Physiological Adjustments to Prolonged Diving in the American Alligator Alligator mississippiensis

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Abstract
Conspicuous physiological adjustments to experimental submersion have been observed in the natural divers among the birds and the mammals. In order to obtain further information on the phenomena associated with water immersion, and to explore these characteristics in other diving vertebrates, experiments have been carried out on the American alligator, Alligator mississippiensis. The heart rate was found to slow down during diving. The pressure induced in the large arteries by ventricular systole diminished only gradually during diastole, probably due to an increased peripheral resistance resulting from a marked vasoconstriction in certain vascular beds. This thesis was supported by the fact that lactic acid formed in the muscles during diving did not appear in the blood until after emersion, suggesting that the blood flow through the muscles is greatly reduced while the animals dive. The alligator may recover easily from a submergence lasting until the oxygen stores are almost completely depleted. These results indicate that the “diving reflexes” occur in a wide variety of vertebrate divers belonging to different phylogenetic groups. They also support the following conclusions: The circulatory adjustments, by shutting off the perfusion to certain vascular beds, enable the alligator to make the limited oxygen stores last throughout prolonged periods of submersion. The animal remains in a state of useful consciousness until the oxygen stores are almost exhausted. This serves to extend the safety 4 margin for prolonged diving and ensure a complete utilization of the oxygen available.

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