Question

Question 3: Biological Clocks and Navigation .Describe the physiological basis of circadian rhythms and the mechanisms by which birds navigate during migration. Include in your answer: a. a description of circadian rhythms and zugunruhe b. a description of the molecular and physiological mechanisms for entraining circadian rhythms and the timing of seasonal movements in birds c. a description of the current hypothesis for bird navigation using Earth’s magnetic field

Please Write 500 words atleast for the 4 parts in total kindly.

Answer 1

A.When birds are placed in a round cage at night, they show migratory restlessness or Zugunruhe .The birds primarily jump/flutter in their migratory direction, and when the magnetic field is turned horizontally in the absence of celestial cues, the birds turn their orientation with the magnetic field .

This is the behavioral evidence required to show that a migratory bird species possesses and is able to use a magnetic compass .A magnetic compass has been found in more or less every migratory bird species , therefore, it is quite safe to presume that all migratory birds and potentially birds in general possess a magnetic compass.the magnetic compass of night-migratory birds does not separate between North and South like our ship compass, but it distinguishes between “toward the magnetic equator” and “toward the magnetic pole” (the Magnetic North Pole in the Northern Hemisphere and the Magnetic South Pole in the Southern Hemisphere).

the birds’ magnetic compass sense have narrow functional intensity window, but this window seems to be extendable to new intensities after a few hours of adaptation to a changed magnetic field intensity .Seasonal and circadian rhythms of melatonin have been associated with this migratory nocturnal restlessness or 'zugunruhe'. Zugunruhe refers to nocturnal migratory restless. However, during migration, melatonin levels at night are lower than nonmigratory, nightly melatonin levels.In migratory birds, endogenous daily (circadian) and annual (circannual) rhythms serve as biological clocks that provide the major basis for their temporal orientation. Circannual rhythms are responsible for the initiation of migration both in autumn and spring. This function of timing migrations is particularly important for birds that spend the winter close to the equator where the environment is too constant or irregular to provide accurate timing cues. In addition, circannual rhythms produce programmes that determine both the temporal and the spatial course of migration. In normally day-active but nocturnally migrating birds, circannual signals cause alterations in the circadian system leading to the development of nocturnal activity,there is evidence that changes in the diurnal pattern of melatonin secretion by the pineal gland are associated with, and possibly causally involved in, the waxing and waning of nocturnal activity. These changes in the melatonin pattern presumably also affect general synchronization properties of the circadian system to Zeitgebers in such a way that circadian rhythms adjust faster to new conditions after long transmeridian flights.

B.Avian behavior and physiology are embedded in time at many levels of biological organization. Biological clock function in birds is critical for sleep/wake cycles, but may also regulate the acquisition of place memory, learning of song ,social integration, and time-compensated navigation.

This relationship has two major implications. First, mechanisms of the circadian clock should be linked in some way to the mechanisms of all these behaviors.the molecular, physiological, and behavioral elements of the circadian system would place birds at a very interesting fulcrum in the neurobiology of time in learning, memory, and navigation.

The avian circadian system is a complex of mutually coupled pacemakers residing in the pineal gland, retinae, and the avian homologs of the suprachiasmatic nucleus (SCN), synchronized to environmental light cycles (LD) by photoreceptors in the eye, pineal gland, and multiple sites within the brain . At the molecular level, genomic and transcriptional analyses have identified a highly conserved network of “clock genes” that are orthologous to clock genes identified in insects and mammals.The seasonal migration cycle involves journeys that exceed tens of thousands of miles or kilometers in length. A migration route can involve resting and refueling stops, although some species complete their migration non-stop.
Climate change can affect seasonal migration. Bird migration has been affected for species whose route takes them over deserts. In highly developed areas of the world, light pollution can also pose problems for birds who migrate at night and use the moon and stars for navigation.

C.Birds use Earth's magnetic field as sort of a heads-up display to help them navigate the globe. The Earth's magnetic field is a result of the movement or convection of liquid iron in the outer core. As the liquid metal in the outer core moves, it generates electric currents, which lead to a magnetic field.

Earth's magnetic field plays a vital role in animal migration . Birds use Earth's magnetic field as sort of a heads-up display to help them navigate the globe.

The Earth's magnetic field is a result of the movement or convection of liquid iron in the outer core. As the liquid metal in the outer core moves, it generates electric currents, which lead to a magnetic field. The continual movement of liquid metal through this magnetic field creates stronger electrical currents and thus a stronger magnetic field. This positive feedback loop is called the geomagnetic dynamo.

A particular type of cryptochrome protein in birds’ retinas known as Cry4, which is sensitive to blue light—including that given off by the Earth’s magnetic field. Both plants and animals are known to contain photoreceptive cells that respond to blue light, which are necessary for circadian rhythms.

A bird’s visual magnetic detection cells rely on quantum coherence. It’s interactions with the quantum field that allows migratory birds to navigate, three possible cryptochromes, Cry1, Cry2, and Cry 4, may be involved.