A long time ago, on a host plant far, far away, an aphid became infected with a fungus. And then it did something unusual: it incorporated some fungal genes into its own genome.
New research by Nancy Moran and Tyler Jarvik, published yesterday in the journal Science, used the newly-published pea aphid genome to demonstrate that the genes the aphids use to make pink carotenoid pigments are derived not from insects but from a gene lineage nested well within the fungi.
This observation is interesting for two points. First, most animals with carotenoids don’t make them themselves; rather, they ingest them from other sources. Second, a gene transfer from fungus to animals?! Seriously? A lateral transfer across such great evolutionary distance is pretty rare and normally reserved for viruses.
But that’s not the real reason I’m blogging the story. The real reason is that I just happen to have a unreleased photograph of a pink pea aphid- see above. This paper is a great excuse to pull it from my archives. If you’re after more thoughtful research-blogging you can read more at Arthropoda and Not Exactly Rocket Science.
One last mystery worth mentioning, though, is why only some aphids in a population have the fungal genes. Under normal circumstances genetic drift or natural selection would either have purged the novel genes from the aphid populations or fixed them so that all individuals had them. For both green and pink forms to exist implicates some form of balancing selection. In this case, it might be because various aphid predators have different preferences.
Ladybird beetles like the red ones:
And parasitic wasps prefer green:
source: Moran & Jarvik 2010, Lateral Transfer of Genes from Fungi Underlies Carotenoid Production in Aphids. Science, doi 10.1126/science.1187113
Canon EOS 20D camera
Canon MP-E 65mm 1-5x macro lens