![]() 4) and mainly related to the distribution of its definitive hosts (see Section 5). Thus, its geographical range appears to be wide ( Fig. sima from Philippine waters ( Quiazon et al., 2013). ziphidarum was also found in a specimen of K. ![]() cavirostris from Chilean waters ( Mattiucci and Nascetti, 2008, unpublished data). After its first morphological description and genetic characterization ( Paggi et al., 1998) (see Section 4), this species has been recently identified genetically as an adult in other species of beaked whales, such as Mesoplodon mirus, Mesoplodon densirostris, and Mesoplodon grayi from the South Atlantic waters (off South Africa coast), from Mesoplodon europaeus of Caribbean sea ( Cavallero et al., 2011 Colón-Llavina et al., 2009), from Mesoplodon bowdoini of New Zealand waters ( Mattiucci et al., 2009), as well as from other geographical areas, such as its occurrence in Mesoplodon sp. cavirostris from the South Atlantic Ocean (off the South African coast). It was first described, both genetically and morphologically, as an adult in the beaked whales Mesoplodon layardii and Z. 9, 10 Studies of competitive free divers have demonstrated increased total lung capacity, splenic volume, hypercarbia tolerance, and hemoglobin concentration. 8 The Bajau, who spend up to 60% of their working day breath-holding at depths of more than 70 m, have genetic adaptations that increase spleen size and modify their human diving reflex. The Japanese Ama pearl divers and Bajau (“sea nomads”) of Southeast Asia are two of the human populations most closely studied for their diving adaptations. Triggered by apnea and cold-water facial immersion, this dive response includes bradycardia (which decreases oxygen consumption), peripheral vasoconstriction (which shunts blood to vital organs), and splenic contraction (which increases circulating red blood cell volume). 7Īll diving mammals, including humans, have developed a characteristic physiologic response to diving. Collectively, these adaptations and adaptive behaviors aim to increase oxygen delivery to the vital organs, minimize potentially fatal consequences of absorbing compressed oxygen or nitrogen at extreme depths, and avoid painful compression or rupture of air-filled structures. Certain diving mammals (e.g., seals) even exhale before diving. In fact, some of the deepest-diving whales have markedly small lung volumes relative to body mass. ![]() 5, 6 Contrary to popular belief, increasing total lung capacity is not a uniform adaptation in diving mammals. 4 Many diving mammals have evolved to possess many specialized adaptations, including larger spleens, high mass-specific blood volumes (>200 mL/kg in sperm whales as compared with 70 mL/kg in human adults), enhanced myoglobin structure and distribution, anatomic adaptations of the middle ear and sinuses, and specialized intrathoracic anatomy. 3 Some diving mammals (Cuvier’s beaked whales ) reach depths of nearly 3000 m on dives lasting more than 2 hours. Diving Weddell seals ( Leptonychotes weddellii) have reached arterial partial pressures of oxygen (P o 2) of 18 mm Hg during 27-minute dives and may reach much lower partial pressures during dives known to last nearly 45 minutes. Several aquatic species are among the most hypoxia-tolerant animals on the planet. Many air-breathing animals have developed remarkable adaptations for diving and survival underwater. Courtney Broaddus MD, in Murray & Nadel's Textbook of Respiratory Medicine, 2022 Adaptation to Diving
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