[Taxacom] Surprise from a whole-genome study

[Bob Mesibov]

John,

There is no one, simple answer to your question about HGT vs convergence. I don't want to sound evasive, but each case really needs separate and careful examination.

In animals, the most careful work I've seen involves HGT to arthropods via intracellular endosymbiotic bacteria in Wolbachia. This paper

http://www.biomedcentral.com/1471-2164/10/33

is well worth reading because of its reasoning, and also because it stresses a point not often emphasised by HGT enthusiasts: transfer is not the same as expression.

It's a bit like dispersal in biogeography. It's one thing for a propagule of a plant species to disperse to a new area and germinate. It's a different matter for that plant species to establish a colony and spread out in the new area, and a different matter again for it to remain there indefinitely.

The same is probably true for HGT. Wolbachia has the potential to swap genes with its host and to carry host A genes to host B. That doesn't mean that Wolbachia genes get expressed in A, or that A genes get expressed in B. They can just sit there in the genome doing nothing, like so much of the human genome.

These genes, or pseudogenes, or 'fragments of interest' have the potential to confuse careless phylogenetic studies, but their real significance has to be thought of in evolutionary terms. If the HGT acquisitions are selected for, then they can drive evolution in the host. My gut feeling is that the vast majority of HGT acquisitions wouldn't be expressed and wouldn't be positively selected.

What's exciting in the current line of HGT research is the occasional discovery of an evolutionarily significant transfer (i.e. significant for the recipient genome, not for phylogeneticists). The nudibranch photosynthesis example is a real stunner.
-- 
Dr Robert Mesibov
Honorary Research Associate
Queen Victoria Museum and Art Gallery, and
School of Zoology, University of Tasmania
Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
Phone: (03) 64371195; 61 3 64371195