Circannual Rhythms: Endogenous Annual Clocks in the Organization of Seasonal Processes(18 Zoophysiology)

In addition to the more or less static properties of the environ- ment, plants and animals must cope with its temporal variations. Among the most conspicuous temporal changes to which organisms are exposed are periodic phenomena generated by the rotation of the earth about its axis, its revolution around the sun, and the more complex movements of the moon in relation to both sun and earth. The first two of these astronomical cycles are basic to the familiar daily and annual rhythms, respectively, in the environment. The third generates somewhat more complex cycles, such as those in moonlight and variations in tides. These environmental cycles have provided challenges and opportunities for organisms to adjust their physiology and behavior to them. Indeed, the predictability inherent to these periodic processes has enabled organisms to evolve innate endogenous rhythmic programs that match the environmental cycles and allow, in a variety of different ways, adjustment of biological activities to the cycles of environmental changes. The endogenous nature of rhythmicity was first clearly recognized in the 1930's in daily periodicities, the most widely distributed and best investigated class of biological rhythms of this type. In the 1950's, demonstrations of endogenous tidal and lunar rhythms, which occur in some littoral and marine organisms, ensued. Another decade passed before endogenous annual periodicities were first demonstrated unambiguously.

Table of Contents:
1. Introduction.- 1.1 The Phenomenon of Annual Rhythmicity.- 1.2 Ultimate and Proximate Factors in the Control of Annual Rhythms.- 1.2.1 Ultimate Factors.- 1.2.2 Proximate Factors.- 1.3 Circannual Rhythms.- 1.4 Hierarchical Organization of Proximate Factors.- 1.5 Early Suggestions of Circannual Rhythms.- 1.5.1 Mammalian Hibernation and Avian Migration.- 1.5.2 Yearly Breeding Cycles in Tropical and Temperate-Zone Animals.- 1.5.3 Ten-Month Breeding Cycles in Tropical Birds.- 1.5.4 Plants.- 1.5.5 Development of the Oscillator Analogy.- 1.6 Some Definitions and Delimitations.- 2. Evidence for Circannual Rhythms.- 2.1 Typical Cases.- 2.1.1 Mammals.- 2.1.2 Birds.- 2.1.3 Lower Vertebrates.- 2.1.4 Invertebrates.- 2.1.5 Plants.- 2.2 Atypical Cases.- 3. Properties of Free-Running Circannual Rhythms.- 3.1 Degree of Persistence and Range of Permissive Conditions.- 3.2 Range of Circannual Period Length and Transients.- 3.3 Dependence of Period on External Conditions.- 3.3.1 Temperature.- 3.3.2 Photoperiod.- 3.3.3 Social Factors.- 3.4 Innateness of Circannual Rhythms.- 3.5 Comparison with Circadian Rhythms.- 4. Synchronization of Circannual Rhythms.- 4.1 Zeitgebers.- 4.1.1 Photoperiod.- 4.1.2 Ambient Temperature.- 4.1.3 Social Stimuli.- 4.2 Ranges of Entrainment.- 4.3 Behavoir Within the Range of Entrainment.- 4.4 Comparison with Circadian Rhythms and Some Conclusions.- 5. Mechanisms of Circannual Organization.- 5.1 Interactions with the Circadian System.- 5.1.1 Frequency Demultiplication of Circadian Rhythms.- 5.1.1.1 Relationship Between Circadian and Circannual Period Length.- 5.1.1.2 Effects of Disrupting the Circadian System on Circannual Rhythmicity.- 5.1.1.3 General Properties of Circannual Rhythms in Conflict with the Model.- 5.1.2 Circannual Rhythm of a Circadian Rhythm in Photosensitivity.- 5.1.3 Circannual Variations in the Internal Circadian System.- 5.1.3.1 Relationship Between States of Circadian and Circannual System.- 5.1.3.2 Internal Coincidence Between Circadian Neurotransmitter Rhythms as the Basis of Circannual Changes?.- 5.2 Interrelationship Among Different Circannual Functions. Or: One or Several Circannual Clocks?.- 5.2.1 Differential Degrees of Persistence of Various Circannual Functions.- 5.2.2 Internal Dissociation of Various Circannual Functions.- 5.2.3 Selective Manipulation of Rhythmic Functions.- 5.2.4 Conclusions.- 5.3 Components of Specific Circannual Functions.- 5.3.1 Attempts at Changing Circannual Period by Altering the Duration of Potential Components of the Cycle.- 5.3.2 Attempts at Identifying External and Internal Conditions Under Which Rhythmicity Stops or Continues.- 5.3.3 Identification of Hormones and Central Nervous Structures Involved in the Control of Circannual Rhythms.- 5.4 Conclusions.- 6. Adaptive Significance of Circannual Rhythms.- 6.1 General Advantages of Circannual Rhythms.- 6.1.1 Improvement of Consistency of Seasonal Timing.- 6.1.1.1 Hibernating Mammals.- 6.1.1.2 Migratory Birds.- 6.1.2 Timing of Seasonal Activities in Unpredictable or Constant Environments.- 6.2 Specific Functions of Circannual Timing Mechanisms.- 6.2.1 Timing and Adaptive Programming of Seasonal Activities in Hibernating Mammals.- 6.2.2 Timing and Adaptive Programming of Seasonal Activities in Migratory Birds.- 6.2.2.1 Onset of Vernal Migration.- 6.2.2.2 Onset of Autumnal Migration.- 6.2.2.3 Pattern of Autumnal Migration.- 6.2.2.4 Duration of Autumnal Migratory Activity - A Factor Determining Migratory Distance?.- 6.2.2.5 Migratory Direction.- 6.2.2.6 Photoperiodic Modification of the Program.- 6.3 Conclusions and Perspective.- Appendix. General Oscillator Model and Terminology.- References.- Systematic Index.