(Presented by April Pini and KT Matheny)

Our paper discussed the following:

• The transfer of heat from terrestrial mammals. During exercise as heat production and blood flow increase, terrestrial mammals can transfer excess heat to the environment by 4 pathways:
• Conduction
• Convection
• Radiation
• Evaporation
• Prior study done with terrestrial mammals studying heat production and muscle blood flow (Mitchell 1977).
• Marine mammals have blubber to insulate themselves so they utilize poorly insulated areas to transfer heat, they also use:
• Conduction
• Convection
• Counter-current heat exchange makes it possible for marine mammals to cool their blood down, by passing the blood through these poorly insulated areas, known as thermal windows.
• Some problems between the dive response and the counter-current heat exchange.
• The amount of blood flow to peripheral areas is reduced during diving to conserve oxygen, this also limits the amount of blood available for heat dissipation.
• This shows that there is a direct conflict between the cardiovascular requirements and the diving response.
• This study was done to observe thermoregulation in bottlenose dolphins and the changes in heat flow and skin temperature. We did a comparison of the levels of heat flow of animals at the surface and the heat flow levels of animals submerged in water.
• Previous studies have been done measuring deep body temperature of bottlenose and Hawaiian spinner dolphins during rest, surface swimming and leaps and spins in the pool (Hampton et al. 1971).
• Three adult Atlantic bottlenose dolphins were studied, two males and one female.
• They were kept in salt-water pens that connected to the ocean near the Grand Bahama Island.
• We observed the animals heat flow levels while they were
• At rest on the surface
• Post-exercise on the surface
• Post-exercise at a depth of 15 meters
• The skin temperature was taken at three different sites: the dorsal fin, flank, and underside of the fluke blade.
• The results showed that there was not much variation in the skin temperature.
• The lowest skin temp. were found for resting and post-exercise submerged dolphins.
• Measuring the heat flow on the surface showed that:
• The dolphins gave off more heat at the surface after exercising.
• The heat from the peripheral sites remained elevated at least 10 min. into the recovery period, and didn’t begin to decrease until about 20 min. into recovery.
• Measuring the heat flow at depth showed that:
• Reductions of 30-67% were observed from the two peripheral sites at depth.
• Heat flow from both the dorsal fin and the fluke were lower during post-exercise dive than during post-exercise on surface.
• The mammalian dive response to exercise involves a redistribution of blood to the skin, in marine mammals this response is complicated by the circulatory adjustments associated with diving.
• Important components of the mammalian dive response are bradycardia and decreased peripheral blood flow as found by Scholander 1940.
• We found that heat transfer from the thermal windows was attenuated by the dive response.
• Our expected results were that
• Dolphins would have a shorter recovery period than terrestrial mammals.
• Our actual results were that
• The recovery period for dolphins is very similar to that of terrestrial mammals.
• Some factors that may have contributed:
• The temp. differential between water and body core was less than 8° C
• The peripheral windows only represent 30% of total surface area of the dolphins
• The balance between diving and thermoregulation responses
• There may be an override of the dive response during heat stress
• Previous study on restrained harbor seals (Hammel et al. 1977) and ducks (Johansen 1964) showed an override of the dive response during heat stress.
• The balance depends on the level of activity and the depth of submergence

References

Cossins, AR. and K. Bowler. Temperature Biology of Animals. London, Chapman and Hall, 1987

Hammel HT, Elsner RW, Heller HC, Maggert JA, Bainton CR (1977) Thermoregulatory responses to altering hypothalamic temperature in the harbor seal. Am J Physiol 232: R18-R26

Hampton IFG, Whittow GC, Szekerczes J, Rutherford S (1971) Heat transfer and body temperature in the Atlantic bottlenose dolphin, Tursiops truncatus. Int J Biometeorol 15:247-253

Handrich Y, Bevan RM, Charrassin JB, et al. (1997) Hypothermia in foraging king penguins. Nature 388: 64-67

Johansen K (1964) Regional distribution of the circulating blood during submersion asphyxia in the duck. Acta Physiol Scand 62: 1-9

Mitchell JW (1977) Energy exchanges during exercise. In: Nadel ER (ed) Problems with temperature regulation during exercise. Academic Press, New York, pp 11-26

Prosser, CL and F. Brown (1961) Comparative Animal Physiology

Scholander PF (1940) Experimental investigations on the respiratory function in diving mammals and birds. Hvalradets Skr Norske Videnskaps-Akad 22: 1-131

Williams TM, Friedl WA, Fong ML, et al. (1992) Travel at low energetic cost by swimming and wave-riding bottlenose dolphins. Nature 355: 821-823

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