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Circadian organization of an animal lacking a pineal organ; the young American alligator,Alligator mississippiensis


Circadian rhythms were examined in young American alligators,Alligator mississippiensis, an animal that naturally lacks a pineal organ. Individual alligators displayed persistent, stable, free-running circadian activity rhythms under both constant darkness and constant illumination. Free-running activity was entrained by 24 h light-dark cycles. The circadian period length was also temperature compensated, with Q10's of 1.0–1.40 obtained for a 22–32 °C interval. The presence of this quite ‘normal’ circadian rhythmicity in alligators indicates that the pineal organ is not always essential for the expression of circadian rhythms in lower vertebrates.

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This research was supported by grant NS 12257 for N.I.H. to C.L. Ralph. Alligators were obtained through the courtesy of C.R. Tracy and T. Joanen of the Rockefeller Wildlife Refuge, Grand Chenier, Louisiana.

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Kavaliers, M., Ralph, C.L. Circadian organization of an animal lacking a pineal organ; the young American alligator,Alligator mississippiensis . J. Comp. Physiol. 139, 287–292 (1980).

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  • Circadian Rhythm
  • Activity Rhythm
  • Period Length
  • Lower Vertebrate
  • Constant Darkness