Tursiops Truncatus Research Articles

Blubber biopsy in common bottlenose dolphins using a novel biopsy puncher: Evaluation of the impact on living individuals and possibility of applications in cetacean research.

Biopsy has recently become a preferred protocol for sampling the skin and blubber of many cetacean species, although it is desirable to collect as minimally invasive as possible. Here, the effect of biopsy sampling on the captive common bottlenose dolphins was evaluated by analyzing the process of wound healing and changes in hematological and blood biochemical parameters after biopsy using a puncher developed to collect up to the inner layer of the dolphin blubber. Results showed that the wounds caused by biopsy were closed in as early as 1 day and completely covered with the epidermis within 5-11 days. Blood fibrinogen, which generally increases due to a wound-induced inflammatory response or activation of the coagulation system, was significantly elevated after the biopsy indicating ongoing tissue repair, while other parameters did not exhibit significant differences. Furthermore, histological observation and RNA extraction of samples were performed to investigate the versatility of this method to cetacean research. Histological examination revealed three distinct layers of the blubber in the biopsy samples. Moreover, total RNA extracted from biopsy samples exhibited sufficient quality and quantity for gene expression analyses. Overall, the puncher utilized in our study represents a valuable and minimally invasive tool for investigating various aspects of small cetacean studies.

Conservation energetics of beluga whales: using resting and swimming metabolism to understand threats to an endangered population.

The balance between energetic costs and acquisition in free-ranging species is essential for survival, and provides important insights regarding the physiological impact of anthropogenic disturbances on wild animals. For marine mammals such as beluga whales (Delphinapterus leucas), the first step in modeling this bioenergetic balance requires an examination of resting and active metabolic demands. Here, we used open-flow respirometry to measure oxygen consumption during surface rest and submerged swimming by trained beluga whales, and compared these measurements with those of a commonly studied odontocete, the Atlantic bottlenose dolphin (Tursiops truncatus). Both resting metabolic rate (3012±126.0 kJ h-1) and total cost of transport (1.4±0.1 J kg-1m-1) of beluga whales were consistent with predicted values for moderately sized marine mammals in temperate to cold-water environments, including dolphins measured in the present study. By coupling the rate of oxygen consumption during submerged swimming with locomotor metrics from animal-borne accelerometer tags, we developed predictive relationships for assessing energetic costs from swim speed, stroke rate and partial dynamic acceleration. Combining these energetic data with calculated aerobic dive limits for beluga whales (8.8 min), we found that high-speed responses to disturbance markedly reduce the whale's capacity for prolonged submergence, pushing the cetaceans to costly anaerobic performances that require prolonged recovery periods. Together, these species-specific energetic measurements for beluga whales provide two important metrics, gait-related locomotor costs and aerobic capacity limits, for identifying relative levels of physiological vulnerability to anthropogenic disturbances that have become increasingly pervasive in their Arctic habitats.

Polychlorinated biphenyls in mussels, small pelagic fish, tuna, turtles, and dolphins from the Croatian Adriatic Sea waters: an overview of the last two decades of monitoring.

This review summarises our two decades of polychlorinated biphenyl (PCB) monitoring in different marine organisms along the eastern Adriatic Sea. The aim was to gain an insight into the trends of PCB distribution in order to evaluate the effectiveness of past and current legislation and suggest further action. Here we mainly focus on PCB levels in wild and farmed Mediterranean mussels, wild and farmed bluefin tuna, loggerhead sea turtles, common bottlenose dolphins, and small pelagic fish. The use of artificial intelligence and advanced statistics enabled an insight into the influence of various variables on the uptake of PCBs in the investigated organisms as well as into their mutual dependence. Our findings suggest that PCBs in small pelagic fish and mussels reflect global pollution and that high levels in dolphins and wild tuna tissues raise particular concern, as they confirm their biomagnification up the food chain. Therefore, the ongoing PCB monitoring should focus on predatory species in particular to help us better understand PCB contamination in marine ecosystems in our efforts to protect the environment and human health.

Moderate Anthropogenic Noise Exposure Does Not Affect Navy Bottlenose Dolphin (Tursiops truncatus) Whistle Rates

Bottlenose dolphins (Tursiops truncatus) rely on frequency- and amplitude-modulated whistles to communicate, and noise exposure can inhibit the success of acoustic communication through masking or causing behavioral changes in the animal. At the US Navy Marine Mammal Program (MMP) in San Diego, CA, dolphins are housed in netted enclosures in the San Diego Bay and exposed to noise from vessels, unmanned underwater vehicles, and other remote sensing devices. The acoustic behavior of 20 dolphins was monitored and whistle rates during noise events were quantified. Whistle rates during the onset of the event (i.e., the first 5 min) did not significantly differ from the pre-onset (5 min immediately preceding). Whistle rates were also not significantly different for the entire duration of the event compared to a matched control period. The noise’s frequency range (i.e., control, mid-frequency (0–20 kHz) or high-frequency (21–80 kHz)), signal-to-noise ratio, and sound pressure level were not significantly related to the dolphins’ whistle rate. Considering this is a location of frequent and moderate noise output, these results lend support to established guidelines on anthropogenic noise exposure for cetaceans, suggesting that moderate noise exposure levels may not impact communication efforts in bottlenose dolphins.

Thrust production and chordal flexion of the flukes of bottlenose dolphins performing tail stands at different efforts.

Dolphins have become famous for their ability to perform a wide variety of athletic and acrobatic behaviors including high-speed swimming, maneuverability, porpoising and tail stands. Tail stands are a behavior where part of the body is held vertically above the water's surface, achieved through thrust produced by horizontal tail fluke oscillations. Strong, efficient propulsors are needed to generate the force required to support the dolphin's body weight, exhibiting chordwise and spanwise flexibility throughout the stroke cycle. To determine how thrust production, fluke flexibility and tail stroke kinematics vary with effort, six adult bottlenose dolphins (Tursiops truncatus) were tested at three different levels based on the position of the center of mass (COM) relative to the water's surface: low (COM below surface), medium (COM at surface) and high (COM above surface) effort. Additionally, fluke flexibility was measured as a flex index (FI=chord length/camber length) at four points in the stroke cycle: center stroke up (CU), extreme top of stroke (ET), center stroke down (CD) and extreme bottom of stroke (EB). Video recordings were analyzed to determine the weight supported above the water (thrust production), peak-to-peak amplitude, stroke frequency and FI. Force production increased with low, medium and high efforts, respectively. Stroke frequency also increased with increased effort. Amplitude remained constant with a mean 33.8% of body length. Significant differences were seen in the FI during the stroke cycle. Changes in FI and stroke frequency allowed for increased force production with effort, and the peak-to-peak amplitude was higher compared with that for horizontal swimming.

General health status of a stranded Tursiops truncatus of the oceanic ecotype in southern Gulf of Mexico, Campeche coasts: a multidisciplinary analysis

Strandings provide valuable information about rare marine organisms and their relationship with their environment. In the southern Gulf of México, specifically on the central coast of Campeche, Mexico, strandings of oceanic cetaceans have rarely been recorded, therefore, biological information has also been scarce. One of such rare stranding cases occurred on September 7, 2022, on the coast of Seybaplaya, Campeche. The specimen was identified as a female of Tursiops truncatus with the morphology features of the oceanic ecotype. The carcass was examined shortly after death, and samples for different analyses were obtained fresh. Tissue samples were collected, and some particular observations were made to define the individual's general health status. Results of the analyses revealed damage in the liver, lungs, and kidneys, probably related to 1) the advanced age of the organism (>35 years), and 2) the presence of persistent organic pollutants. Most importantly, this study contributed two new findings, the first record of the parasite Anisakis and the presence of renal calculi in the oceanic ecotype of T. truncatus in the southern Gulf of Mexico.

Environmental drivers of odontocete occurrence in a nearshore temperate habitat

Nearshore coastal waters off Northumberland, UK, are important habitats for marine megafauna including marine mammals and seabirds. The area also features extensive anthropogenic activities including shipping, marine renewables development, fisheries, and tourism. Meanwhile there is lack of baseline data on odontocete occurrence to allow assessment of the potential impact from human disturbance. A recent increase in the number of sightings of common bottlenose dolphins (Tursiops truncatus) in the area has provided impetus for new data to inform conservation managers and policy makers. To provide this information, acoustic data were collected using broadband passive acoustic recorders at three sites (Druridge Bay, Newbiggin-by-the-Sea, and St Mary's Island) off the Northumberland coast and analyzed to identify species-specific click trains of common bottlenose dolphin, white-beaked dolphin (Lagenorhynchus albirostris) and harbor porpoise (Phocoena phocoena). Detection data were modelled for each species as detection-positive hours (DPH) using Generalized Additive Models with Generalized Estimating Equations (GAM-GEE) to investigate the effects of environmental covariates, including day of year, diel phase, lunar phase, salinity, year, month and sea surface temperature, and their interaction with location. A total of 20,845 h were recorded during the study resulting in a total of 1660, 71, and 1111 DPH identified for bottlenose dolphin, white-beaked dolphin and porpoise, respectively. The final model for bottlenose dolphins retained all covariates except tidal index and an interaction between location and day of year after model selection and all covariates in the final model were significant. The final model for white-beaked dolphin retained month, year, location, diel index, temperature, lunar index and interactions between location and diel index and all covariates except lunar index were significant. The final model for porpoise retained all covariates and interactions between location and diel phase, day of year, lunar index, and salinity, however, salinity and the interaction between location and lunar index were not significant. Bottlenose dolphin clicks were detected in the area year-round but with two peak periods in occurrence coinciding with May and late September; white-beaked dolphin clicks were detected predominantly in July and August; and porpoise clicks were present year-round but with much greater probability of detection at the Druridge Bay site, where there were peaks in winter and in September. The results of this study provide important information for conservation and management actions that may be needed to reduce anthropogenic pressures on odontocetes in UK waters.

Dolphin-WET-Development of a Welfare Evaluation Tool for Bottlenose Dolphins (Tursiops truncatus) under Human Care.

Ensuring high standards of animal welfare is not only an ethical duty for zoos and aquariums, but it is also essential to achieve their conservation, education, and research goals. While for some species, animal welfare assessment frameworks are already in place, little has been done for marine animals under human care. Responding to this demand, the welfare committee of the European Association for Aquatic Mammals (EAAM) set up a group of experts on welfare science, cetacean biology, and zoo animal medicine across Europe. Their objective was to develop a comprehensive tool to evaluate the welfare of bottlenose dolphins (Tursiops truncatus), named Dolphin-WET. The tool encompasses 49 indicators that were either validated through peer review or management-based expertise. The first of its kind, the Dolphin-WET is a species-specific welfare assessment tool that provides a holistic approach to evaluating dolphin welfare. Inspired by Mellor's Five Domains Model and the Welfare Quality®, its hierarchical structure allows for detailed assessments from overall welfare down to specific indicators. Through combining 37 animal-based and 12 resource-based indicators that are evaluated based on a two- or three-level scoring, the protocol offers a detailed evaluation of individual dolphins. This approach allows for regular internal monitoring and targeted welfare management, enabling caretakers to address specific welfare concerns effectively.

Passive acoustic monitoring and visual sighting survey of cetacean occurrence patterns in the Kingdom of Saudi Arabia

AbstractThe available data on occurrence patterns of cetaceans in the Red Sea area of the Kingdom of Saudi Arabia is very limited. The dearth of information is of pressing conservation concern as the coastline is undergoing rapid development as part of the Kingdom's effort to diversify its national economy. To understand how these developments will impact cetaceans in the region, the first large‐scale acoustic and visual survey in the Kingdom's part of the Gulf of Aqaba and the northeastern Red Sea was undertaken in 2020. The results of the acoustic surveys reveal 3.6 encounters per 100 km of track line of odontocete species with variable distribution across the study area. No baleen whale vocalizations were detected. Through visual surveys, five odontocete species were identified within the study area: Tursiops truncatus, T. aduncus, Stenella attenuata, S. longirostris, and two opportunistic sightings of a single Grampus griseus.

Distribution of calcium-binding proteins immunoreactivity in the bottlenose dolphin entorhinal cortex.

The entorhinal cortex has been shown to be involved in high-level cognitive functions in terrestrial mammals. It can be divided into two main areas: the lateral entorhinal area (LEA) and the medial entorhinal area (MEA). Understanding of its structural organization in cetaceans is particularly important given the extensive evidence for their cognitive abilities. The present study describes the cytoarchitectural and immunohistochemical properties of the entorhinal cortex of the bottlenose dolphin (Tursiops truncatus, Montagu, 1821), perhaps the most studied cetacean species and a paradigm for dolphins and other small cetaceans. Four bottlenose dolphins' entorhinal cortices were processed. To obtain a precise overview of the organization of the entorhinal cortex we used thionin staining to study its laminar and regional organization, and immunoperoxidase technique to investigate the immunohistochemical distribution of three most commonly used calcium-binding proteins (CBPs), calbindin D-28k (CB), calretinin (CR) and parvalbumin (PV). Entorhinal cortex layers thickness were measured, morphological and morphometric analysis for each layer were conducted and statistically compared. Six layers in both the LEA and MEA were identified. The main difference between the LEA and the MEA is observed in layers II and III: the neurons in layer II of the LEA were denser and larger than the neurons in layer II of MEA. In addition, a relatively cell-free zone between layers II and III in LEA, but not in MEA, was observed. The immunohistochemical distribution of the three CBPs, CB, CR and PV were distinct in each layer. The immunostaining pattern of CR, on one side, and CB/PV, on the other side, appeared to be distributed in a complementary manner. PV and CB immunostaining was particularly evident in layers II and III, whereas CR immunoreactive neurons were distributed throughout all layers, especially in layers V and VI. Immunoreactivity was expressed by neurons belonging to different morphological classes: All CBPs were expressed in non-pyramidal neurons, but CB and CR were also found in pyramidal neurons. The morphological characteristics of pyramidal and non-pyramidal neurons in the dolphin entorhinal cortex are similar to those described in the entorhinal cortex of other species, including primates and rodents. Interestingly, in primates, rodents, and dolphins, most of the CBP-containing neurons are found in the superficial layers, but the large CR-ir neurons are also abundant in the deep layers. Layers II and III of the entorhinal cortex contain neurons that give rise to the perforant pathway, which conveys most of the cortical information to the hippocampal formation. From the hippocampal formation, reciprocal projections are directed back to the deep layer of the entorhinal cortex, which distributes the information to the neocortex and subcortical area. Our data reveal that in the dolphin entorhinal cortex, the three major CBPs label morphologically heterogeneous groups of neurons that may be involved in the information flow between entorhinal input and output pathways.

Evaluation of the safety and efficacy of fecal microbiota transplantations in bottlenose dolphins (Tursiops truncatus) using metagenomic sequencing.

Gastrointestinal disease is a leading cause of morbidity in bottlenose dolphins (Tursiops truncatus) under managed care. Fecal microbiota transplantation (FMT) holds promise as a therapeutic tool to restore gut microbiota without antibiotic use. This prospective clinical study aimed to develop a screening protocol for FMT donors to ensure safety, determine an effective FMT administration protocol for managed dolphins, and evaluate the efficacy of FMTs in four recipient dolphins. Comprehensive health monitoring was performed on donor and recipient dolphins. Fecal samples were collected before, during, and after FMT therapy. Screening of donor and recipient fecal samples was accomplished by in-house and reference lab diagnostic tests. Shotgun metagenomics was used for sequencing. Following FMT treatment, all four recipient communities experienced engraftment of novel microbial species from donor communities. Engraftment coincided with resolution of clinical signs and a sustained increase in alpha diversity. The donor screening protocol proved to be safe in this study and no adverse effects were observed in four recipient dolphins. Treatment coincided with improvement in clinical signs.

Urinalysis Reference Intervals between Rough-Toothed Dolphins (Steno bredanensis) and Common Bottlenose Dolphins (Tursiops truncatus) Kept Under Human Care

Urinalysis Reference Intervals between Rough-Toothed Dolphins (Steno bredanensis) and Common Bottlenose Dolphins (Tursiops truncatus) Kept Under Human Care

Evidence of a small, island-associated population of common bottlenose dolphins in the Mariana Islands

Small, island-associated populations of cetaceans have evolved around numerous oceanic islands, likely due to habitat discontinuities between nearshore and offshore waters. However, little is known about the ecology and structure of cetacean populations around the Mariana Islands, a remote archipelago in the western Pacific Ocean. We present sighting, photo-identification, and genetic data collected during twelve years of surveys around these islands that reveal the existence of a small, island-associated population of bottlenose dolphins. Nearly half of the photo-identified individuals were encountered in more than one year. Both haplotypic and nuclear genetic diversity among sampled individuals was low (haplotypic diversity = 0.701, nuclear heterozygosity = 0.658), suggesting low abundance. We used mark-recapture analysis of photo-identification data to estimate yearly abundance in the southern portion of the population’s range from 2011 to 2018. Each abundance estimate was less than 54 individuals, with each upper 95% confidence interval below 100. Additional survey effort is necessary to generate a full population abundance estimate. We found extensive introgression of Fraser’s dolphin DNA into both the mitochondrial and nuclear genomes of the population, suggesting at least two hybridization events more than two generations in the past. The Mariana Islands are used extensively by the U.S. military for land and sea training operations. Thus, this unique bottlenose dolphin population likely faces high exposure to multiple threats.

Contact Exchanges in Bottlenose Dolphin Mother–Calf Pairs

The relationship between a dolphin mother and her calf has been well studied, but details regarding tactile exchanges within these dyads are limited. Contacts between five adult female bottlenose dolphins (Tursiops truncatus) and their calves, with data from three pairs analyzed statistically, were examined from video collected in October 2017, 2018, 2019, and in January 2018. Of 289 contact events, calves initiated 65.7% (n = 190), of which 82.6% (n = 157) were affiliative; 77.8% (n = 77) of mother-initiated contacts were categorized similarly. Thus, the overall trend for mother–calf contacts was affiliative. Mothers initiated contact with the dorsal fin less often (n = 3), while calves initiated with their dorsal fin more often (n = 40), especially one-year-old (C1) calves (n = 33). The body was used to initiate contact more by three-year-old (C3) calves (n = 47) and less by C1 calves (n = 22). Both results are likely an artifact of the infant position used by calves at different developmental stages. Only two-year-old (C2) calves initiated agonistic contact with their rostrum (n = 4); 75% of these contacts were initiated by one male calf. Mothers used the body to initiate contact with most calf ages, though contact by pectoral fin occurred more often than expected with their C2 calves (n = 11). Since 72.7% of these contacts came from one mother, a specific maternal style may be present. Only one mother used her rostrum with her C3 calf to initiate agonistic contacts; all others used the fluke. Several variables, including individual preference, calf sex, and maternal experience, may explain some of the contact patterns, but a larger sample size is needed to illustrate potential patterns among pairs. Still, these results support the notion that mother–calf dyads share more affiliative than agonistic contacts, expanding our knowledge on the tactile relationships of mother–calf pairs.

First Record of a Piebald Bottlenose Dolphin (Tursiops truncatus) in Australian Waters

First Record of a Piebald Bottlenose Dolphin (Tursiops truncatus) in Australian Waters

Estimations of length-weight relationships and consumption rates of odontocetes in the Mediterranean Sea from stranding data

Stranding data provide fundamental information on biometric traits of cetaceans useful to increase knowledge on ecological traits and their consumption patterns. In this study, the length weight (L-W) relationships through the power regression model (W=a×Lb) were calculated for three dolphin species (the striped dolphin, the common bottlenose dolphin and the Risso's dolphin) in several Mediterranean subregions and at the scale of the entire basin. Length (L) and weight (W) data were collected from stranding records during the period from 1983 to 2021 acquired from several databases and the literature. Starting from L-W relationships, a bootstrap method was applied to estimate the mean body weights, the daily ingested biomass (IB) and annual food consumption (AFC) rates of different dolphin species. In particular, four different equations were used to estimate the IB rates. Prey consumption by dolphin species was calculated through AFC rates and the available diet information (expressed in weight fractions) of dolphin species for different Mediterranean subregions.Considering the L-W relationships in the Mediterranean Sea, b coefficient values were equal to 2.578, 2.975 and 2.988 for the striped, the common bottlenose and the Risso's dolphin, respectively. At the Mediterranean scale, the AFC values estimated were 3913 kg (CI 2469–5306) for the Risso's dolphin, 2571 kg (1372–3963) for the common bottlenose dolphin and 1118 kg (531–1570) for the striped dolphin. Prey consumption pattern showed a clear partitioning among the investigated species, where the common bottlenose dolphin exploits neritic demersal and pelagic fishes (e.g. eel fishes, sparids), the striped dolphin exploits mesopelagic fishes and myctophids, and the Risso's dolphin was specialized on bathyal cephalopods of Histioteuthidae family.The results obtained in this study provide new information for the investigated species in several Mediterranean subregions providing a first consistent baseline to support the population dynamics modelling. At the same time, the wide uncertainty ranges of some parameters, as well as the lack of information for some species, stress the necessity of improving the data collection associated to stranding events, especially in the southern Mediterranean areas.

Agonistic interactions initiated by adult bottlenose dolphins on Antillean manatee calves in the Caribbean Sea.

The dynamics and drivers of inter-species interactions in the wild are poorly understood, particularly those involving social animal species. Inter-species interactions between cetaceans and sirenians have rarely been documented and investigated. Here, we report 10 cases of interaction initiated by adult bottlenose dolphins (Tursiops truncatus) towards Antillean manatee (Trichechus manatus manatus). Interactions were documented through behavioral observations in the wild (n = 7) and from the examination of orphaned calves (i.e., tooth rake marks on their body; n = 4) that entered a rehabilitation facility, one individual both observed interacting with dolphins and found stranded with bite marks. Bottlenose dolphins were observed interacting with orphan manatee calves and with mother-calf pairs, exhibiting agonistic behavior (n = 2), affiliative or neutral behaviors (n = 1), but the behavioral contexts of these interactions remain unclear in most cases (n = 7). Information on stranded individuals was collected from four calves (of 13 examined calves) recovered in poor condition with bottlenose dolphin tooth rakes and bite wounds on their bodies, one of which died. Injury from bite wounds varied in extent and severity, ranging from superficial scratches leaving rake marks to deep lacerations. Our findings suggest the regular occurrence of agonistic behaviors initiated by adult bottlenose dolphins and directed toward manatee calves. However, the drivers of these interactions remain unknown and need to be further investigated.

Application of novel burst wave lithotripsy and ultrasonic propulsion technology for the treatment of ureteral calculi in a bottlenose dolphin (Tursiops truncatus) and renal calculi in a harbor seal (Phoca vitulina)

Marine mammals may develop kidney stones, which can be challenging to treat. We describe burst wave lithotripsy (BWL) and ultrasonic propulsion to treat ureteral calculi in a 48-year-old female bottlenose dolphin (Tursiops truncatus) and to reduce renal stone burden in a 23-year-old male harbor seal (Phoca vitulina). BWL and ultrasonic propulsion were delivered transcutaneously in sinusoidal ultrasound bursts to fragment and reposition stones. Targeting and monitoring were performed with real-time imaging integrated within the BWL system. Four dolphin stones were obtained and fragmented ex vivo. The dolphin case received a 10-min and a 20-min BWL treatment conducted approximately 24 h apart to treat two 8–10 mm partially obstructing right mid-ureteral stones, using oral sedation alone. For the harbor seal, while under general anesthesia, retrograde ureteroscopy attempts were unsuccessful because of ureteral tortuosity, and a 30-min BWL treatment was targeted on one 10-mm right kidney stone cluster. All 4 stones fragmented completely to < 2-mm fragments in < 20 min ex vivo. In the dolphin case, the ureteral stones appeared to fragment, spread apart, and move with ultrasonic propulsion. On post-treatment day 1, the ureteral calculi fragments shifted caudally reaching the ureteral orifice on day 9. On day 10, the calculi fragments passed, and the hydroureter resolved. In the harbor seal, the stone cluster was observed to fragment and was not visible on the post-operative computed tomography scan. The seal had gross hematuria and a day of behavior indicating stone passage but overall, an uneventful recovery. BWL and ultrasonic propulsion successfully relieved ureteral stone obstruction in a geriatric dolphin and reduced renal stone burden in a geriatric harbor seal.

Age-related changes in the primary auditory cortex of newborn, adults and aging bottlenose dolphins (Tursiops truncatus) are located in the upper cortical layers.

The auditory system of dolphins and whales allows them to dive in dark waters, hunt for prey well below the limit of solar light absorption, and to communicate with their conspecific. These complex behaviors require specific and sufficient functional circuitry in the neocortex, and vicarious learning capacities. Dolphins are also precocious animals that can hold their breath and swim within minutes after birth. However, diving and hunting behaviors are likely not innate and need to be learned. Our hypothesis is that the organization of the auditory cortex of dolphins grows and mature not only in the early phases of life, but also in adults and aging individuals. These changes may be subtle and involve sub-populations of cells specificall linked to some circuits. In the primary auditory cortex of 11 bottlenose dolphins belonging to three age groups (calves, adults, and old animals), neuronal cell shapes were analyzed separately and by cortical layer using custom computer vision and multivariate statistical analysis, to determine potential minute morphological differences across these age groups. The results show definite changes in interneurons, characterized by round and ellipsoid shapes predominantly located in upper cortical layers. Notably, neonates interneurons exhibited a pattern of being closer together and smaller, developing into a more dispersed and diverse set of shapes in adulthood. This trend persisted in older animals, suggesting a continuous development of connections throughout the life of these marine animals. Our findings further support the proposition that thalamic input reach upper layers in cetaceans, at least within a cortical area critical for their survival. Moreover, our results indicate the likelihood of changes in cell populations occurring in adult animals, prompting the need for characterization.

Vascularization of the gastrointestinal tract of the bottlenose dolphin (Tursiops truncatus, Montagu 1821).

Odontocetes primarily rely on fish, cephalopods, and crustaceans as their main source of nutrition. In the digestive system, their polygastric complex exhibits similarities to that of their closest terrestrial relatives such as cows, sheep, and giraffes, while the entero-colic tract shares similarities with terrestrial carnivores. The morphology, caliber, and structure of the odontocete intestine are relatively constant, and, since there is no caecum, a distinction between the small and large intestine and their respective subdivisions is difficult. To address this issue, we used the intestinal vascularization pattern, specifically the course and branching of the celiac artery (CA) and the cranial and caudal mesenteric arteries (CrMA and CdMA). A series of pictures and dissections of 10 bottlenose dolphins (Tursiops truncatus) were analyzed. Additionally, we performed a cast by injecting colored polyurethane foam in both arteries and veins to measure the caliber of the arteries and clarify their monopodial or dichotomous branching. Our results showed the presence of multiple duodenal arteries (DAs) detaching from the CA. The CrMA gave origin to multiple jejunal arteries, an ileocolic artery (ICA), and, in six cases, a CdMA. In four specimens, the CdMA directly originated from the abdominal aorta. The ICA gave rise to the mesenteric ileal branches (MIB) and mesenteric anti-ileal branches and the right colic arteries (RCA) and the middle colic arteries. From the CdMA originated the left colic and cranial rectal arteries (LCA and CrRA). The measurements revealed a mixed monopodial and dichotomous branching scheme. The analysis of the arteries and their branching gave us an instrument, based on comparative anatomy, to distinguish between the different intestinal compartments. We used the midpoint of anastomoses between MIB and RCA to indicate the border between the small and the large intestine, and the midpoint of anastomoses between LCA and CrRA, to tell the colon from the rectum. This pattern suggested an elongation of the duodenum and a shortening of the colic tract that is still present in this species. These findings might be related to the crucial need to possess a long duodenal tract to digest prey ingested whole without chewing. A short aboral part is also functional to avoid gas-producing colic fermentation. The rare origin of the CdMA on the CrMA might instead be a consequence of the cranial thrust of the abdominopelvic organs related to the loss of the pelvic girdle that occurred during the evolution of cetaceans.