Friday, January 27, 2006

Big botany

Two papers on plants caught my eye this week. The first is from Nature on the scaling of plant metabolic rate. Peter Reich and his colleagues say that plant respiration increases linearly with plant size — that is, a plant has a metabolic rate twice that of one half its size.

This seems to contradict the West, Brown and Enquist (WBE) model of metabolic rate, which says that metabolic rate in all organisms is proportional to the 3/4 power of body mass — so a plant would have a metabolic rate only about 1.7 times that of one half its size.

Whether this is true, and whether the WBE model is the right way to explain metabolic rate, is controversial. I think that there is good evidence for what's known as quarter-power scaling over a wide range of plants and animals, and I also think that the WBE model makes a lot of sense (but then I've written a book about all this, so I would say that). But these things take decades to sort out, so there will be a lot of to-ing and fro-ing between both sides before any hard consensus emerges. Don't expect the quarter-power people to give up their ideas in the face of this new evidence.

The other paper deals with another big issue in ecology — what maintains the high diversity in tropical forests? Writing in Science, a massive team of ecologists led by Christopher Wills present evidence from forest plots in Panama and Malaysia showing that rare species are more likely to survive than common ones — an advantage that buffers against extinction.

The team don't seem to plump for a reason as to why this should be. One possibility is the Janzen-Connell hypothesis, which says that mature trees attract pathogens, herbivores and so on that make it harder for seeds of the same species to germinate in the vicinity. Another possibility stems from the fact that all species compete most strongly with other members of their own kind — because their needs are so similar — than with other species, and that this competition is weaker for rare species.

I am reading Jonathon Silvertown's new book on plant ecology, Demons in Eden at the mo. He has an excellent discussion of these issues that comes down in favour of the J-C view of things. I don't think things are as clear cut as all that, but there does seem to be good evidence that the process is important in forests.

Darwin, Homer and Austen

I've got a piece in this week's Nature called "Textual selection" that looks at the newish field of Darwinian literary theory (registration required — see here for a summary). These guys (mostly) want to chuck out Freud, Marx et al, and interpret texts from a Darwinian perspective — mate choice, kin selection and all that. It was interesting speaking to non-scientists (including the author Ian McEwan), and try to get my head around someone else's issues and arguments for a change.

These folk think like scientists — they want to make testable hypotheses, collect data, get robust answers, move on. This is very different to a lot of literary criticism, which is also about kicking ideas around, as kicking them out. Many literary critics seem to read Freud, or Marx or Derrida, as if it was a novel, rather than anything with a claim to objective truth — whether an idea is stimulating is as important as whether it is true.

This has got a bit of coverage recently. For more, try here, and here to read Mark Lawson slagging whole idea off in the Guardian. The NY times also had a big piece, but it seems to be subscriber-only now.

Thursday, January 12, 2006

Did viruses invent DNA?

What with the threat of bird flu, the reality of HIV, and the general unseemliness of having one's cells pressed into labour on behalf of something alien and microscopic, it is small wonder that people don't much like viruses. But it's possible that we may actually have something to thank the little parasites for. They may have been the first creatures to find a use for DNA, a discovery that set life on the road to its current rich complexity...

This feature in Nature (by me; registration required) looks at Patrick Forterre's idea that viruses invented DNA as a way of invading cells in the RNA world — just as many viruses today use similar genetic tricks to evade cellular defences. It's a neat idea, and raises the useful question of what the original advantage of DNA might have been. It is more chemically stable than RNA (which biologists think came first) and can be used for longer genomes.

But, Forterre points out, no cell could know that it wanted a longer, more complex genome and evolve DNA accordingly, because evolution has no foresight. Not everyone agrees, but there is a lot of excitement about viral diversity and evolution at the moment - there's some crazy stuff out there, virus-wise, much of it currently being discovered by David Prangishvili.