Vertical auditory acuity of the bottlenose dolphin

The accuracy in locating underwater sounds in the vertical median plane was determined for the Black Sea bottlenose dolphin Tursiops truncatus trained by operant conditioning with food reinforcement. The minimal perceived angles for 1-s tone signals were 2.5° at 5 or 20 kHz and 2.0° at 120 kHz; for 1-s trains of clicks centered at 120 kHz the acuity was still better, ～1.5°. Dolphins may locate different sounds using different yet equally efficient mechanisms, and they are the best in analyzing the acoustic space among marine mammals studied.     

Quantification of ECoG stages of sleep in the bottlenose dolphin

Single-hemisphere low-wave sleep was shown to be the dominant form of natural sleep according to quantitative analysis of duration of ECoG sleep phases. Combined variants of bilateral and unilateral ECoG synchronization total 33.4% of the 24-h cycle, of which unilateral slow-wave sleep accounts for 28.8%. Each of the bottlenose dolphin's two hemispheres remains in a state of slow-wave ECoG for an average of 19% of the cycle. The highest percentage duration of sleep occurred during the afternoon and nighttime. Overall duration of ECoG synchronization may differ in the two hemispheres but evens out in the dolphin over a number of 24-h cycles. Spells of single-hemisphere sleep tend to alternate between the two different hemispheres.A. N. Severtsov Institute of Evolutionary Morphology and Animal Ecology. Translated from Neirofiziologiya, Vol. 20, No. 4, pp. 532–538, July–August, 1988.     

Lymphangiomyomatosis in the Atlantic bottlenose dolphin (Tursiops truncatus).

The first case of lymphangiomyomatosis in a marine mammal is reported from a stranded male Atlantic bottlenose dolphin (Tursiops truncatus). This progressive proliferative disease involved the lungs and the mediastinal and probably mesenteric lymph nodes. An extraordinarily low level of testosterone may have been pathologically significant since all reported cases of this disease in humans occur in females.     

Efficiency of body conduction of underwater sounds in the bottlenose dolphin

Hearing thresholds of the Black Sea bottlenose dolphin Tursiops truncatus for tonal and composite underwater sounds within 50 kHz were ascertained in fully or partly submerged (head out of water) animals (trained by operant conditioning with food reinforcement). Perception of sounds conducted through the body deteriorated in all cases (thresholds for 75%-correct response rose typically by 6-24 dB); the least changes were observed for 10 and 20 kHz tones. The aggregate data also suggested significant individual variations.     

Characterization of beam patterns of bottlenose dolphin in the transversal plane

The characteristics of the absolute auditory sensitivity of the bottlenose dolphin (Tursiops truncatus p.) in the transverse plane have been measured using short broad-band stimuli simulating dolphin clicks (with energy maximum at frequencies 8, 16, 30, 50 and 100 kHz). Experiments were performed using the method of conditioned reflexes with food reinforcement. It was shown that, in the frequency range of 8-30 kHz, the absolute sensitivity of dolphin hearing in any ventral and lateral directions of the transverse plane is only by 2-8 dB worse than in the nasal direction. Moreover, it is approximately by 25-30 dB better than at frequencies of 50-100 kHz. At frequencies of 8-30 kHz, a pronounced dorsoventral asymmetry has been observed. In this frequency range, it reaches approximately 15-18 dB whereas at frequencies of 50-100 kHz, this asymmetry decreases to 2-3 dB. In the dorsal direction, the auditory sensitivity is by 18 dB worse than in the nasal one at frequencies of around 8 kHz, and the difference rises smoothly to 33 dB at frequencies of about 100 kHz. At frequencies of 50-100 kHz, the acoustical thresholds of the cross-section plane in comparison with thresholds for the with nasal direction get worse almost uniformly in all directions by 25-33 dB. As a result, in the transversal plane, the beam patterns have a nearly circular form, unlike the patterns at frequencies of 8-30 kHz. The results are discussed in terms of the model of sound perception through the left and right mental foramens. The biological expediency of the asymmetry is emphasized.     

Characterization of beam patterns of bottlenose dolphin in the transverse plane

The characteristics of absolute auditory sensitivity of the bottlenose dolphin (Tursiops truncatus) in the transverse plane have been measured using short broadband stimuli simulating dolphin clicks (with energy maximum at frequencies 8, 16, 30, 50 and 100 kHz). Experiments were performed using the method of conditioned reflexes with food reinforcement. It is shown that, in the frequency range of 8–30 kHz, the absolute sensitivity of dolphin hearing in any ventral and lateral directions of the transverse plane is only 2–8 dB worse than in the rostral direction. Moreover, it is 25–30 dB better than at 50–100 kHz. At 8–30 kHz, pronounced dorsoventral asymmetry has been observed. In this frequency range, it reaches 15–18 dB whereas at 50–100 kHz this asymmetry decreases to 2–3 dB. In the dorsal direction, the auditory sensitivity is 18 dB worse than in the rostral one at ∼8 kHz, and the difference rises smoothly to 33 dB at ∼100 kHz. At 50–100 kHz, the acoustical thresholds in the transverse plane relative to those for the with rostral direction get worse almost uniformly in all directions by 25–33 dB. As a result, in the transverse plane the beam patterns are nearly circular, unlike those at 8–30 kHz. The results are discussed in terms of the model of sound perception through the left and right mental foramens. The biological relevance of such asymmetry is emphasized.     

Eight polymorphic microsatellite loci for bottlenose dolphin and other cetacean species

We developed eight polymorphic microsatellite loci that can be used to elucidate population structure and aid management of bottlenose dolphins, Tursiops truncatus, in the northwest Atlantic. These loci averaged nine alleles, with no evidence for null alleles. Their cross‐species utility was examined in Cephalorhynchus commersonii, Delphinus delphis, Delphinapterus leucas, Eschrictius robustus, Globicephala macrorhynchus, Lagenorhynchus obliquidens, Orcinus orca, Steno bredanensis and Stenella clymene. On average, 75% of the loci were polymorphic in these species (range = 50–88%). Our results indicate that these loci will be useful for elucidating population structure of bottlenose dolphin as well as of other cetacean species.     

Herpes simplex-like infection in a bottlenose dolphin stranded in the Canary Islands

A bottlenose dolphin, stranded in the Canary Islands in 2001 exhibited non-suppurative encephalitis. No molecular detection of cetacean morbillivirus (CeMV) was found, but a herpesviral-specific band of 250 bp was detected in the lung and brain. The sequenced herpesviral PCR product was compared with GenBank sequences, obtaining 98% homology (p-distance of 0.02) with Human herpesvirus 1 (herpes simplex virus 1 or HSV-1). This is the first report of a herpes simplex-like infection in a stranded dolphin.     

Behaviorally measured tactile sensitivity in the common bottlenose dolphin,Tursiops truncatus

Little research has been conducted on the somatosensory system of toothed whales and it remains uncertain how tactile sensitivity varies about their bodies. In this study, tactile sensitivity to high-frequency (250-Hz) displacement of the skin was quantified in three trained adult common bottlenose dolphins (Tursiops truncatus) using a vibratory device (tactor). The magnitude of skin displacement was controlled by varying the voltage to the tactor held against the skin surface with a constant force. Tactile thresholds were determined using an adaptive method of limits in which dolphins reported perception of the tactile stimulus by producing a whistle. Displacement thresholds ranged from 2.4 to 40 μm, with the greatest sensitivity found along the rostrum, melon, and blowhole. Sensitivity decreased caudally along the body, with the dorsal fin and tip of the fluke being the least sensitive locations tested. The results support hypotheses that the follicles on the dolphin rostrum are particularly important for perception. The reduction in tactile sensitivity at the appendages is consistent with their primary role in stabilization and locomotion compared to exploration or environmental sensing.     

Congenital toxoplasmosis in a Indo-Pacific bottlenose dolphin (Tursiops aduncus)

Toxoplasma gondii was identified in tissues of a stillborn late-term fetus from an Indo-Pacific bottlenose dolphin (Tursiops aduncus). Myocardial necrosis and nonsuppurative inflammation in the heart and nonsuppurative necrotizing encephalitis were associated with tachyzoites and tissue cysts. The diagnosis was confirmed by immunohistochemical staining with anti-T. gondii-specific polyclonal rabbit serum.     

Struvite calculus in the vagina of a bottlenose dolphin (Tursiops truncatus)

On 27 January 2000, a struvite calculus was observed in the vagina during necropsy of a 138-cm-long female bottlenose dolphin (Tursiops truncatus) collected from the Stono River, South Carolina (USA). Vaginal calculi have been reported in other species of cetaceans but not in bottlenose dolphins. Urinary tract infection might have been an underlying cause of the calculus. While urinary tract inflammation was not detected by light microscopic evaluation of sections of the urinary tract, it is conceivable that sufficient time had lapsed following voiding of the calculus through the urethra for urinary tract infection to have resolved. To further define the prevalence and significance of urolithiasis, prosectors of dead stranded marine mammals are encouraged to closely observe their urinary and genital tracts for calculi and to submit them for quantitative analysis.     

New polymorphic tetranucleotide microsatellites improve scoring accuracy in the bottlenose dolphin Tursiops aduncus

We isolated and characterized 19 novel tetranucleotide microsatellite markers in the Indo-Pacific bottlenose dolphin (Tursiops aduncus) in order to improve genotyping accuracy in applications like large-scale population-wide paternity and relatedness assessments. One hundred T. aduncus from Shark Bay, Western Australia, were screened for polymorphism. Cross-amplification was tested on four other small odontocete species. The new tetranucleotide microsatellite loci showed a more than fourfold higher scoring accuracy and significantly lower stutter formation compared to eight dinucleotide loci, although overall allelic diversity was significantly reduced.     

The localization of the sound source in the vertical plane by a bottlenose dolphin

The accuracy of localizing the underwater sound source in the vertical-plane by the bottlenose dolphin was investigated using the method of instrumental conditioned reflexes with food reinforcement. The accuracy of determining the underwater sound in the vertical plane (the full angle) was on the average: 2 - 2,5 degrees for tonal signals with frequencies of 5, 20, and 120 kHz; pulsed clicks with the central frequency of 120 kHz and the exponential forms of amplitude alteration wavefronts were localized by the dolphin with an accuracy of 1,5 degrees. Among all marine mammals examined, dolphins are characterized by the maximal exact analysis of acoustic space.     

Orbital gland structure and secretions in the Atlantic bottlenose dolphin (Tursiops truncatus)

Orbital gland structure of the Atlantic bottlenose dolphin, Tursiops truncatus, was examined at the macroscopic, light microscopic, and electron microscopic levels. The gland completely encircles the ocular globe in a belt-like fashion near the conjunctival fornix but is considerably more developed medially. Duct openings are scattered throughout the fornix and over the surface of the palpebral conjunctiva. Microscopically, the gland has a tubuloalveolar arrangement; alveolar cells contain numerous secretory vesicles which can be interpreted as two structural types by light and electron microscopy. Histochemical staining demonstrates that both types contain glycosaminoglycans. Lipid analysis of the glandular secretion (dolphin tears) shows them to be non-oily and to contain only negligible amounts of cholesterol, triglycerides, phospholipids, and free fatty acids. The secretion is clear, slippery, and viscoelastic and well-adapted to protecting the eye and to reducing frictional forces between the eye surface and surrounding seawater.