The follicle-sinus complex of the bottlenose dolphin (Tursiops truncatus). Functional anatomy and possible evolutional significance of its somato-sensory innervation.

Vibrissae are tactile hairs found mainly on the rostrum of most mammals. The follicle, which is surrounded by a large venous sinus, is called "follicle-sinus complex" (FSC). This complex is highly innervated by somatosensitive fibers and reached by visceromotor fibers that innervate the surrounding vessels. The surrounding striated muscles receive somatomotor fibers from the facial nerve. The bottlenose dolphin (Tursiops truncatus), a frequently described member of the delphinid family, possesses this organ only in the postnatal period. However, information on the function of the vibrissal complex in this latter species is scarce. Recently, psychophysical experiments on the river-living Guiana dolphin (Sotalia guianensis) revealed that the FSC could work as an electroreceptor in murky waters. In the present study, we analyzed the morphology and innervation of the FSC of newborn (n = 8) and adult (n = 3) bottlenose dolphins. We used Masson's trichrome stain and antibodies against neurofilament 200 kDa (NF 200), protein gene product (PGP 9.5), substance P (SP), calcitonin gene-related peptide, and tyrosine hydroxylase (TH) to characterize the FSC of the two age classes. Masson's trichrome staining revealed a structure almost identical to that of terrestrial mammals except for the fact that the FSC was occupied only by a venous sinus and that the vibrissal shaft lied within the follicle. Immunostaining for PGP 9.5 and NF 200 showed somatosensory fibers finishing high along the follicle with Merkel nerve endings and free nerve endings. We also found SP-positive fibers mostly in the surrounding blood vessels and TH both in the vessels and in the mesenchymal sheath. The FSC of the bottlenose dolphin, therefore, possesses a rich somatomotor innervation and a set of peptidergic visceromotor fibers. This anatomical disposition suggests a mechanoreceptor function in the newborns, possibly finalized to search for the opening of the mother's nipples. In the adult, however, this structure could change into a proprioceptive function in which the vibrissal shaft could provide information on the degree of rotation of the head. In the absence of psychophysical experiments in this species, the hypothesis of electroreception cannot be rejected.

Ecological divergence and speciation in common bottlenose dolphins in the western South Atlantic.

Coastal and offshore ecotypes of common bottlenose dolphins have been recognized in the western South Atlantic, and it is possible that trophic niche divergence associated with social interactions is leading them to genetic and phenotypic differentiation. The significant morphological differentiation observed between these ecotypes suggests they represent two different subspecies. However, there is still a need to investigate whether there is congruence between morphological and genetic data to rule out the possibility of ecophenotypic variation accompanied by gene flow. Mitochondrial DNA (mtDNA) control region sequence data and 10 microsatellite loci collected from stranded and biopsied dolphins sampled in coastal and offshore waters of Brazil as well as 106 skulls for morphological analyses were used to determine whether the morphological differentiation was supported by genetic differentiation. There was congruence among the data sets, reinforcing the presence of two distinct ecotypes. The divergence may be relatively recent, however, given the moderate values of mtDNA nucleotide divergence (dA = 0.008), presence of one shared mtDNA haplotype and possibly low levels of gene flow (around 1% of migrants per generation). Results suggest the ecotypes may be in the process of speciation and reinforce they are best described as two different subspecies until the degree of nuclear genetic divergence is thoroughly evaluated: Tursiops truncatus gephyreus (coastal ecotype) and T. t. truncatus (offshore ecotype). The endemic distribution of T. t. gephyreus in the western South Atlantic and number of anthropogenic threats in the area reinforces the importance of protecting this ecotype and its habitat.

Evaluation of respiratory vapour and blubber samples for use in endocrine assessments of bottlenose dolphins (Tursiops spp.).

Blubber and respiratory vapour ('blow') are now commonly used for endocrine studies on cetaceans, primarily because they can be obtained using minimally invasive methods. For many species, these samples have yet to be validated for these purposes. The objective of this study was to examine the performance of blow and blubber hormone monitoring, relative to serum hormone monitoring, for evaluating the reproductive and adrenal condition of captive bottlenose dolphins (Tursiops spp.). Eighteen bottlenose dolphins were sampled five times for serum and blow and twice for blubber throughout a one-year period. Concentrations of progesterone, testosterone, oestradiol and cortisol were measured in each sample type. Hormone levels were examined in relation to dolphin age, sex, reproductive status, season, time of sample collection (morning/afternoon) and collection type (in- or out-of-water sampling). Patterns in hormone levels were similar for serum and blubber. For instance, in both sample types, progesterone levels were significantly higher in pregnant (serum: 34.10 ±â€¯8.64 ng/mL; blubber: 13.01 ±â€¯0.72 ng/g) than in non-pregnant females (serum: 0.32 ±â€¯0.09 ng/mL; blubber: 1.17 ±â€¯0.10 ng/g). This pattern was not detected in blow, primarily because seawater contamination, nylon sampling materials and variable sample volumes influenced measured concentrations. In addition, the respiratory water content of a blow sample is known to affect measured hormone levels. Two methods were trialled to control for variability in sample volumes and dilution: (1) normalising blow hormone concentrations relative to urea nitrogen levels (a potential endogenous standard), and (2) measuring the relative proportions (i.e. ratios) of blow hormones. These correction measures had little influence on blow hormone results. Further refinement of blow hormone monitoring methods is required before they can be used for reproductive or adrenal assessments of bottlenose dolphins. Blubber, on the other hand, should be a suitable proxy for serum when attempting to classify pregnancy status and male maturity in these species.

Non-auditory, electrophysiological potentials preceding dolphin biosonar click production.

The auditory brainstem response to a dolphin's own emitted biosonar click can be measured by averaging epochs of the instantaneous electroencephalogram (EEG) that are time-locked to the emitted click. In this study, averaged EEGs were measured using surface electrodes placed on the head in six different configurations while dolphins performed an echolocation task. Simultaneously, biosonar click emissions were measured using contact hydrophones on the melon and a hydrophone in the farfield. The averaged EEGs revealed an electrophysiological potential (the pre-auditory wave, PAW) that preceded the production of each biosonar click. The largest PAW amplitudes occurred with the non-inverting electrode just right of the midline-the apparent side of biosonar click generation-and posterior of the blowhole. Although the source of the PAW is unknown, the temporal and spatial properties rule out an auditory source. The PAW may be a neural or myogenic potential associated with click production; however, it is not known if muscles within the dolphin nasal system can be actuated at the high rates reported for dolphin click production, or if sufficiently coordinated and fast motor endplates of nasal muscles exist to produce a PAW detectable with surface electrodes.

Comprehensive endocrine response to acute stress in the bottlenose dolphin from serum, blubber, and feces.

Several hormones are potential indicators of stress in free-ranging animals and provide information on animal health in managed-care settings. In response to stress, glucocorticoids (GC, e.g. cortisol) first appear in circulation but are later incorporated into other tissues (e.g. adipose) or excreted in feces or urine. These alternative matrices can be sampled remotely, or by less invasive means, than required for blood collection and are especially valuable in highly mobile species, like marine mammals. We characterized the timing and magnitude of several hormones in response to a stressor in bottlenose dolphins (Tursiops truncatus) and the subsequent incorporation of cortisol into blubber, and its metabolites excreted in feces. We evaluated the endocrine response to an acute stressor in bottlenose dolphins under managed care. We used a standardized stress protocol where dolphins voluntarily beached onto a padded platform and remained out of water for two hours; during the stress test blood samples were collected every 15 min and blubber biopsies were collected every hour (0, 60, and 120 min). Each subject was studied over five days: voluntary blood samples were collected on each of two days prior to the stress test; 1 and 2 h after the conclusion of the out-of-water stress test; and on the following two days after the stress test. Fecal samples were collected daily, each afternoon. The acute stressor resulted in increases in circulating ACTH, cortisol, and aldosterone during the stress test, and each returned to baseline levels within 2 h of the dolphin's return to water. Both cortisol and aldosterone concentrations were correlated with ACTH, suggesting both corticosteroids are at least partly regulated by ACTH. Thyroid hormone concentrations were generally unaffected by the acute stressor. Blubber cortisol increased during the stress test, and fecal GC excretion was elevated on the day of the stress test. We found that GCs in bottlenose dolphins can recover within hours of acute stress, and that cortisol release can be detected in alternate matrices within a few hours-within 2 h in blubber, and 3.5-5 h in fecal samples.

ESTABLISHING MARGINAL LYMPH NODE ULTRASONOGRAPHIC CHARACTERISTICS IN HEALTHY BOTTLENOSE DOLPHINS ( TURSIOPS TRUNCATUS).

Pulmonary disease has been well documented in wild and managed dolphin populations. The marginal lymph nodes of the dolphin thorax provide lymphatic drainage to the lungs and can indicate pulmonary disease. This study standardized a technique for rapid, efficient, and thorough ultrasonographic evaluation of the marginal lymph nodes in bottlenose dolphins ( Tursiops truncatus). Thoracic ultrasonography was performed on 29 clinically healthy adult bottlenose dolphins. Reference intervals for lymph node dimensions and ultrasonographic characteristics of marginal lymph nodes were determined from four transducer orientations: longitudinal, transverse, oblique, and an orientation optimized to the ultrasonographer's eye. The relationship between lymph node dimensions and dolphin age, sex, length, weight, origin, and management setting (pool versus ocean enclosure) were also evaluated. The mean marginal lymph nodes measured 5.26 cm in length (SD = 1.10 cm, minimum = 3.04 cm, maximum = 7.61 cm, reference interval [10th to 90th percentiles per node dimension] 3.78-6.55 cm) and 3.72 cm in depth (SD = 0.59 cm, minimum = 2.64, maximum = 5.38 cm, reference interval 2.98-4.50 cm). Sex, dolphin length, weight, and management setting had no effect on lymph node dimensions. Dolphins >30 yr of age had longer node lengths than dolphins 5-10 yr old. Node dimensions did differ between dolphins from various origins. Most commonly, the lymph node was found to be hyperechoic relative to surrounding soft tissues (98%) and to have irregular caudal borders (84%), ill-defined deep borders (83%), flat superficial border (67%), triangular or rounded triangle shape (59%), irregular cranial border (55%), and moderate heterogeneity (34%). The data reported in this study serve as a baseline reference that may contribute to earlier detection of pleural and pulmonary disease of managed and wild cetacean populations.

The Neocortex of Indian River Dolphins (Genus Platanista): Comparative, Qualitative and Quantitative Analysis.

We investigated the morphology of four primary neocortical projection areas (somatomotor, somatosensory, auditory, visual) qualitatively and quantitatively in the Indian river dolphins (Platanista gangetica gangetica, P. gangetica minor) with histological and stereological methods. For comparison, we included brains of other toothed whale species. Design-based stereology was applied to the primary neocortical areas (M1, S1, A1, V1) of the Indian river dolphins and compared to those of the bottlenose dolphin with respect to layers III and V. These neocortical fields were identified using existing electrophysiological and morphological data from marine dolphins as to their topography and histological structure, including the characteristics of the neuron populations concerned. In contrast to other toothed whales, the visual area (V1) of the 'blind' river dolphins seems to be rather small. M1 is displaced laterally and the auditory area (A1) is larger than in marine species with respect to total brain size. The layering is similar in the cortices of all the toothed whale brains investigated; a layer IV could not be identified. Cell density in layer III is always higher than in layer V. The maximal neuron density in P. gangetica gangetica is found in layer III of A1, followed by layers III in V1, S1, and M1. The cell density in layer V is at a similar level in all primary areas. There are, however, some differences in neuron density between the two subspecies of Indian river dolphins. Taken as a whole, it appears that the neocortex of platanistids exhibits a considerable expansion of the auditory field. Even more than other toothed whales, they seem to depend on their biosonar abilities for navigation, hunting, and communication in their riverine habitat.

Ecological opportunities and specializations shaped genetic divergence in a highly mobile marine top predator.

Environmental conditions can shape genetic and morphological divergence. Release of new habitats during historical environmental changes was a major driver of evolutionary diversification. Here, forces shaping population structure and ecotype differentiation ('pelagic' and 'coastal') of bottlenose dolphins in the North-east Atlantic were investigated using complementary evolutionary and ecological approaches. Inference of population demographic history using approximate Bayesian computation indicated that coastal populations were likely founded by the Atlantic pelagic population after the Last Glacial Maxima probably as a result of newly available coastal ecological niches. Pelagic dolphins from the Atlantic and the Mediterranean Sea likely diverged during a period of high productivity in the Mediterranean Sea. Genetic differentiation between coastal and pelagic ecotypes may be maintained by niche specializations, as indicated by stable isotope and stomach content analyses, and social behaviour. The two ecotypes were only weakly morphologically segregated in contrast to other parts of the World Ocean. This may be linked to weak contrasts between coastal and pelagic habitats and/or a relatively recent divergence. We suggest that ecological opportunity to specialize is a major driver of genetic and morphological divergence. Combining genetic, ecological and morphological approaches is essential to understanding the population structure of mobile and cryptic species.

Comparative anatomy of the ophthalmic rete and its relationship to ocular blood flow in three species of marine mammal.

OBJECTIVE: To examine the blood supply to the eyes of bottlenose dolphin (Tursiops truncatus), spotted seal (Phoca largha), and California sea lion (Zalophus californianus). Emphasis is placed on exploring the anatomic function in the context of aquatic life. PROCEDURE: Methyl methacrylate casts were prepared and studied using a scanning electron microscope. Infrared images of the eye were recorded using a thermocamera. RESULTS: In all three marine species, blood is supplied to the ophthalmic rete. The main source of blood supply to the rete is the basilar rete via the spinal rete in the dolphin and via the ophthalmic artery in the seal and sea lion. The retinal and choroidal arteries are derived from the rete. The dolphin rete showed a very well-developed arterial network occupying most of the orbit. The rete in pinnipeds was less developed with several entwining arteries, unlike that in cetaceans. Thermographic examination revealed that the eye shows a higher degree of thermal emission than adjacent areas of the skin in these 3 species. DISCUSSION: The role of the rete in aquatic mammals appears to conserve ocular temperature so that the appropriate operating temperature for photoreceptors and ocular muscles can be maintained in a cold ambient temperature. Additionally, the rete might have a flow-damping effect by maintaining resistance to blood flow in the orbit. This study highlights the special nature of ocular vascular anatomy and function that enabled the unique adaptation of aquatic mammals to life in aquatic habitats.

[Mechanisms of sound reception and conduction in a dolphin].

Morphology of a lower jaw, model and behavioral experiments are discussed with the aim of exploring the mechanisms of sound reception and conduction to the dolphin's lower jaw canals taking into account known concepts of acoustics and a theory of group antennas. It is shown that the left and right row of mental foramens with the respective mandibular canal and tissues of the canals are forming the new outer ear and the new external auditory canal by which the sound (in frequency band of 0.1-160 kHz) is transmitted into the middle ear, in contrast to the dolphin's non-functional outer ear. This new external ear is created by nature as a receiving array of the traveling wave antenna located in the throat of the acoustical horn (a corresponding mandibular canal). The results give reason to assume the presence of similar new outer ear in Odontoceti.

The dive response redefined: underwater behavior influences cardiac variability in freely diving dolphins.

A hallmark of the dive response, bradycardia, promotes the conservation of onboard oxygen stores and enables marine mammals to submerge for prolonged periods. A paradox exists when marine mammals are foraging underwater because activity should promote an elevation in heart rate (f(H)) to support increased metabolic demands. To assess the effect of the interaction between the diving response and underwater activity on f(H), we integrated interbeat f(H) with behavioral observations of adult bottlenose dolphins diving and swimming along the coast of the Bahamas. As expected for the dive response, f(H) while resting during submergence (40±6 beats min(-1)) was significantly lower than f(H) while resting at the water surface (105±8 beats min(-1)). The maximum recorded f(H) (f(H,max)) was 128±7 beats min(-1), and occurred during post-dive surface intervals. During submergence, the level of bradycardia was modified by activity. Behaviors such as simple head bobbing at depth increased f(H) by 40% from submerged resting levels. Higher heart rates were observed for horizontal swimming at depth. Indeed, the dolphins operated at 37-58% of their f(H,max) while active at depth and approached 57-79% of their f(H,max) during anticipatory tachycardia as the animals glided to the surface. f(H) was significantly correlated with stroke frequency (range=0-2.5 strokes s(-1), r=0.88, N=25 dives) and calculated swim speed (range=0-5.4 m s(-1), r=0.88, N=25 dives). We find that rather than a static reflex, the dive response is modulated by behavior and exercise in a predictable manner.

Pulmonary ultrasound findings in a bottlenose dolphin Tursiops truncatus population.

Lung disease is common among wild and managed populations of bottlenose dolphins Tursiops truncatus. The purpose of the study was to apply standardized techniques to the ultrasound evaluation of dolphin lungs, and to identify normal and abnormal sonographic findings associated with pleuropulmonary diseases. During a 5 yr period (2005 to 2010), 498 non-cardiac thoracic ultrasound exams were performed on bottlenose dolphins at the Navy Marine Mammal Program in San Diego, California, USA. Exams were conducted as part of routine physical exams, diagnostic workups, and disease monitoring. In the majority of routine exams, no abnormal pleural or pulmonary findings were detected with ultrasound. Abnormal findings were typically detected during non-routine exams to identify and track disease progression or resolution; therefore, abnormal results are overrepresented in the study. In order of decreasing prevalence, abnormal sonographic findings included evidence of alveolar-interstitial syndrome, pleural effusion, pulmonary masses, and pulmonary consolidation. Of these findings, alveolar-interstitial syndrome was generally nonspecific as it represented several possible disease states. Pairing ultrasound findings with clinical signs was critical to determine relevance. Pleural effusion, pulmonary masses, and pulmonary consolidation were relatively straightforward to diagnose and interpret. Further diagnostics were performed to obtain definitive diagnoses when appropriate, specifically ultrasound-guided thoracocentesis, fine needle aspirates, and lung biopsies, as well as radiographs and computed tomography (CT) exams. Occasionally, post mortem gross necropsy and histopathology data were available to provide confirmation of diagnoses. Thoracic ultrasound was determined to be a valuable diagnostic tool for detecting pleural and pulmonary diseases in dolphins.

Dolphin biosonar signals measured at extreme off-axis angles: insights to sound propagation in the head.

Biosonar signals radiated along the beam axis of an Atlantic bottlenose dolphin resemble short transient oscillations. As the azimuth of the measuring hydrophones in the horizontal plane progressively increases with respect to the beam axis the signals become progressively distorted. At approximately ±45°, the signals begin to divide into two components with the time difference between the components increasing with increasing angles. At ±90° or normal to the longitudinal axis of the animal, the time difference between the two pulses measured by the hydrophone on the right side of the dolphin's head is, on average, ∼11.9 µs larger than the time differences observed by the hydrophone on the left side of the dolphin's head. The center frequency of the first pulse is generally lower, by 33-47 kHz, than the center frequency of the second pulse. When considering the relative locations of the two phonic lips, the data suggest that the signals are being produced by one of the phonic lips and the second pulse resulting from a reflection within the head of the animal. The generation of biosonar signals is a complex process and the propagation pathways through the dolphin's head are not well understood.

Evaluation of two-dimensional and three-dimensional ultrasound in the assessment of thyroid volume of the Indo-Pacific bottlenose dolphin (Tursiops aduncus).

The assessment of thyroid volume plays an indispensable role in the diagnosis and management of different thyroid diseases. The present study evaluates the accuracy of dolphin thyroid volume measurement as determined by four two-dimensional (2D) ultrasound methods (A-D), with a standard of reference using three-dimensional (3D) ultrasound. The measurement accuracy for different recognized thyroid configuration is also evaluated. Inter- and intraoperator variability of the measurement methods was determined. Thyroid ultrasound examinations were conducted in 16 apparently healthy Indo-Pacific bottlenose dolphins (Tursiops aduncus) with 2D and 3D ultrasound under identical scanning conditions. All 2D ultrasound measurement methods yielded high accuracies (79.9-81.3%) when compared with the 3D ultrasound measurement, and had high measurement reproducibility (77.6-86.2%) and repeatability (78.1-99.7%). For 2D ultrasound measurements, Methods A and B were more accurate and reliable than Methods C and D, regardless of thyroid configuration. Ultrasound is useful in the measurement of thyroid volume in bottlenose dolphins. For the first time, a reliable ultrasound scanning protocol for measuring dolphin thyroid volume was developed, which provides a means to establish a normative reference for the diagnosis of thyroid pathologies and to monitor the thyroid volume during the course of treatment in living dolphins. Key words: 3D ultrasound, Indo-Pacific bottlenose dolphin, thyroid volume measurement, Tursiops aduncus.

Behavioral and anatomical evidence for electroreception in the bottlenose dolphin (Tursiops truncatus).

In the order of cetacean, the ability to detect bioelectric fields has, up to now, only been demonstrated in the Guiana dolphin (Sotalia guianensis) and is suggested to facilitate benthic feeding. As this foraging strategy has also been reported for bottlenose dolphins (Tursiops truncatus), we studied electroreception in this species by combining an anatomical analysis of "vibrissal crypts" as potential electroreceptors from neonate and adult animals with a behavioral experiment. In the latter, four bottlenose dolphins were trained on a go/no-go paradigm with acoustic stimuli and afterward tested for stimulus generalization within and across modalities using acoustic, optical, mechanical, and electric stimuli. While neonates still possess almost complete vibrissal follicles including a hair shaft, hair papilla, and cavernous sinus, adult bottlenose dolphins lack these features. Thus, their "vibrissal crypts" show a similar postnatal morphological transformation from a mechanoreceptor to an electroreceptor as in Sotalia. However, innervation density was high and almost equal in both, neonate as well as adult animals. In the stimulus generalization tests the dolphins transferred the go/no-go response within and across modalities. Although all dolphins responded spontaneously to the first presentation of a weak electric field, only three of them showed perfect transfer in this modality by responding continuously to electric field amplitudes of 1.5 mV cm-1 , successively reduced to 0.5 mV cm-1 . Electroreception can explain short-range prey detection in crater-feeding bottlenose dolphins. The fact that this is the second odontocete species with experimental evidence for electroreception suggests that it might be widespread in this marine mammal group.

Histomorphological stratification of blubber of three dolphin species from subtropical waters.

Blubber is a highly specialized and dynamic tissue unique to marine mammals and presents a reflection of the individuals' nutrition, environment, and life history traits. Few studies have investigated the histomorphology of cetacean blubber in subtropical environments. The aim of this study was to investigate the blubber histomorphology of three different dolphin species off the subtropical KwaZulu-Natal coast, South Africa, using adipocyte cell size, number, and density. Blubber tissue samples from the saddle area of 43 incidentally bycaught animals (four Sousa plumbea, 36 Tursiops aduncus, and three Delphinus delphis) were used to compare cell parameters between blubber layers. Samples were divided into the upper third (corresponding to the superficial layer closest to the epidermis), middle third, and lower third (corresponding to the deep layer). For T. aduncus, factors potentially affecting blubber histomorphology, such as sex, age class, and season, were also assessed. Our results showed that no stratification was present in S. plumbea, which could be ascribed to the species' warmer inshore habitat, large body size, and apparent lower mobility. For T. aduncus and D. capensis, however, blubber stratification was determined, characterized by a gradual transition of cell size, number, and density between layers rather than clearly defined layers. Significant differences in adipocyte cell number and density were found for different sexes and age classes of T. aduncus. However, there were no significant differences between seasons, which was attributed to the small temperature differences between seasons. This study represents the first investigation of odontocete blubber histomorphology in subtropical waters. It is recommended that future studies investigate blubber lipid content, while also taking into consideration the reproductive status of the females and the temperature range of their study area. It is hoped that our results, in conjunction with histopathology and other health indicators, could assist in assessing health and body condition.

Pregnancy is a drag: hydrodynamics, kinematics and performance in pre- and post-parturition bottlenose dolphins (Tursiops truncatus).

Constraints on locomotion could be an important component of the cost of reproduction as carrying an increased load associated with eggs or developing fetuses may contribute to decreased locomotor performance for females across taxa and environments. Diminished performance could increase susceptibility to predation, yet the mechanism(s) by which gravidity and pregnancy affect locomotion remains largely unexplored. Here we demonstrate that morphology, hydrodynamics and kinematics were altered during pregnancy, providing a mechanism for diminished locomotor performance in two near-term pregnant (10 days pre-parturition) bottlenose dolphins (Tursiops truncatus). Near-term pregnancy resulted in a 56 ± 13% [corrected] increase in frontal surface area, coinciding with dramatic increases in drag forces while gliding. For example, pregnant females encountered 80 N of drag at 1.7 m s(-1) whereas that magnitude of drag was not encountered until speed doubled for females 18 months post-parturition. Indeed, drag coefficients based on frontal surface area were significantly greater during pregnancy (C(d,F)=0.22 ± 0.04) than at 18 months post-parturition (C(d,F)=0.09 ± 0.01). Pregnancy also induced a gait change as stroke amplitude and distance per stroke were reduced by 13 and 14%, respectively, compared with non-pregnant periods (1-24 months post-parturition). This was concomitant with a 62 and 44% reduction in mean and maximum swim speeds, respectively, during the pregnancy period. Interestingly, attack speeds of known predators of dolphins surpass maximum speeds for the pregnant dolphins in this study. Thus, pregnant dolphins may be more susceptible to predation. This study demonstrates unequivocally that changes in morphology, hydrodynamics and kinematics are associated with diminished performance during pregnancy in dolphins.

Stereology of the neocortex in Odontocetes: qualitative, quantitative, and functional implications.

We investigated the quantitative morphology of the neocortex (gray matter) in 2 toothed whale (odontocete) species (harbor porpoise, Phocoena phocoena; bottlenose dolphin, Tursiops truncatus) with stereological methods. The 4 primary projection areas (motor, somatosensory, auditory, and visual fields) are analyzed for their cell densities in layers III and V with standard design-based stereology methods. Along cortical areas M1, S1, A1, and V1 in Tursiops, neuron density is always higher in layer III than in layer V, whereas the data in Phocoena are variable. Moreover, neuron density in layer III is generally around 1.5 times higher in Tursiops than in Phocoena. Maximal density values are seen in layer III of A1 and V1 in Tursiops and the ratio of layer III/layer V density is maximal in A1 of this species. Thus, layer III could have a higher capacity in the bottlenose dolphin with regard to intrinsic connectivity. Extant knowledge on toothed whale neurobiology and behavior suggests that quantitative/stereological differences between the 2 odontocete species regarding the neuron density of standard cortical units may be correlated with specific adaptations to their respective habitats. In contrast to layers V and VI which mainly serve as an executive system, layer III could represent an intermediate level in sensory and premotor processing which works more tangentially in the cortices via horizontal connections with other cortical areas, respectively. The generally higher density of cortical layer III in Tursiops suggests a higher connectivity of this layer in view of the more agile and complicated behavior of these gregarious animals including versatile phonation by complex sound and ultrasound signals.

Neural time and movement time in choice of whistle or pulse burst responses to different auditory stimuli by dolphins.

Echolocating dolphins emit trains of clicks and receive echoes from ocean targets. They often emit each successive ranging click about 20 ms after arrival of the target echo. In echolocation, decisions must be made about the target--fish or fowl, predator or food. In the first test of dolphin auditory decision speed, three bottlenose dolphins (Tursiops truncatus) chose whistle or pulse burst responses to different auditory stimuli randomly presented without warning in rapid succession under computer control. The animals were trained to hold pressure catheters in the nasal cavity so that pressure increases required for sound production could be used to split response time (RT) into neural time and movement time. Mean RT in the youngest and fastest dolphin ranged from 175 to 213 ms when responding to tones and from 213 to 275 ms responding to pulse trains. The fastest neural times and movement times were around 60 ms. The results suggest that echolocating dolphins tune to a rhythm so that succeeding pulses in a train are produced about 20 ms over target round-trip travel time. The dolphin nervous system has evolved for rapid processing of acoustic stimuli to accommodate for the more rapid sound speed in water compared to air.

The acoustic field on the forehead of echolocating Atlantic bottlenose dolphins (Tursiops truncatus).

Arrays of up to six broadband suction cup hydrophones were placed on the forehead of two bottlenose dolphins to determine the location where the beam axis emerges and to examine how signals in the acoustic near-field relate to signals in the far-field. Four different array geometries were used; a linear one with hydrophones arranged along the midline of the forehead, and two around the front of the melon at 1.4 and 4.2 cm above the rostrum insertion, and one across the melon in certain locations not measured by other configurations. The beam axis was found to be close to the midline of the melon, approximately 5.4 cm above the rostrum insert for both animals. The signal path coincided with the low-density, low-velocity core of the melon; however, the data suggest that the signals are focused mainly by the air sacs. Slight asymmetry in the signals were found with higher amplitudes on the right side of the forehead. Although the signal waveform measured on the melon appeared distorted, when they are mathematically summed in the far-field, taking into account the relative time of arrival of the signals, the resultant waveform matched that measured by the hydrophone located at 1 m.