1. Avian Magnetorecption: Behavioral Tests in view of the Cryptochrome Cycle
Wolfgang Wiltschko,
Roswitha Wiltschko
J.W. Goethe-Universität,
Frankfurt a.M., Germany

2. Bird Migration: Directional tendencies during the migration season
European Robin
Erithacus rubecula
Distribution

3. Funnel paper on a light desk:
Analysis of the Avian Magnetic Compass in Behavioral Experiments with captive Birds:
Funnel cage lined with coated paper
Funnel paper on a light desk:
Funnel cage by
Emlen & Emlen (1966)

4. magnetic North turned 120° to ESE
Demonstrating
magnetic compass orientation
in robins with the help of migratory orientation:
local geomagnetic field
Control
magnetic North turned 120° to ESE
N = mN
SE = mN

5. This range is flexible, however.
Characteristics of the avian magnetic compass:
(1) Functional window :
It works only in an intensity range around the intensity where the birds live.
This range is flexible, however.
intensity in the housing room
Robins
Chickens

6. (2) Inclination compass:
Characteristics of the avian magnetic compass:
(2) Inclination compass:
Birds do not distinguish between magnetic North (»mN «) and South (»mS «), but between "poleward" (»p«) and "equatorward" (»e«)

7. Ritz, Adem & Schulten (2000) proposed :
These characteristics of the avian magnetic compass - the functional window, not using polarity - imply an unusual reception mechanism
Ritz, Adem & Schulten (2000) proposed :
Spin-chemical processes in photopigments:
Radical Pair Model

8. 'Radical Pair' model of magnetoreception
Ritz et al. (2000)
leads to response patterns on the retina, centrally symmetric to the magnetic vector
angular difference 0°
angular difference 40°

9. Effect of a Broad Band Field:
geomagnetic field: 46 µT
0.1 – 10 MHz, µT

10. Identifying a radical pair mechanism:
Radio frequency-fields applied in different orientation with respect to the static geomagnetic field: up
down

11. 7.0 MHz-field in three different alignments:up S N
down
no unspecific effect!

12. Coherence time of the radical pair: 2-10 µs
Orientation behavior at different frequencies: added vertically, intensity 480 nT
Effect of RF-field:
Coherence time of the radical pair: 2-10 µs

13. Resonance at the Larmor frequency
Effect of the RF-field added verticaly to the geomagnetic field:

14. Ritz et al. (2000) suggested:
Question:
Which photopigment forms the magnetosensitive radical pairs?
Ritz et al. (2000) suggested:
Cryptochrome
chromatophore Flavin
(from Solov‘yov et al. 2007)
Four Cryptochromes have been found in the eyes of birds:
Cry1a, Cry1b, Cry2 and Cry4

15. Immunochemical studies of the retinae of chickens and robins:
Cryptochrome 1a and UV Opsin labelled with a specific antiserum:
Chicken, Gallus gallus
Robin, Erithacus rubecula
Cryptochrome 1a found in the outer segment of the UV/V cones
UV/V cones identified as magnetoreceptors

16. Immunochemical studies in the electron-microscop:

17. Whole Mounts of the retina:
Cry1a
UV/V-opsin
Merge
Chicken,
Gallus gallus
Robin, Erithacus rubecula

18. Cryptochrome chromatophore: Flavin Absorbance of Flavin: Flavin cycle:
(after Müller and Ahmad 2011, modified)
Wavelengths to be tested
(courtesy of M. Ahmad)

19. (quantal flux about 0.8 [UV] and 8·1015 quanta / s)
Orientation of Robins tested under different wavelengths
(quantal flux about 0.8 [UV] and 8·1015 quanta / s)
424 nm
510 nm
565 nm
590 nm
635 nm
373 nm
Bird orientation requires short-wavelength light

20. The antiserum marks only light-activated Cry1a
What form of Cry1a is marked by the antiserum?
The antiserum marks only light-activated Cry1a

21. Activated Cry1a at the various wavelengths:

22. Which radical pair in the Cry-cycle mediates magnetic directional information?
We observe oriented behavior and activated Cry1a under 565 nm green light

23. Effect of pre-exposure
(1) 1 h pre-exposure under the same light as in test:
Blue, Turquoise:
1st h nd h
Green:

24. Orientation after 1 h pre-exposure under the same light as in test:
1st h
2nd h

25. Activated Cry1a at the various wavelengths:
After 30 min exposure
After 60 min exposure

26. Effect of pre-exposure
(2) Pre-exposure in total darkness for 1 h:
Cry-cycle during pre-exposure:
1 h pre-exposure, 1 h test

27. Orientation after pre-exposure in total darkness
1 h pre-exp. 1 h test
Orientation after pre-exposure in total darkness

28. Activated Cry1a at the various wavelengths:
after 30 min exposure to darkness B T G
Followed by 30 min exposure to the various colors

29. Form labelled by the antiserum
Pre-exposure experiments:
Robins are oriented under green light,
but no longer, if they have been exposed to darkness or green light before
Form labelled by the antiserum
Crucial radical pair?

30. Light and magnetic field alternatively
Effect of pulsed stimuli:
Control
light
magnetic field
Pulsed magnetic field
Light and magnetic field alternatively
Flickering light

31. Flickering light:
Pulsed magnetic field
Pulsed magnetic field and flickering light allow orientation

32. Effect of alternatively flickering light and pulsed magnetic field:
The crucial radical pair occurs in the dark!

33. Findings: Birds can still sense magnetic directions
(1) under 565 nm green light, but only if they have been in daylight before, not when they have been in green light or in the dark.
(2) in flickering light if the magnetic field is present only during the dark phase

34. Conclusion:
Not the radical pair FADH°/ Trp° is the crucial one, but probably the FADH°/O2°- generated during reoxidation

35. Thank you for your attention!
Supported by the Deutsche Forschungsgemeinschaft
Thank you for your attention!