Hi James, I'm not sure whether anyone else is reading the message board but this paper on the phylogenetic relationship between coelacanths to other fish might interest you.

Arnason U, Gullberg A, Janke A, Joss J & Elmerot C (2004) "Mitogenomic analyses of deep gnathostome divergences: a fish is a fish" Gene 333: 61-70

Despite the obtuse title the paper is highly relevant to the Coelacanth program, especially to the genome resource and education / communication initiatives, as the relationship between coelacanths and our lineage has been used as a justification for the program.

The authors have assembled an impressive dataset of DNA sequences to address an old chestnut - which are the closest living relatives of land-vertebrates? Many of the living candidates assumed their current forms at some time in the Mesozoic (after 250 million years ago), and their progenitor lineages seem to have diverged over a relatively short period around 420 mya, so the fossil record is tolerant of alternate hypotheses.

Most studies have perceived this as a question of whether lungfish or the coelacanth is more closely related to the lineage leading to humans. These previous studies used other fish (actinopterygii) as outgroups, to frame their reconstruction of evolutionary history. This in turn depends on a belief that cartilagenous fishes (sharks and rays) arose as an early branch, prior to a split between ray-finned and lobe-finned fishes (with the latter leading to tetrapods, the land vertebrates).

Arnason and collegues delve deeper and include data from lampreys to frame the history all jawed vertebrates (gnathostomes). Their analyses of entire mitochondrial genomes, and of some data from nuclear ribosomal genes, suggest that these received wisdoms are actually incorrect. Their data provide strong evidence that the fundamental split in jawed vertebrates is between the lineage leading to land vertebrates and that leading to all living fishes - whether cartilagenous, lobe-finned or ray-finned, hence "a fish is a fish"... and a tetrapod is not.

The relationships among the major lineages of fishes, such as that between lungfishes and coelacanths, are not resolved, with the exception that cladistians (bichir and ropefish) were found to be a sister group to all other fishes, including cartilagenous fishes.

This finding requires confirmation from many more independent genes but if these results hold it would down-weight the priority given to the coelacanth in terms of understanding our own origins. Instead of being a single sister, or near sister, to tetrapods, the coelacanth would appear to be one of five major lineages of fish, which together form our sister lineage. Sequencing a coelacanth genome is still an important goal, as it will help us to understand how vertebrate bodies are built and regulated. The value of a coelacanth genome resource would shift, however, from an understanding of our own lineage, to the reconstruction of the ancestral fish genome, which would then be compared with our own. Seen from this perspective the coelacanth has equal priority with sharks and lungfish in the genome market, and somewhat less than that of bichir. A recent paper on bichir Hox genes, Chiu et al. 2004 Genome Research 14:11-17, shows how this could work (The Hox genes were similarly proposed as the target sequence region for the Coelacanth genome resource initiative).

I'll post you pdfs of these papers which you might be able to make available through the site.

-- Michael Cunningham (cunninghammj@qwa.uovs.ac.za), November 18, 2004

Answers

Thanks Michael! I have uploaded the documents to the website. They're available at http://www.coelacanth.ac.za/project_science/genome_resources/useful_documents/index.html

-- James Stapley (james@jamesstapley.com), December 07, 2004.