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Related Concept Videos

Biological Clocks and Seasonal Responses02:45

Biological Clocks and Seasonal Responses

The circadian—or biological—clock is an intrinsic, timekeeping, molecular mechanism that allows plants to coordinate physiological activities over 24-hour cycles called circadian rhythms. Photoperiodism is a collective term for the biological responses of plants to variations in the relative lengths of dark and light periods. The period of light-exposure is called the photoperiod.
Circadian Rhythms and Gene Regulation02:19

Circadian Rhythms and Gene Regulation

The biological clock is involved in many aspects of regulating complex physiology in all animals. It was in 1935 when German zoologists, Hans Kalmus and Erwin Bünning, discovered the existence of circadian rhythm in Drosophila melanogaster. However, the internal molecular mechanisms behind the circadian clock remained a mystery until 1984, when Jeffrey C. Hall, Michael Rosbash, and Michael W. Young discovered the expression of the Per gene oscillating over a 24-hour cycle. In subsequent years,...
Circadian Rhythms and Gene Regulation02:19

Circadian Rhythms and Gene Regulation

The biological clock is involved in many aspects of regulating complex physiology in all animals. It was in 1935 when German zoologists, Hans Kalmus and Erwin Bünning, discovered the existence of circadian rhythm in Drosophila melanogaster. However, the internal molecular mechanisms behind the circadian clock remained a mystery until 1984, when Jeffrey C. Hall, Michael Rosbash, and Michael W. Young discovered the expression of the Per gene oscillating over a 24-hour cycle. In subsequent years,...
The Ratio of X Chromosome to Autosomes02:45

The Ratio of X Chromosome to Autosomes

In most organisms, sex is determined by the ratio of X and Y chromosomes. However, in some organisms, such as Drosophila and C.elegans, sex is determined by the ratio of the number of X chromosomes to the number of sets of autosomes. The Y chromosome in Drosophila is active but does not determine sex. It contains genes responsible for the production of sperms in adult flies.  
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female Drosophila...
Energy Budgets00:51

Energy Budgets

Organisms must balance energy intake with the energy required for growth, maintenance and reproduction. These trade-offs result in a variety of survivorship and reproductive strategies, including semelparity and iteroparity. Semelparous species, like annual plants, have only one reproductive episode in their lifetimes and consequently have short lifespans. Iteroparous species, by contrast, have many reproductive events during their lifetimes but have relatively few offspring. These two...
Background and Environment Affect Phenotype02:27

Background and Environment Affect Phenotype

Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as temperature, oxygen availability, presence of mutagens, that can alter an organism’s phenotype.
An example of how genetic background affects phenotype can be seen in horses. The Extension gene in horses is responsible for their coat color. A wild-type gene (EE) produces black pigment in the coat, while a mutant gene (ee) produces red pigment. A...

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Related Experiment Video

Updated: May 11, 2026

Visually Sexing Loggerhead Shrike (Lanius Ludovicianus) Using Plumage Coloration and Pattern
04:10

Visually Sexing Loggerhead Shrike (Lanius Ludovicianus) Using Plumage Coloration and Pattern

Published on: March 8, 2020

Avian circannual systems: persistence and sex differences.

Sangeeta Rani1, Vinod Kumar

  • 1Department of Zoology, DST-IRHPA Center for Excellence in Biological Rhythms Research, University of Lucknow, Lucknow 226 007, India. sangeetarani7@yahoo.com

General and Comparative Endocrinology
|May 2, 2013
PubMed
Summary

Birds possess a circannual clock for seasonal timing, ensuring survival. This internal calendar synchronizes with environmental cues, though sex differences may influence breeding season timing.

Keywords:
BirdsCircannual rhythmReproductionSeasonality

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Last Updated: May 11, 2026

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Recording and Analysis of Circadian Rhythms in Running-wheel Activity in Rodents
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Area of Science:

  • * Ornithology
  • * Chronobiology
  • * Animal Physiology

Background:

  • * Birds exhibit physiological and behavioral adaptations to environmental cycles.
  • * A circannual clock system regulates seasonal events in birds, crucial for survival.
  • * This endogenous system operates with a period near 12 months, even in aperiodic conditions.

Purpose of the Study:

  • * To review information on circannual rhythms in birds.
  • * To explore the relationship between circannual rhythms and environmental cues.
  • * To highlight potential sex differences in circannual rhythmicity.

Main Methods:

  • * Review of existing literature on circannual rhythms in bird species.
  • * Analysis of studies on stonechats demonstrating long-term persistence of rhythms.
  • * Examination of synchronization with photoperiodic and non-photoperiodic cues.

Main Results:

  • * Circannual rhythms in stonechats persist for at least 12 years, indicating lifelong functionality.
  • * Circannual rhythms synchronize with environmental cues for accurate seasonal timing.
  • * Potential sex differences exist, with females possibly playing a larger role in breeding season determination.

Conclusions:

  • * Circannual timekeeping is vital for avian survival and phenotypic plasticity.
  • * The circadian clock is not involved in generating circannual rhythms.
  • * Future research should investigate the molecular mechanisms underlying circannual rhythms.