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.     

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.     

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.     

Quantitative analysis of bottlenose dolphin movement patterns and their relationship with foraging

1. Broad-scale telemetry studies have greatly improved our understanding of the ranging patterns and habitat-use of many large vertebrates. However, there often remains considerable uncertainty over the function of different areas or the factors influencing habitat selection. Further insights into these processes can be obtained through analyses of finer scale movement patterns. For example, search behaviour may be modified in response to prey distribution and abundance. 2. In this study, quantitative analysis techniques are applied to the movements of bottlenose dolphins, recorded from land using a theodolite, to increase our understanding of their foraging strategies. Movements were modelled as a correlated random walk (CRW) and a biased random walk (BRW) to identify movement types and using a first-passage time (FPT) approach, which quantifies the time allocated to different areas and identifies the location and spatial scale of intensive search effort. 3. Only a quarter of the tracks were classed as CRW movement. Turning angle and directionality appeared to be key factors in determining the type of movement adopted. A high degree of overlap in search effort between separate movement paths indicated that there were small key sites (0.3 km radius) within the study area (4 km(2)). Foraging behaviour occurred mainly within these intensive search areas, indicating that they were feeding sites. 4. This approach provides a quantitative method of identifying important foraging areas and their spatial scale. Such techniques could be applied to movement paths for a variety of species derived from telemetry studies and increase our understanding of their foraging strategies.     

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.     

Left hemispheric advantage for numerical abilities in the bottlenose dolphin

In a two-choice discrimination paradigm, a bottlenose dolphin discriminated relational dimensions between visual numerosity stimuli under monocular viewing conditions. After prior binocular acquisition of the task, two monocular test series with different number stimuli were conducted. In accordance with recent studies on visual lateralization in the bottlenose dolphin, our results revealed an overall advantage of the right visual field. Due to the complete decussation of the optic nerve fibers, this suggests a specialization of the left hemisphere for analysing relational features between stimuli as required in tests for numerical abilities. These processes are typically right hemisphere-based in other mammals (including humans) and birds. The present data provide further evidence for a general right visual field advantage in bottlenose dolphins for visual information processing. It is thus assumed that dolphins possess a unique functional architecture of their cerebral asymmetries.     

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.     

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.     

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.     

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.     

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.     

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.     

Effect of lactation stage and concurrent pregnancy on milk composition in the bottlenose dolphin

Although many toothed whales (Cetacea: Odontoceti) lactate for 2–3 years or more, it is not known whether milk composition is affected by lactation stage in any odontocete species. We collected 64 pooled milk samples spanning 1–30 months postpartum from three captive bottlenose dolphins Tursiops truncatus . Milks were assayed for water, fat, crude protein (TN × 6.38) and sugar; gross energy was calculated. Ovulation and pregnancy were determined via monitoring of milk progesterone. Based on analysis of changes in milk composition for each individual dolphin, there were significant increases ( P <0.05) in fat (in all three dolphins) and crude protein (in two of three), and a decrease ( P <0.05) in water (in two of three) over the course of lactation, but the sugar content did not change. In all three animals, the energy content was positively correlated with month of lactation, but the percentage of energy provided by crude protein declined slightly but significantly ( P <0.05). At mid-lactation (7–12 months postpartum, n =17), milk averaged 73.0±1.0% water, 12.8±1.0% fat, 8.9±0.5% crude protein, 1.0±0.1% sugar, 1.76±0.09 kcal g⁻¹ (=7.25 kJ g⁻¹) and 30.3±1.3% protein:energy per cent. This protein:energy per cent was surprisingly high compared with other cetaceans and in relation to the growth rates of calves. Milk progesterone indicated that dolphins ovulated and conceived between 413 and 673 days postpartum, following an increase in milk energy density. The significance of these observed compositional changes to calf nutrition will depend on the amounts of milk produced at different stages of lactation, and how milk composition and yield are influenced by sampling procedure, maternal diet and maternal condition, none of which are known.     

Thirty year retrospective evaluation of pneumonia in a bottlenose dolphin Tursiops truncatus population

Pneumonia is one of the most common causes of morbidity in bottlenose dolphins Tursiops truncatus. To better understand associations of pneumonia with demographics, microbiology, pathology, and histopathology, a retrospective study on 42 dolphins from the US Navy Marine Mammal Program dolphin population was conducted (1980 to 2010). A total of 21 (50%) of the dolphins evaluated had pneumonia confirmed by histopathology. Bacterial and fungal pneumonia was present in 42.9 and 28.6% of cases (9 and 6 cases), respectively, with Staphylococcus aureus as the most common confirmed pathogen (4 cases, 19%). Other pathogens identified as the cause of pneumonia were Cryptococcus neoformans, Erysipelothrix rhusiopathiae, Histoplasma capsulatum, parainfluenza virus, Proteus species, Pseudomonas aeruginosa, and Streptococcus zooepidemicus. Neither sex nor age was a predictor of pneumonia. While many of the infections involved disseminated disease, lungs were consistently the most severely affected organs. The present study demonstrates the high susceptibility of dolphins to respiratory infections. Areas that warrant further investigation include eosinophilic pneumonia, chronic infections, co-infections, and metabolic or iron-storage diseases. There is a continuing need to improve the early diagnosis and effective treatment of pneumonia in dolphins.