This study analyses the aortic wall structure in nine cetacean species with deep diving habits belonging to four Odontoceti families: Ziphiidae, Kogiidae, Physteridae, and Delphinidae. Samples of ascending, thoracic and abdominal aorta were processed for histological and morphometric studies. The elastic component was higher in the proximal aortic segments, and the muscular elements increased distally in all cases. Morphometric analyses showed that all families presented a decrease in the thickness of the arterial wall and the tunica media along the aorta. The reduction was dramatic between ascending and thoracic aorta in the Physeteridae specimens; meanwhile, the other three families showed a more uniform decrease between the ascending, thoracic and abdominal aorta. The decline was not correlated with a reduced elastic or lamellar unit thickness but with a loss of lamellar units. The organization of the elements in the aortic wall did not show essential modifications between the four families, resembling the structure described previously in the shallow and intermediate diving dolphins. Our findings support that the difference in the morphometric characteristics of the different segments in the aortic wall is likely related to the diving habit more than the absolutes values of any other parameter.

The pituitary gland regulates essential physiological processes in mammals. Despite its importance, research on its anatomy and ultrastructure in dolphins remains scarce. Using non-invasive imaging technology (MRI) and a novel skull-opening and dissection protocol, this study characterizes the dolphin pituitary through immunohistochemistry (IHC) and transmission electron microscopy (TEM). A total of 47 pituitaries were collected from stranded common bottlenose dolphins (Tursiops truncatus). common dolphins (Delphinus delphis), and Atlantic spotted dolphins (Stenella frontalis). as well as from captive common bottlenose dolphins. MRI allowed visualization of the gland’s anatomy and its spatial relationship with the hypothalamus and surrounding structures. A modified skull-opening and pituitary extraction protocol ensured the preservation of the adenohypophysis and neurohypophysis for detailed analysis. Histological, immunohistochemical, and ultrastructural studies confirmed the gland’s structural organization, identifying eight distinct adenohypophyseal cell types: corticotrophs (ACTH), somatotrophs (GH), gonadotrophs (FSH and LH), lactotrophs (LTH), melanotrophs (MSH), thyrotrophs (TSH), follicular cells, and capsular cells. This study presents the first immunolabelling of thyrotrophs in cetacean adenohypophysis and the first detailed ultrastructural characterization of adenohypophyseal cells in cetaceans, providing baseline data for future research. By integrating multidisciplinary techniques, it advances the understanding of dolphin neuroendocrinology and highlights broader implications for cetacean health, welfare, and conservation.

Cetaceans are mammals that underwent a series of evolutionary adaptations to live in the aquatic environment, including morphological modifications of various anatomical structures of the skeleton and their bone mineral density (BMD); there are few studies on the latter. BMD is related to the radiodensity measured through computed tomography (CT) in Hounsfield units (HU). This work aimed to test and validate the usefulness of studying humeral bone radiodensity by CT of two cetacean species (the Atlantic spotted dolphin and the pygmy sperm whale) with different swimming and diving habits. The radiodensity was analysed at certain levels following a new protocol based on a review of previous studies. Humeral radiodensity values were related to four aspects: species, diving behaviour, swimming activity level, and age. We observed that the consistent differences in the radiodensity of the cortical bone of the distal epiphysis between animals of different life-history categories suggest that this bone portion could be particularly useful for future ontogenetic studies. Hence, this technique may be helpful in studying and comparing species with different ecophysiologies, particularly distinguishing between swimming and diving habits.

Climate change, overfishing, and other anthropogenic activities can negatively impact the energetic balance and body condition of cetaceans. Still, cetaceans must meet their energetic demands for survival, which are more expensive to maintain in the marine environment. The resilience of cetaceans to negative energy balance periods is unknown. We analyzed where striped dolphins, a medium‐sized dolphin with shallow‐intermediate diving habits, and Blainville's beaked whales, a larger odontocete with an extreme diving profile, store their energy reserves and how they use that energy. We performed dissections of body mass compartments of fresh dead adults of similar total body lengths but different body masses, determined the lipid and protein content of blubber and muscle, and calculated oxygen stores and the aerobic dive limit. Proteins in muscle were the largest source of energy stores for both species, followed by lipids in the blubber and muscle. Both species catabolized blubber and muscle simultaneously when losing body mass to avoid impairing other important functions. When these functions are impaired, a cascade of increased field metabolic rate and decreased energy intake may occur, decreasing their resilience to environmental challenges and making them more susceptible to diseases, ultimately resulting in death by starvation.