Magnetoreception.pptx

Presentation on non-human sense, magnetoception

1. 25/01/2022 By  Christian van der Zalm, Esmée Dragt and Radhika Joshi Magnetoreception

2. Introduction Nordmann et al., 2017, Fig. 1

3. Introduction Allows an organism to detect a magnetic field to perceive direction, altitude or location. Used for orientation and navigation Used to develop regional maps Navigation cue: the direction of the Earth’s magnetic field.

4. The Earth’s magnetic field Exists because of electric currents generated in the Earth’s core . Navigation tool: Inclination: the lines forming an angle in relation to Earth's surface. Declination: the lines forming an angle with respect to the true north. Intensity of this magnetic field: the density of the lines. Fish, turtles, birds, mammals, bacteria and insects Mouritsen , Henrik, 2015. Fig. 8

5. Three hypotheses Hypothesis 1 ( Magnetite Hypothesis) Based on a mechanically sensitive magnetite based magnetoreceptor Hypothesis 2 (Chemical Magnetoreception) Based on a light-sensitive chemical-based mechanism Hypothesis 3 (Electromagnetic Induction) Based on electromagnetic induction within accessory structures

6. The Magnetite Hypothesis Magnetic fields are detected by a mechanically sensitive magnetite-based magnetoreceptor. Bacteria and Eukaryotic Algae:  Magnetite (Fe 3 O 4 ) and Greigite (Fe 3 S 4 ) Bigger animals Magnetite Crystals

7. The Magnetite Hypothesis Bobolink Trigeminal Nerve Detects changes in magenetic field intensity Image taken from wikipedia.org

8. The Magnetite Hypothesis Rainbow Trout Use of Di-I superficial ophthalmic and trigeminal branches Movement in both anterograde and retrograde directions Posterior Entered the anterior dorsal area of the medulla oblongata Anterior Innervates skin, olfactory nerves , olfactory capsule Multilobed cells containing magnetite crystals in nose located near the basal lamina of the olfactory epithelium Mechanotransduction Image taken from wildtrout.org

9. The Chemical Magnetoreception Hypothesis Magnetic field lines as a compass , three characteristics : 1) Inclination compass: it senses the axial course of the field lines and their inclination in space. 2) It is tuned to the intensity of the magnetic field. 3) Orientation through short-wavelength light. Ultraviolet to ~565 nm green

10. The receptor molecule Photoreceptor cells in the retina of the migratory European robin contain cryptochrome Er CRY4, which binds to FAD. Warrant., 2021, Fig. 1 Cryptochrome = the only flavoprotein that can absorb photons to form radical pairs Radical pairs = a triplet or singlet depending on the spin state of the two lone electrons Antiparallel spin  radical pairs form as singlet Parallel spin  radical pairs form as triplets

11. The receptor molecule Nordmann et al., 2017, Fig. 2c Chromophore = FAD The blue/green light spectrum induces the formation of radical pairs between Cry and FAD  product further photo-reduced to form a second radical pair  influenced biochemical properties Cry  probably resulting in the activation of an unknown signaling molecule that modulates ion channel permeability.

12. Neural circuit Laterally in favour of the right eye : information is processed in the left hemisphere . Associated with the visual system. Increase in spike activity in direction sensitive cells in the nBOR and the optic tectum . Lesioning of cluster N of the Wulst caused disorientation during migration.

13. The Electromagnetic Induction Hypothesis Rays   and   Sharks :  Ampullae  of  Lorenzini Pigeons: semicircular canals Michael Winklhofer , 2019, Fig 1

14. Functional role Microorganisms   Combats   brownian motion; thermal background energy Magnetic fields at the oxygen gradient of the water (10x) Aquatic animals   Exaptation : same system, different function Magnetic fields caused by : Ocean currents Geomagnetic fields Bioelectric fields from prey Birds   Not   just navigatory , based on a magnetic map

15. Researching Magnetoreception D ifficult to locate a crystal in a thin section of tissue. Sometimes the crystals dislodge out of the tissue during cutting. Small changes; information from many cells should be received at the same time.

16. Thank you for your attention! Questions?

17. Exam question Which of the following does not act as a cue for magnetoreception? Multiple answers may be true. A. The geomagnetic field  B. The Earth's magnetic field   C. The bioelectric field of prey   D. Ocean current   E. None of the above  

18. Exam question Which of the following does not act as a cue for magnetoreception? Multiple answers may be true. A. The geomagnetic field  B. The Earth's magnetic field   C. The bioelectric field of prey   D. Ocean current   E. None of the above