How the Aphid got its Pink

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A pleasingly pink pea aphid (Acrythosiphon pisum)

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:

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And parasitic wasps prefer green:

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source: Moran & Jarvik 2010, Lateral Transfer of Genes from Fungi Underlies Carotenoid Production in Aphids. Science, doi 10.1126/science.1187113


photo details:
Canon EOS 20D camera
Canon MP-E 65mm 1-5x macro lens

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...And then it did something unusual:

Lateral gene transfer is unusual? Here I was thinking that evolution is rather reticulate and that calling a phylogram a "tree" is rather unfortunate terminology since actual tree branches don't tend to anastomize. But what do I know, I'm just a eukaryote?

By darwinsdog (not verified) on 30 Apr 2010 #permalink

But what's so important about pink or red or green to aphid predators? I just don't see why, unless the red, green, or pink aphids each have another factor associated with each color, and these factors attract/repel one or both predators.

Difference between cherry and lime--which lifesavers do you prefer? Seriously, there could be a flavor or visual cue difference in what is apparent to each predator/parasitoid. Red is often aposomatic and tied to something that needs to be overcome, but in this case is more apparent to the predator than green=plant. On the other hand, perhaps choosing the green ones is a more successful strategy for parasitoids as they (and thus parasitoid progeny) are less likely to be eaten by ladybird beetles.

ok maybe aphids aren't so bad sometimes... now i need to screen my aphids for this gene!

By ihateaphids (not verified) on 30 Apr 2010 #permalink

also, sir, unless it's a trick o' the light, your wasp appears to be ovipositing in a pink aphid :)

By ihateaphids (not verified) on 30 Apr 2010 #permalink

I assume that ladybirds sequester at least some of their carotenoids from the aphids that they eat? That might explain their preference for strawberry- and cherry-flavored aphids...

Really nice photo of the Aphid. Nice fullish depth of field for something that small. Nice simple thing, pleasing pastel colors. Diagonal elements. That is a killer photo.

By Josh Lewis (not verified) on 30 Apr 2010 #permalink

Well, the photo might be even better if it wasn't cut off at the edges on every side: one or two sides would do, but top, bottom, left, and right cramps the poor insect.

Love the aphid photo.

Little more snarkiness over here at ScienceBlogs compared to WordPress, eh Alex! If anyone can deal with it, you can :)

Apparently bugs have a history of horizontal gene transfer.

Lateral gene transfer turns up just about everywhere one looks for it. The notion that it's rare or "unusual" is simply an artifact of it's not having been looked for or recognized by previous generations of biologists.

By darwinsdog (not verified) on 03 May 2010 #permalink

Darwinsdog-

I dunno. In your genome, how many of your genes were acquired de novo by lateral transfer? And how many did you inherit vertically from your parents?

Nice combination of pictures and a reference. That combination certainly warrants some reading time this weekend. Thanks for posting!