Thursday, February 16, 2012

EOL Phylogenetic Tree Challenge

34106 130 130The Encyclopedia of Life have announced the EOL Phylogenetic Tree Challenge. The contest has two purposes:

It provides a testbed for the Evolutionary Informatics community to develop robust methods for producing, serving, and evaluating large, biologically meaningful trees that will be useful both to the research community and to broader audiences.

It enables the Encyclopedia of Life to organise the information it aggregates according to phylogenetic relationships; in other words, it provides a direct pipeline from research results to practical use.

First prize is a trip to iEvoBio 2012, this year in Ottawa, Canada. For more details visit the challenge website. There is also an EOL community devoted to this challenge.

Challenges are great things, especially ones with worthwhile tasks and decent prizes. EOL badly needs a phylogenetic perspective, so this is a welcome development.

But (there's always a but), I can't help feeling that we need something a little more radical. The tree of life isn't a tree. At deep levels it's a forest, and even at shallow levels things are a complicated tangle of gene trees. Sometimes the tree is clear, sometimes not, and some of this is real and some reflects our ignorance.

If you want a simple tree to navigate, then I'd argue that the NCBI tree is a pretty good start, and EOL already has this. What would be really cool is to have a way to navigate that makes it clear that phylogenetic knowledge has a degree of uncertainty, and that the "tree of life" might be better depicted as a set of overlapping trees. The mental image I have is of a collage of trees from different data sets, superimposed over each other, with perhaps an underlying consensus to help navigate. This visualisation could be zoomable, because in some ways the tree of life is fractal. Trees don't stop at species, as the wealth of barcoding and phylogeographic studies show. Given computational constraints (not to mention visualisation issues), I wonder whether there is an effective limit to the size of any one tree in terms of number of taxa. What varies is the taxonomic scope. So we could imagine a backbone tree based on slowly evolving genes, we zoom in and more trees appear, but at lower levels, and finally we hit populations and individuals, trees that may have 100's of samples, but a very narrow scope.

This is all rather poorly articulated, but I can't help wondering whether a phylogenetic classification will end up distorting the very thing we're trying to depict. It also looses connection with the underlying data (and trees), which for me is a huge drawback of existing classifications. There's no sense of why they are the way they are. There's a chance here to bring together ideas that have been kicking around in the phylogenetic community for a couple of decades and rethink how we navigate the "tree of life".