title: Resting breathing frequency in aquatic mammals: a comparative analysis with terrestrial species.
abstract: Several species of aquatic mammals, while resting at the water surface, breathe with a low frequency (f). We asked if this was a general characteristic of mammals adapted to life in water. Measurements of f were obtained in 42 aquatic mammals of 19 species, during resting conditions. Data of additional 10 species were available from the literature. The allometric function for aquatic mammals was f=33W(-0.42) (f, breaths/min; W, kg; N=29, one data point per species, from six mammalian orders). This exponent was significantly different from that of the allometric curve of terrestrial mammals (W(-0.25)). The difference between aquatic and terrestrial species was small up to about 10kg, and widened with the increase in W. Out of several possibilities, it seems that the breath-holding response to favour buoyancy at the water surface could have contributed to the evolution of the low-f breathing, but a satisfactory explanation for the allometric pattern of f is still unavailable. In semi-aquatic mammals the low-f pattern observed at the water surface was maintained ashore, with no difference in the allometric function. As in the adult, also in the newborn of aquatic species f was low, compared to same-size neonates of terrestrial species. Hence, the low f has evolved to be part of the genetic makeup of aquatic mammals, retained when the animal is ashore, and already expressed at birth.
authors.affiliation: Department of Physiology, McGill University, Basic Science Building, Room 1121, 3655 Sir William Osler Promenade, Montreal, Que., Canada H3G 1Y6. jacopo.mortola@mcgill.ca
authors.forename: Jacopo P
authors.initials: JP
authors.lastname: Mortola
authors.forename: Marie-Josée
authors.initials: MJ
authors.lastname: Limoges
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D000831:Animals, Newborn; D002940:Circadian Rhythm; D005260:Female; D008168:Lung / Q000502:physiology; D008297:Male; D008322:Mammals / Q000502:physiology*; D012018:Reflex; D015656:Respiratory Mechanics; D012146:Rest; D014867:Water
chemical_list: D014867:Water