Migratory birds may use a magnetic compass to help
them find their way on the long seasonal journeys north, and back south.
How else might they navigate several thousand kilometer trips? What has
puzzled researchers though is how do the birds sense the reference
direction provided by the Earth's magnetic field?
Behavioural evidence and theoretical considerations have suggested that
radical-pair processes in differently oriented, light sensitive molecules
in the retina could enable migratory birds to perceive the magnetic field
as visual patterns. The cryptochromes (CRY) have been suggested as the
most likely candidate class of molecules, but do cryptochromes exist in
the retina of migratory birds?
Now, researchers in the US have shown that at least one CRY1 and one CRY2
exist in the retina of migratory garden warblers and that garden warbler
CRY1 is cytosolic. They have also revealed that gwCRY1 is concentrated in
specific cells, particularly in ganglion cells and in large displaced
ganglion cells, which also showed high levels of neuronal activity at
night when our garden warblers performed magnetic orientation.
The team has also found that there seems to be a large difference in CRY1
expression between migratory and non-migratory songbirds at night. The
difference in CRY1 expression between migrants and non-migrants is
particularly pronounced in the large displaced ganglion cells known to
project exclusively to a brain area, where scientists have found
magnetically sensitive neurons.
Consequently, cytosolic gwCRY1 might well be the primary magnetic sensory
molecule required for light-mediated magnetoreception.
Also in Issue 73 (September 2004)
P2P for scientists
Women in science
Academic poaching of researchers
Permanent implantable contact lenses
Profile of ETH Zurich
Paradoxical ozone