gene expression of three cryptochromes, Cry1, Cry2 and Cry4, in the brains, muscles and eyes of zebra finches
The Lund team measured gene expression of three cryptochromes, Cry1, Cry2 and Cry4, in the brains, muscles and eyes of zebra finches. Their hypothesis was that the cryptochromes associated with magnetoreception should maintain constant reception over the circadian day.
They found that, as expected for circadian clock genes, Cry1 and Cry2 fluctuated daily - but Cry4 expressed at constant levels, making it the most likely candidate for magnetoreception.
This finding was supported by the robin study, which found the same thing.
"We also found that Cry1a, Cry1b, and Cry2 mRNA display robust circadian oscillation patterns, whereas Cry4 shows only a weak circadian oscillation," the researchers wrote.
But they made a couple of other interesting findings, too. The first is that Cry4 is clustered in a region of the retina that receives a lot of light - which makes sense for light-dependent magnetoreception.
The other is that European robins have increased Cry4 expression during the migratory season, compared to non-migratory chickens.
Both sets of researchers caution that more research is needed before Cry4 can be declared the protein responsible for magnetoreception.
The evidence is strong, but it's not definitive, and both Cry1 and Cry2 have also been implicated in magnetoreception, the former in garden warblers and the latter in fruit flies .
Observing birds with non-functioning Cry4 could help confirm the role it seems to play, while other studies will be needed to figure Cry1's role.
This is how a bird might see magnetic fields. ( Theoretical and Computational Biophysics/UofI )
So what does a bird actually see? Well, we can't ever know what the world looks like through another species' eyes, but we can take a very strong guess.
