Zebrafish Temperature Selection and Synchronization of Locomotor Activity Circadian Rhythm to Ahemeral Cycles of Light and Temperature

Feb 13, 2009Chronobiology international

Zebrafish choose temperatures and align their daily movement patterns to combined light and temperature cycles

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Abstract

78% of zebrafish synchronized their activity rhythms to a 24:20 degrees C thermocycle in the absence of light.

Both light and temperature cycles are significant factors that synchronize zebrafish activity rhythms.
When given a choice, most zebrafish preferred the higher temperature of 24 degrees C and exhibited daytime activity.
A small group (25%) of zebrafish that chose the lower temperature of 20 degrees C displayed nighttime activity.
Under conflicting light and temperature cycles, zebrafish maintained diurnal activity, especially around dawn and dusk.
Zebrafish primarily synchronized to light cycles when subjected to ahemeral cycles of light and temperature, indicating a stronger influence of light.
Despite the dominance of light as a synchronizer, temperature cycles can still influence circadian rhythms.

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In addition to light cycles, temperature cycles are among the most important synchronizers in nature. Indeed, both clock gene expression and circadian activity rhythms entrain to thermocycles. This study aimed to extend our knowledge of the relative strength of light and temperature as zeitgebers for zebrafish locomotor activity rhythms. When the capacity of a 24:20 degrees C (thermophase:cryophase, referred to as TC) thermocycle to synchronize activity rhythms under LL was evaluated, it was found that most groups (78%) synchronized to these conditions. Under LD, when zebrafish were allowed to select the water temperature (24 degrees C vs. 20 degrees C), most fish selected the higher temperature and showed diurnal activity, while a small (25%) percentage of fish that preferred the lower temperature displayed nocturnal activity. Under conflicting LD and TC cycles, fish showed diurnal activity when the zeitgebers were in phase or in antiphase, with a high percentage of activity displayed around dawn and dusk (22% and 34% of the total activity for LD/TC and LD/CT, respectively). Finally, to test the relative strength of each zeitgeber, fish were subjected to ahemeral cycles of light (T=25 h) and temperature (T=23 h). Zebrafish synchronized mostly to the light cycle, although they displayed relative coordination, as their locomotor activity increased when light and thermophase coincided. These findings show that although light is a stronger synchronizer than temperature, TC cycles alone can entrain circadian rhythms and interfere in their light synchronization, suggesting the existence of both light- and temperature-entrainable oscillators that are weakly coupled.

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Zebrafish Temperature Selection and Synchronization of Locomotor Activity Circadian Rhythm to Ahemeral Cycles of Light and Temperature

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