PHYSIOLOGICAL-MECHANISMS FOR UNDERWATER ENDURANCE - CANADA GOOSE (BRANTA-CANADENSIS) VERSUS PEKIN DUCK (ANAS-PLATYRHYNCHOS)

Maximum submergence time of Canada geese was 18% of that of similarly sized Pekin ducks, Due to a smaller respiratory system volume the oxyg en store of Canada geese was 82% of that of Pekin ducks, accounting fo r approximately 33% of the difference in underwater survival times, Th e respiratory properties and volume of the blood were similar in both species. Both species utilised approximately 79% of the respiratory ox ygen store and 90% of the blood oxygen store. Therefore, most of the s pecies difference in survival times was due to a less effective oxygen -conserving cardiovascular response (bradycardia, peripheral vasoconst riction) in Canada geese, Duck cardiac chronotropic sensitivity to hyp oxia during submergence was twice that observed in geese. Furthermore, a lower hypoxic ventilatory response was observed in geese than in du cks. Density of monoamine varicosities in hindlimb artery walls was lo wer in geese than ducks. However, electrical stimulation of the hindli mb muscles did not cause ascending vasodilatation during submergence i n either species, perhaps due to higher levels of catecholamines in su bmerged geese. We conclude that the major difference between species i s higher oxygen chemosensitivity in ducks which effects a much more ra pid and efficacious oxygen-conserving response during forced submergen ce.