebral morphology of delphinoid cetaceans compared to other mammalian taxa may have evolved in response to the sensorimotor demands of the aquatic environment. Furthermore, selective pressures associated with the evolution of echolocation and unihemispheric sleep are implicated in substructure morphology and function. This neuroanatomical dataset, heretofore absent from the literature, provides important quantitative data to test hypotheses regarding brain structure, function, and evolution within Cetacea and across Mammalia.

We want to report an erroneous value that has spread through the literature about the brain of th... more We want to report an erroneous value that has spread through the literature about the brain of the blue whale, Balaenoptera musculus. The blue whale is the largest cetacean and the largest animal on earth. Established methods confirm a maximum body length of 30 m and a maximum body mass approaching 200,000 kg (Ash 1952. While there are methods that confirm these two body measures, data on the brain of the largest animal on earth are sparse. This is partly due to the difficulties associated with extracting and measuring such large brains. From sharks to primates, there is an increase in behavioral complexity with an increase in brain size (Clutton-Brock and Harvey 1980, Northcutt 2002).

nally to Balaenidae. We also found the same general trend when we compared brain volume relative ... more nally to Balaenidae. We also found the same general trend when we compared brain volume relative to body length, except that the Delphinidae and Phocoenidae-Monodonti-dae groups do not differ significantly. The Balaenidae have the smallest relative brain mass and the lowest cerebral cortex surface area. Brain parts also vary. Relative to body mass and to body length, dolphins also have the largest cerebel-lums. Cortex surface area is isometric with brain size when we exclude the Balaenidae. Our data show that the brains of Balaenidae are less convoluted than those of the other cetaceans measured. Large vascular networks inside the cranial vault may help to maintain brain temperature, and these nonbrain tissues increase in volume with body mass and with body length ranging from 8 to 65% of the endocranial volume. Because endocranial vascular networks and other adnexa, such as the tentorium cerebelli, vary so much in different species, brain size measures from endocasts of some extinct cetaceans may be overestimates. Our regression of body length on endocranial adnexa might be used for better estimates of brain volume from endocasts or from endocra-nial volume of living species or extinct cetaceans. Keywords Dolphins · Whales · Cetacean · Brain size · Cerebellum · Brain · Cortex Abstract We compared mature dolphins with 4 other groupings of mature cetaceans. With a large data set, we found great brain diversity among 5 different taxonomic groupings. The dolphins in our data set ranged in body mass from about 40 to 6,750 kg and in brain mass from 0.4 to 9.3 kg. Dolphin body length ranged from 1.3 to 7.6 m. In our combined data set from the 4 other groups of cetaceans, body mass ranged from about 20 to 120,000 kg and brain mass from about 0.2 to 9.2 kg, while body length varied from 1.21 to 26.8 m. Not all cetaceans have large brains relative to their body size. A few dolphins near human body size have human-sized brains. On the other hand, the absolute brain mass of some other cetaceans is only one-sixth as large. We found that brain volume relative to body mass decreases from Del-phinidae to a group of Phocoenidae and Monodontidae, to a group of other odontocetes, to Balaenopteroidea, and fi

principle of physics. The abundance of eye types in nature continues to inspire counterparts in o... more principle of physics. The abundance of eye types in nature continues to inspire counterparts in optics. For example, the mirror-based optical system of the compound eyes of shrimps and lobsters have recently found use as the optical basis for wide-angle x-ray lenses to explore space. 8

eScholarship provides open access, scholarly publishing services to the University of California ... more eScholarship provides open access, scholarly publishing services to the University of California and delivers a dynamic research platform to scholars worldwide.

Similar to humans, bottlenose dolphins (Tursiops truncatus) can develop metabolic syndrome and as... more Similar to humans, bottlenose dolphins (Tursiops truncatus) can develop metabolic syndrome and associated high ferritin. While fish and fish-based fatty acids may protect against metabolic syndrome in humans, findings have been inconsistent. To assess potential protective factors against metabolic syndrome related to fish diets, fatty acids were compared between two dolphin populations with higher (n = 30, Group A) and lower (n = 19, Group B) mean insulin (11 ± 12 and 2 ± 5 μIU/ml, respectively; P < 0.0001) and their dietary fish. In addition to higher insulin, triglycerides, and ferritin, Group A had lower percent serum heptadecanoic acid (C17:0) compared to Group B (0.3 ± 0.1 and 1.3 ± 0.4%, respectively; P < 0.0001). Using multivariate stepwise regression, higher percent serum C17:0, a saturated fat found in dairy fat, rye, and some fish, was an independent predictor of lower insulin in dolphins. Capelin, a common dietary fish for Group A, had no detectable C17:0, while pinfish and mullet, common in Group B's diet, had C17:0 (41 and 67 mg/100g, respectively). When a modified diet adding 25% pinfish and/or mullet was fed to six Group A dolphins over 24 weeks (increasing the average daily dietary C17:0 intake from 400 to 1700 mg), C17:0 serum levels increased, high ferritin decreased, and blood-based metabolic syndrome indices normalized toward reference levels. These effects were not found in four reference dolphins. Further, higher total serum C17:0 was an independent and linear predictor of lower ferritin in dolphins in Group B dolphins. Among off the shelf dairy products tested, butter had the highest C17:0 (423mg/100g); nonfat dairy products had no detectable C17:0. We hypothesize that humans' movement away from diets with potentially beneficial saturated fatty acid C17:0, including whole fat dairy products, could be a contributor to widespread low C17:0 levels, higher ferritin, and metabolic syndrome.

AQUATIC ANIMALS T he US Navy MMP has housed and cared for bottlenose dolphins (Tursiops truncatus... more AQUATIC ANIMALS T he US Navy MMP has housed and cared for bottlenose dolphins (Tursiops truncatus) for over 50 years. Because of the clinical and biological research conducted over the past half century, knowledge of dolphin physiology, clinical medicine, and behavior at the MMP has expanded greatly. 1-7 Specifically, clinical research has advanced dolphin medicine in areas such as diagnostic imaging, infectious and metabolic disease discovery and health assessments, and the establishment of reference ranges for blood-based indicators of health and immune status. This research has improved the scientific community' s general understanding of dolphin physiology Objective-To evaluate annual survival and mortality rates and the longevity of a managed population of bottlenose dolphins (Tursiops truncatus). Design-Retrospective cohort study. Animals-103 bottlenose dolphins at the US Navy Marine Mammal Program (MMP). Procedures-Population age structures, annual survival and crude mortality rates, and median age at death for dolphins > 30 days old were determined from 2004 through 2013. Results-During 2004 through 2013, the annual survival rates for MMP dolphins ranged from 0.98 to 1.0, and the annual crude mortality rates ranged from 0% to 5%, with a mean of 2.7%. The median age at death was 30.1 years from 2004 through 2008 and increased to 32 years from 2009 through 2013. The maximum age for a dolphin in the study was 52 years. Conclusions and Clinical Relevance-Results indicated that the annual mortality rates were low and survival rates were high for dolphins in the MMP from 2004 through 2013 and that the median age at death for MMP dolphins during that time was over 10 years greater than that reported in free-ranging dolphins. These findings were likely attributable to the continually improving care and husbandry of managed dolphin populations. (J Am Vet Med Assoc 2015;246:893-898)

Dolphins fishing alone in open waters may whistle without interrupting their sonar clicks as they... more Dolphins fishing alone in open waters may whistle without interrupting their sonar clicks as they find and eat or reject fish. Our study is the first to match sound and video from the dolphin with sound and video from near the fish. During search and capture of fish, free-swimming dolphins carried cameras to record video and sound. A hydrophone in the far field near the fish also recorded sound. From these two perspectives, we studied the time course of dolphin sound production during fish capture. Our observations identify the instant of fish capture. There are three consistent acoustic phases: sonar clicks locate the fish; about 0.4 s before capture, the dolphin clicks become more rapid to form a second phase, the terminal buzz; at or just before capture, the buzz turns to an emotional squeal (the victory squeal), which may last 0.2 to 20 s after capture. The squeals are pulse bursts that vary in duration, peak frequency and amplitude. The victory squeal may be a reflection of emotion triggered by brain dopamine release. It may also affect prey to ease capture and/or it may be a way to communicate the presence of food to other dolphins. Dolphins also use whistles as communication or social sounds. Whistling during sonar clicking suggests that dolphins may be adept at doing two things at once. We know that dolphin brain hemispheres may sleep independently. Our results suggest that the two dolphin brain hemispheres may also act independently in communication.

animals. Here we show that the large cerebellar difference likely relates to evolutionary history... more animals. Here we show that the large cerebellar difference likely relates to evolutionary history, diving, sensory capability, and ecology.

For many years, we heard sounds associated with reward from dolphins and belugas. We named these ... more For many years, we heard sounds associated with reward from dolphins and belugas. We named these pulsed sounds victory squeals (VS), as they remind us of a child's squeal of delight. Here we put these sounds in context with natural and learned behavior. Like bats, echolocating cetaceans produce feeding buzzes as they approach and catch prey. Unlike bats, cetaceans continue their feeding buzzes after prey capture and the after portion is what we call the VS. Prior to training (or conditioning), the VS comes after the fish reward; with repeated trials it moves to before the reward. During training, we use a whistle or other sound to signal a correct response by the animal. This sound signal, named a secondary reinforcer (SR), leads to the primary reinforcer, fish. Trainers usually name their whistle or other SR a bridge, as it bridges the time gap between the correct response and reward delivery. During learning, the SR becomes associated with reward and the VS comes after the SR rather than after the fish. By following the SR, the VS confirms that the animal expects a reward. Results of early brain stimulation work suggest to us that SR stimulates brain dopamine release, which leads to the VS. Although there are no direct studies of dopamine release in cetaceans, we found that the timing of our VS is consistent with a response after dopamine release. We compared trained vocal responses to auditory stimuli with VS responses to SR sounds. Auditory stimuli that did not signal reward resulted in faster responses by a mean of 151 ms for dolphins and 250 ms for belugas. In laboratory animals, there is a 100 to 200 ms delay for dopamine release. VS delay in our animals is similar and consistent with vocalization after dopamine release. Our novel observation suggests that the dopamine reward system is active in cetacean brains.

The present study documents the morphology of neurons in several regions of the neocortex from th... more The present study documents the morphology of neurons in several regions of the neocortex from the bottlenose dolphin (Tursiops truncatus), the North Atlantic minke whale (Balaenoptera acutorostrata), and the humpback whale (Megaptera novaeangliae). Golgi-stained neurons (n = 210) were analyzed in the frontal and temporal neocortex as well as in the primary visual and primary motor areas. Qualitatively, all three species exhibited a diversity of neuronal morphologies, with spiny neurons including typical pyramidal types, similar to those observed in primates and rodents, as well as other spiny neuron types that had more variable morphology and/or orientation. Five neuron types, with a vertical apical dendrite, approximated the general pyramidal neuron morphology (i.e., typical pyramidal, extraverted, magnopyramidal, multiapical, and bitufted neurons), with a predominance of typical and extraverted pyramidal neurons. In what may represent a cetacean morphological apomorphy, both typical pyramidal and magnopyramidal neurons frequently exhibited a tri-tufted variant. In the humpback whale, there were also large, star-like neurons with no discernable apical dendrite. Aspiny bipolar and multipolar interneurons were morphologically consistent with those reported previously in other mammals. Quantitative analyses showed that neuronal size and dendritic extent increased in association with body size and brain mass (bottlenose dolphin \ minke whale \ humpback whale). The present data thus suggest that certain spiny neuron morphologies may be apomorphies in the neocortex of cetaceans as compared to other mammals and that neuronal dendritic extent covaries with brain and body size.

Breath analysis, including measurement of nitric oxide (NO), is a noninvasive diagnostic tool tha... more Breath analysis, including measurement of nitric oxide (NO), is a noninvasive diagnostic tool that may help evaluate cetacean health. This is the first report on the effects of breath hold duration, feeding, and lung disease on NO in dolphin exhaled breath. Three healthy dolphins were trained to hold their breath for 30, 60, 90, and 120 s and then exhale into an underwater funnel. Exhaled NO values from 157 breath samples were compared among three healthy dolphins by breath hold time and after fasting and feeding. Exhaled NO values were also measured in two dolphins with pulmonary disease. NO in dolphin breath was higher compared to ambient air; healthy dolphins had higher NO concentrations in their breath after feeding compared to after overnight fasting; and there were no significant differences in exhaled NO levels by breath hold duration. A dolphin with Mycoplasma-associated pneumonia and chronic gastrointestinal disease had higher postprandial exhaled NO levels compared to healthy controls. This study demonstrates, contrary to previous publications, that dolphins exhale NO. Given the high standard deviations present in exhaled breath NO values, future studies are needed to further standardize collection methods or identify more reliable samples (e.g., blood).

In the 1960s, I explored some aspects of carbohydrate metabolism in healthy bottlenose dolphins (... more In the 1960s, I explored some aspects of carbohydrate metabolism in healthy bottlenose dolphins (Tursiops truncatus). Their physiological picture resembled what had been described for hyperthyroid diabetics. Dolphins have elevated thyroid hormone turnover, and fasting dolphins maintain a relatively high level of plasma glucose. After dolphins ingest glucose, plasma levels remain high for many hours. Interestingly, plasma glucose must exceed 300 mg/dL (about twice as high as the human threshold) before glucose appears in urine. Due to their diabetes-like states, trainability, and unique natural respiratory anatomy and physiology, dolphins may offer useful clues to metabolites in the breath that may be used to non-invasively monitor diabetes in humans. Dolphins take very rapid and deep breaths that are four or five times as deep as humans and other terrestrial mammals, making them ideal for physiological assessment using non-invasive exhaled air. Avenues for successfully identifying breath-based markers for metabolic disease and physiology in dolphins can be done with both modern technology and the evolutionarily advantageous canine nose. This review summarizes aspects of dolphin metabolism previously learned and offers new directions for diabetes research that may benefit both dolphin and human health.

Neuroanatomical research into the brain of the bottlenose dolphin (Tursiops truncatus) has reveal... more Neuroanatomical research into the brain of the bottlenose dolphin (Tursiops truncatus) has revealed striking similarities with the human brain in terms of size and complexity. However, the dolphin brain also contains unique allometric relationships. When compared to the human brain, the dolphin cerebellum is noticeably larger. Upon closer examination, the lobule composition of the cerebellum is distinct between the two species. In this study, we used magnetic resonance imaging to analyze cerebellar anatomy in the bottlenose dolphin and measure the volume of the separate cerebellar lobules in the bottlenose dolphin and human. Lobule identification was assisted by three-dimensional modeling. We find that lobules VI, VIIb, VIII, and IX are the largest lobules of the bottlenose dolphin cerebellum, while the anterior lobe (I-V), crus I, crus II, and the flocculonodular lobe are smaller. Different lobule sizes may have functional implications. Auditoryassociated lobules VIIb, VIII, IX are likely large in the bottlenose dolphin due to echolocation abilities. Our study provides quantitative information on cerebellar anatomy that substantiates previous reports based on gross observation and subjective analysis. This study is part of a continuing effort toward providing explicit descriptions of cetacean neuroanatomy to support the interpretation of behavioral studies on cetacean cognition. Anat Rec, 296:1215-1228,

Bottlenose dolphins (Tursiops truncatus) wore opaque suction cups over their eyes while stationin... more Bottlenose dolphins (Tursiops truncatus) wore opaque suction cups over their eyes while stationing
behind an acoustically opaque door. This put the dolphins in a known position and orientation.
When the door opened, the dolphin clicked to detect targets. Trainers specified that Dolphin S emit
a whistle if the target was a 7.5 cm water filled sphere, or a pulse burst if the target was a rock. S
remained quiet if there was no target. Dolphin B whistled for the sphere. She remained quiet for
rock and for no target. Thus, S had to choose between three different responses, whistle, pulse burst,
or remain quiet. B had to choose between two different responses, whistle or remain quiet. S gave
correct vocal responses averaging 114 ms after her last echolocation click (range 182 ms before and
219 ms after the last click). Average response for B was 21 ms before her last echolocation click
(range 250 ms before and 95 ms after the last click in the train). More often than not, B began her
whistle response before her echolocation train ended. The findings suggest separate neural pathways
for generation of response vocalizations as opposed to echolocation clicks.
VC 2012 Acoustical Society of America. [DOI: 10.1121/1.3664074]
PACS number(s): 43.80.Lb, 43.80.Ka, 43.64.Tk [JAS] Pages: 593–598
I. INTRODUCTION
Speed of information processing in the brain is probably
quite important in echolocation. Dolphins often pursue fast
swimming prey in the ocean, an environment that may contain
numerous prey and non-prey items that must be identified.
Fast and accurate decisions will contribute to the
success of the individual.
Echolocating dolphins emit trains of clicks to detect a
target. In studies of echolocating dolphins, each following
click in the train is often not produced until about 20 ms after
reception of the target echo from the preceding click. Thus,
bottlenose dolphins appear able to time echolocation clicks
so that succeeding clicks are produced about 20 ms over the
round-trip travel time of the click from the animal to the target
(Morozov et al., 1972; Au et al., 1974; Kadane and
Penner, 1983;

In dolphins, natural selection has developed unihemispheric sleep where alternating hemispheres o... more In dolphins, natural selection has developed unihemispheric sleep where alternating hemispheres of their brain stay awake. This allows dolphins to maintain consciousness in response to respiratory demands of the ocean. Unihemispheric sleep may also allow dolphins to maintain vigilant states over long periods of time. Because of the relatively poor visibility in the ocean, dolphins use echolocation to interrogate their environment. During echolocation, dolphin produce clicks and listen to returning echoes to determine the location and identity of objects. The extent to which individual dolphins are able to maintain continuous vigilance through this active sense is unknown. Here we show that dolphins may continuously echolocate and accurately report the presence of targets for at least 15 days without interruption. During a total of three sessions, each lasting five days, two dolphins maintained echolocation behaviors while successfully detecting and reporting targets. Overall performance was between 75 to 86% correct for one dolphin and 97 to 99% correct for a second dolphin. Both animals demonstrated diel patterns in echolocation behavior. A 15-day testing session with one dolphin resulted in near perfect performance with no significant decrement over time. Our results demonstrate that dolphins can continuously monitor their environment and maintain long-term vigilant behavior through echolocation. Citation: Branstetter BK, Finneran JJ, Fletcher EA, Weisman BC, Ridgway SH (2012) Dolphins Can Maintain Vigilant Behavior through Echolocation for 15 Days without Interruption or Cognitive Impairment. PLoS ONE 7(10): e47478.