moa feathers & DNA – an example of reductionism

 Now, here’s a misleading sentence for you: The giant moa has been "rebuilt" by scientists using DNA from prehistoric feathers, revealing the true colours of the extinct bird. It’s from a news story in the Dominion Post, although I first read it in the Herald. At the time I thought this would be a good topic for a blog, & I’ve been spurred to write one following a discussion I had today at this conference. (This one’s for you, Rose!)

What’s my problem with this story? Well, it makes it sound as if the scientists involved in this particular project had been able to determine feather colour by sequencing DNA from moa remains. And that’s actually why I used the word ‘reductionism’ in the title – because the news article is basically saying, we have the genes, so now we know everything about this species. But this is a very long way indeed from the real state of play. (And as I’m sure you realise, individual genes are simply one part of a larger, complex, system. So many factors – both environmental & intrinsic to the organism – can affect gene expression that it would be hard to say with certainty that a particular gene would definitively produce a particular feather colour.)

What did happen is that the research team studied moa feathers from three different sites in Central Otago (Rawlence et al 2009). They were able to obtain DNA sequences from the feathers associated with the bones, which is rather neat in itself as feathers tend to degrade rather more quickly than bones.  In addition, they were able to demonstrate that mtDNA was present in all parts of the structure (calanus, rachis, barbs, barbules & barbicels) of both modern & ancient feathers – this is a significant advance as previously scientists had believed that you’d only be able to obtain DNA from the calanus, at the base of the feather (the part that’s actually embedded in the bird’s flesh).

Using the feather mtDNA the team was able to match feathers with particular species, including  the stout-legged moa, heavy-footed moa, upland moa and South Island giant moa. This was possible because previous research projects had identified mtDNA control region sequences belonging to particular moa species. And because the feathers, although faded, hadn’t completely lost their colour, the researchers were able to draw some conclusions about the colour patterns of the different birds. For example, some white-tipped feathers were traced to the heavy footed moa (Pachyornis elephantopus), and a comparison of these feathers to those of large modern birds suggests that Pachyornis plumage was like that of one of our kiwi species.

A nice detective story, but most definitely not as described in the press 🙂

(And there wasn’t too much disruption to normal service, after all!)

N.J.Rawlence, J.R.Wood, K.N.Armstrong & A.Cooper (2009 – in press) DNA content and distribution in ancient feathers and potential to reconstruct the plumage of extince avian taxa. Proceedings of the Royal Society B, doi:10.1090/rspb.2009.0755