Light-dependent magnetoreception in birds: increasing intensity of monochromatic light changes the nature of the response - PubMed (original) (raw)

Light-dependent magnetoreception in birds: increasing intensity of monochromatic light changes the nature of the response

Roswitha Wiltschko et al. Front Zool. 2007.

Abstract

Background: The Radical Pair model proposes that magnetoreception is a light-dependent process. Under low monochromatic light from the short-wavelength part of the visual spectrum, migratory birds show orientation in their migratory direction. Under monochromatic light of higher intensity, however, they showed unusual preferences for other directions or axial preferences. To determine whether or not these responses are still controlled by the respective light regimes, European robins, Erithacus rubecula, were tested under UV, Blue, Turquoise and Green light at increasing intensities, with orientation in migratory direction serving as a criterion whether or not magnetoreception works in the normal way.

Results: The birds were well oriented in their seasonally appropriate migratory direction under 424 nm Blue, 502 nm Turquoise and 565 nm Green light of low intensity with a quantal flux of 8 x 10(15) quanta s(-1) m(-2), indicating unimpaired magnetoreception. Under 373 nm UV of the same quantal flux, they were not oriented in migratory direction, showing a preference for the east-west axis instead, but they were well oriented in migratory direction under UV of lower intensity. Intensities of above 36 x 10(15) quanta s(-1) m(-2) of Blue, Turquoise and Green light elicited a variety of responses: disorientation, headings along the east-west axis, headings along the north-south axis or 'fixed' direction tendencies. These responses changed as the intensity was increased from 36 x 10(15) quanta s(-1) m(-2) to 54 and 72 x 10(15) quanta s(-1) m(-2).

Conclusion: The specific manifestation of responses in directions other than the migratory direction clearly depends on the ambient light regime. This implies that even when the mechanisms normally providing magnetic compass information seem disrupted, processes that are activated by light still control the behavior. It suggests complex interactions between different types of receptors, magnetic and visual. The nature of the receptors involved and details of their connections are not yet known; however, a role of the color cones in the processes mediating magnetic input is suggested.

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Figures

Figure 1

Figure 1

Orientation of European robins under 424 nm Blue, 502 nm Turquoise and 565 nm Green light of different quantal flux (given on the left side in quanta s-1m-2). The triangles at the periphery of the circles mark the mean headings of individual birds, with solid symbols indicating unimodal means and open symbols indicating the preferred end of mean axes (see text). The arrows and double arrows represent the grand mean vectors and grand mean axes, respectively, with the two inner circles marking the 5% (dotted) and 1% significance border of the Rayleigh test [47].

Figure 2

Figure 2

Orientation of European robins under 373 nm UV light of different quantal flux (in quanta s-1m-2 above the circle). Symbols as in figure 1.

Figure 3

Figure 3

Test apparatus for testing individual birds under monochromatic lights.

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