Adaptations for Diving in Mammals By Peter Zervas

Complications of Diving Inability to extract oxygen from underwater environment This is a fancy way of saying that an animal with lungs cannot “breathe” water

Complications of Diving Low supply of O2 to organs intolerant of low levels of O2 Organs requiring high concentration of O2 Brain Heart Adrenal glands

Complications of Diving Pressurization of gasses due to increasing hydrostatic pressure Hydrostatic pressure increases with increasing depth At only 10 m, hydrostatic pressure is twice that of atmospheric pressure at sea level!

Complications of Diving Mobility in the water medium Terrestrial appendages are not designed for locomotion in water

Complications of Diving Loss of heat Most ocean water is cold (relative to air temp) Since mammals are homeothermic, excesive heat loss is a problem

General Adaptations Five general adaptations for diving 1.) Bradycardia 2.) Arterial Constriction/Blood Shunting 3.) High Concentration of Myoglobin in muscles 4.) Insulation 5.) Hydrodynamics

Bradycardia Part of “Mammalian Diving Reflex” Heart rate slows This leads to reduced consumption of O2 and plays a large role in prolonged diving

Arterial Constriction/Blood Shunting Again, triggered by diving reflex Arteries constrict near heart to limit blood flow to extremities Send less blood to: Viscera Muscles Leaves more blood for Heart Brain Adrenal gland Leads to more efficient use of O2 (Bron et al. 1966)

Higher Concentration of Myoglobin in the Muscles Myoglobin – primary oxygen-carrying pigment of mammalian muscles In Weddell seal (Leptonychotes weddellii) 25% of total oxygen during diving is stored in myoglobin Only 12% in humans

Insulation Blubber Fur Whales Pinnipeds (fin-footed mammals) Up to 2 inches thick over entire body Pinnipeds (fin-footed mammals) Up to 1/3 of entire weight Fur Phocid seals (true seals) 18,000 hairs/cm2 Otariid seals (sea lions) 57,000 hairs/cm2!!!!!!!!!!!!!!

Hydrodynamics Energetic costs to mammalian swimming estimated 2-23 times more expensive than in fish Leads to: Streamlining Swimming “gait” Period of continuous stroking Followed by prolonged period of gliding to max depth (Williams et al. 2000)

Leptonychotes weddellii

Leptonychotes weddellii Weddell Seal Storage of O2 5% of O2 in lungs and 75% in bloodstream Humans hold 36% in lungs and 51% in circulating blood Blood volume Almost twice the amount of blood per kilo of body weight compared to humans

Leptonychotes weddellii Spleen Can store up to 24 liters of O2 Spleen contracts during diving Releases O2 – rich blood into blood stream!!

Orcinus orca

Orcinus orca Collapsible lungs During diving, lungs collapse Force air out of lungs and into trachea and nasal cavities Trachea and nasal cavities do not abosrb N as well as the lungs

Orcinus orca Why is this advantageous? A condition known by divers as “the bends” occurs when divers come to the surface after a dive The rapid decompression of N (which is nearly 70% of air) causes bubbles in capillaries If there is no air the lungs to absorb during diving, there will be no N to cause these bubbles when returning to the surface

Works Cited Bron, K. M. et al. (1966). Arterial constrictor response in a diving mammal. Science, 152(3721),540-543. Williams et al. (2000). Sink or swim: Strategies for cost-efficient diving by marine mammals, Science, 288(5463),133-136.