title: Exercise at depth alters bradycardia and incidence of cardiac anomalies in deep-diving marine mammals.
abstract: Unlike their terrestrial ancestors, marine mammals routinely confront extreme physiological and physical challenges while breath-holding and pursuing prey at depth. To determine how cetaceans and pinnipeds accomplish deep-sea chases, we deployed animal-borne instruments that recorded high-resolution electrocardiograms, behaviour and flipper accelerations of bottlenose dolphins (Tursiops truncatus) and Weddell seals (Leptonychotes weddellii) diving from the surface to >200 m. Here we report that both exercise and depth alter the bradycardia associated with the dive response, with the greatest impacts at depths inducing lung collapse. Unexpectedly, cardiac arrhythmias occurred in >73% of deep, aerobic dives, which we attribute to the interplay between sympathetic and parasympathetic drivers for exercise and diving, respectively. Such marked cardiac variability alters the common view of a stereotypic 'dive reflex' in diving mammals. It also suggests the persistence of ancestral terrestrial traits in cardiac function that may help explain the unique sensitivity of some deep-diving marine mammals to anthropogenic disturbances.
authors.affiliation: Department of Ecology and Evolutionary Biology, Center for Ocean Health, University of California Santa Cruz, Santa Cruz, California 95060, USA.
authors.forename: Terrie M
authors.initials: TM
authors.lastname: Williams
authors.affiliation: Marine Science Institute, The University of Texas at Austin, Port Aransas, Texas 78373-5015, USA.
authors.forename: Lee A
authors.initials: LA
authors.lastname: Fuiman
authors.affiliation: Department of Ecology and Evolutionary Biology, Center for Ocean Health, University of California Santa Cruz, Santa Cruz, California 95060, USA.
authors.forename: Traci
authors.initials: T
authors.lastname: Kendall
authors.affiliation: Epcot's The Seas-Walt Disney World Resorts, Lake Buena Vista, Florida 32830-1000, USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: Berry
authors.affiliation: Department of Ecology and Evolutionary Biology, Center for Ocean Health, University of California Santa Cruz, Santa Cruz, California 95060, USA.
authors.forename: Beau
authors.initials: B
authors.lastname: Richter
authors.affiliation: Department of Ecology and Evolutionary Biology, Center for Ocean Health, University of California Santa Cruz, Santa Cruz, California 95060, USA.
authors.forename: Shawn R
authors.initials: SR
authors.lastname: Noren
authors.affiliation: Department of Ecology and Evolutionary Biology, Center for Ocean Health, University of California Santa Cruz, Santa Cruz, California 95060, USA.
authors.forename: Nicole
authors.initials: N
authors.lastname: Thometz
authors.affiliation: Cardiovascular Division, The Rayne Institute, St Thomas' Hospital, London SE1 7EH, UK.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Shattock
authors.affiliation: Marine Science Institute, The University of Texas at Austin, Port Aransas, Texas 78373-5015, USA.
authors.forename: Edward
authors.initials: E
authors.lastname: Farrell
authors.affiliation: Epcot's The Seas-Walt Disney World Resorts, Lake Buena Vista, Florida 32830-1000, USA.
authors.forename: Andy M
authors.initials: AM
authors.lastname: Stamper
authors.affiliation: Department of Marine Biology, Texas A&M University, 200 Seawolf Parkway, Ocean and Coastal Sciences Building, Galveston, Texas 77554, USA.
authors.forename: Randall W
authors.initials: RW
authors.lastname: Davis
mesh_terms: D000818:Animals; D001919:Bradycardia / Q000378:metabolism / Q000503:physiopathology*; D004242:Diving / Q000502:physiology*; D004289:Dolphins / Q000502:physiology; D004734:Energy Metabolism / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D046048:Seals, Earless / Q000502:physiology; D013550:Swimming / Q000502:physiology