Research Interests:
Research Interests:
Understanding how aquatic animals select and partition resources provides relevant information about community dynamics that can be used to help manage conservation efforts. The critically endangered hawksbill sea turtle (Eretmochelys... more
Understanding how aquatic animals select and partition resources provides relevant information about community dynamics that can be used to help manage conservation efforts. The critically endangered hawksbill sea turtle (Eretmochelys imbricata) spends an extended part of its juvenile development in coastal waters. A strong proclivity to remain resident in small areas, often in high density, raises questions about how juveniles partition resources including selection of habitat and spatial overlap among conspecifics. Using between 36 and 41 acoustic receivers in the 1.5 km2 study site, this study quantified day-and-night habitat selection, as well as 2D and 3D space use of 23 juvenile hawksbills within two adjacent Caribbean foraging grounds—Brewers Bay and Hawksbill Cove, St. Thomas, US Virgin Islands—between 2015 and 2018. We found that coral reef, rock, and the artificial dolosse forming an airport runway, were the most strongly selected habitats based on resource selection indic...
Research Interests:
Space-use by aquatic ectotherms is closely linked to environmental factors such as temperature due to thermal-mediated metabolism and energy requirements. These factors are important, as they may alter an animal’s exposure to... more
Space-use by aquatic ectotherms is closely linked to environmental factors such as temperature due to thermal-mediated metabolism and energy requirements. These factors are important, as they may alter an animal’s exposure to food/predators, hinder physiological function, increase competitive interactions, or even prompt population or biodiversity loss. Using general linear mixed-effects models, we investigated the influence of medium-term (months-years) environmental (diel period, water temperature, season, wind speed, air pressure, habitat type) and biological (turtle size) variation on space-use metrics for the Critically Endangered hawksbill sea turtleEretmochelys imbricata, including dive duration, activity space, and rate of movement. We tracked 17 resident juveniles between August 2015 and May 2018 with a compact acoustic telemetry array (35-41 receivers in ~1 km2) in Brewers Bay, US Virgin Islands. Diel differences in space-use were significant and highlighted periods of rel...
Research Interests:
Extreme weather events (e.g., cyclones, floods, droughts) are capable of changing ecosystems and altering how animals obtain resources. Understanding the behavioural responses of animals being impacted by these natural events can help... more
Extreme weather events (e.g., cyclones, floods, droughts) are capable of changing ecosystems and altering how animals obtain resources. Understanding the behavioural responses of animals being impacted by these natural events can help initiate and ameliorate conservation or management programs. This study investigated short- and long-term space-use of the critically endangered hawksbill sea turtle (Eretmochelys imbricata), as well as five species of fishes and stingrays, in response to two of the most destructive Caribbean hurricanes in known history – Irma and Maria, which were at their peak intensity when they passed the US Virgin Islands in September of 2017. Using passive acoustic telemetry in St. Thomas, US Virgin Islands, we show a variety of short-term behavioural patterns initiated across species to reduce exposure to the strong environmental conditions, such as moving to deeper habitats within the study area. Although short-term expansion of activity space was evident for s...
Research Interests:
Research Interests:
Splenic volume was measured by computerized axial tomography in three harbor seals (Phoca vitulina) and two California sea lions (Zalophus californianus). Volumes ranged from 228 to 679 ml, representing 0.8-3.0% of calculated percentage... more
Splenic volume was measured by computerized axial tomography in three harbor seals (Phoca vitulina) and two California sea lions (Zalophus californianus). Volumes ranged from 228 to 679 ml, representing 0.8-3.0% of calculated percentage body mass. Despite possible variation in the state of splenic contraction during the examination, these values are in the upper range of reported mammalian splenic volumes (as % of body mass). This reinforces the pinniped splenic erythrocyte storage concept.
Research Interests:
The use of near infra-red spectroscopy to monitor the oxygenation state of tissue in vivo with surface mounted probes has been reported (1). However selective monitoring of tissue located deep in the body has required surgery to isolate... more
The use of near infra-red spectroscopy to monitor the oxygenation state of tissue in vivo with surface mounted probes has been reported (1). However selective monitoring of tissue located deep in the body has required surgery to isolate the tissue and position probes on the tissue surface. To eliminate this requirement a catheter-like fiber optic probe was developed to monitor deep muscle oxygenation.
Research Interests:
Near Infra Red (NIR) spectroscopy can be applied non-invasively to organs and tissues in vivo. Spectra can be taken through organs as thick as the human head for identification of the absorbing components (1). And it is possible to... more
Near Infra Red (NIR) spectroscopy can be applied non-invasively to organs and tissues in vivo. Spectra can be taken through organs as thick as the human head for identification of the absorbing components (1). And it is possible to monitor the reactions of the absorbing molecules to physiological manipulations with a multi-wavelength, differential spectrophotometer designed for the purpose, as was shown for the first time at the 1984 ISOTT meeting (2). The primary variable is oxygen delivery to the tissue or organ and the instrument has therefore been called the NIR Oxygen Sufficiency Monitor or NIROSCOPE (c.f. 3 for a brief review).
Research Interests:
This communication presents our recent modeling and experimental study on the relationship between oxygen consumption rate and delivery rate. Oxygen consumption rate \((\dot{\text{V}}\text{o}_{2})\) by an organ is regarded to represent... more
This communication presents our recent modeling and experimental study on the relationship between oxygen consumption rate and delivery rate. Oxygen consumption rate \((\dot{\text{V}}\text{o}_{2})\) by an organ is regarded to represent its tissue O2 metabolic rate. Under steady state, \((\dot{\text{V}}\text{o}_{2})\) is usually determined from the product of blood flow rate and the arteriovenous O2 concentration difference across the organ. Oxygen delivery rate \((\dot{\text{D}}\text{o}_{2})\) is defined as the product of arterial O2 concentration and blood flow rate. Numerous investigations of the relationship between \((\dot{\text{D}}\text{o}_{2})\) and \((\dot{\text{V}}\text{o}_{2})\) have been reported. Many of these studies were related to the biphasic supply-dependent O2 consumption concept for tissue hypoxia determina-tion[1][2]. The biphasic concept states that, for a given energy demand by the tissue, a plot of \((\dot{\text{V}}\text{o}_{2})\) versus \((\dot{\text{D}}\text{o}_{2})\) displays two distinct regions (or phases). In one region, \((\dot{\text{V}}\text{o}_{2})\) remains constant regardless of changes in \((\dot{\text{D}}\text{o}_{2})\). When \((\dot{\text{D}}\text{o}_{2})\) declines below a threshold value (the “critical \((\dot{\text{D}}\text{o}_{2})\)”), \((\dot{\text{V}}\text{o}_{2})\) becomes an approximately linear function of \((\dot{\text{D}}\text{o}_{2})\).
Research Interests:
Research Interests:
Research Interests:
Research Interests: Fluorescence Microscopy, Biology, Mitochondria, Biophysical Chemistry, Medicine, and 13 moreBiological Sciences, Mice, Animals, Feasibility Studies, Physical sciences, Fluorescence Imaging, CHEMICAL SCIENCES, High Resolution, Skeletal Muscle, Tissue distribution, Nicotinamide adenine dinucleotide, Muscle fibers skeletal, and nadp
Much attention has been focused on the passive mechanical properties of the myocardium, which determines left ventricular (LV) diastolic mechanics, but the significance of the visceral pericardium (VP) has not been extensively studied. A... more
Much attention has been focused on the passive mechanical properties of the myocardium, which determines left ventricular (LV) diastolic mechanics, but the significance of the visceral pericardium (VP) has not been extensively studied. A unique en face three-dimensional volumetric view of the porcine VP was obtained using two-photon excitation fluorescence to detect elastin and backscattered second harmonic generation to detect collagen, in addition to standard light microscopy with histological staining. Below a layer of mesothelial cells, collagen and elastin fibers, extending several millimeters, form several distinct layers. The configuration of the collagen and elastin layers as well as the location of the VP at the epicardium providing a geometric advantage led to the hypothesis that VP mechanical properties play a role in the residual stress and passive stiffness of the heart. The removal of the VP by blunt dissection from porcine LV slices changed the opening angle from 53.3...
Research Interests: Physiology, Fluorescence Microscopy, Medicine, Elasticity, Collagen, and 15 moreFemale, Animals, Male, Three Dimensional Imaging, American, Dissection, Medical Physiology, Elastin, Mechanical Stress, Pericardium, Sus Scrofa, Left Ventricle, Mechanical Property, ventricular pressure, and Ventricular Function
SUMMARY In several pinniped species, the heart rates observed during unrestrained dives are frequently higher than the severe bradycardias recorded during forced submersions. To examine other physiological components of the classic ‘dive... more
SUMMARY In several pinniped species, the heart rates observed during unrestrained dives are frequently higher than the severe bradycardias recorded during forced submersions. To examine other physiological components of the classic ‘dive response’ during such moderate bradycardias, a training protocol was developed to habituate harbor seals (Phoca vitulina) to short forced submersions. Significant changes were observed between physiological measurements made during naive and trained submersions (3–3.5 min). Differences were found in measurements of heart rate during submersion (naive 18±4.3 beats min–1versus trained 35±3.4 beats min–1), muscle blood flow measured using laser-Doppler flowmetry (naive 1.8±0.8 ml min–1 100 g–1versus trained 5.8±3.9 ml min–1 100 g–1), change in venous PO2 (naive –0.44±1.25 kPa versus trained –1.48±0.76 kPa) and muscle deoxygenation rate (naive –0.67±0.27 mvd s–1versus trained –0.51±0.18 mvd s–1, a relative measure of muscle oxygenation provided by the V...
Research Interests:
Near infrared spectroscopy (NIRS) can monitor both the redox status of Cytochrome c oxidase located in the mitochondria within the cell and the oxygenation of the blood in the tissue being monitored. Since the enzyme catalyzes more than... more
Near infrared spectroscopy (NIRS) can monitor both the redox status of Cytochrome c oxidase located in the mitochondria within the cell and the oxygenation of the blood in the tissue being monitored. Since the enzyme catalyzes more than 90% of oxygen utilization, it is the sink for the oxygen while the hemoglobin in the capillaries is the oxygen source. In order to evaluate the oxidative metabolic status of a tissue the optical data obtained from both molecules are commonly interpreted on the basis of test tube experiments with purified preparations. We are concerned that the validity of this practice may not have been tested sufficiently and raise four basic questions that have not yet been answered. Citing some examples of in vitro versus in vivo differences we conclude that more effort should be expended on the in vivo testing of the range of the signals, their natural variability, and the physiological and pathological meaning of their deviations from norm. © 1999 Society of Photo-Optical Instrumentation Engineers.