The colonization of land by animals: molecular phylogeny and divergence times among arthropods

Davide Pisani, Laura L Poling, Maureen Lyons-Weiler, S Blair Hedges
BMC Biology 2004, 2: 1

BACKGROUND: The earliest fossil evidence of terrestrial animal activity is from the Ordovician, approximately 450 million years ago (Ma). However, there are earlier animal fossils, and most molecular clocks suggest a deep origin of animal phyla in the Precambrian, leaving open the possibility that animals colonized land much earlier than the Ordovician. To further investigate the time of colonization of land by animals, we sequenced two nuclear genes, glyceraldehyde-3-phosphate dehydrogenase and enolase, in representative arthropods and conducted phylogenetic and molecular clock analyses of those and other available DNA and protein sequence data. To assess the robustness of animal molecular clocks, we estimated the deuterostome-arthropod divergence using the arthropod fossil record for calibration and tunicate instead of vertebrate sequences to represent Deuterostomia. Nine nuclear and 15 mitochondrial genes were used in phylogenetic analyses and 61 genes were used in molecular clock analyses.

RESULTS: Significant support was found for the unconventional pairing of myriapods (millipedes and centipedes) with chelicerates (spiders, scorpions, horseshoe crabs, etc.) using nuclear and mitochondrial genes. Our estimated time for the divergence of millipedes (Diplopoda) and centipedes (Chilopoda) was 442 +/- 50 Ma, and the divergence of insects and crustaceans was estimated as 666 +/- 58 Ma. Our results also agree with previous studies suggesting a deep divergence (approximately 1100 - 900 Ma) for arthropods and deuterostomes, considerably predating the Cambrian Explosion seen in the animal fossil record.

CONCLUSIONS: The consistent support for a close relationship between myriapods and chelicerates, using mitochondrial and nuclear genes and different methods of analysis, suggests that this unexpected result is not an artefact of analysis. We propose the name Myriochelata for this group of animals, which includes many that immobilize prey with venom. Our molecular clock analyses using arthropod fossil calibrations support earlier studies using vertebrate calibrations in finding that deuterostomes and arthropods diverged hundreds of millions of years before the Cambrian explosion. However, our molecular time estimate for the divergence of millipedes and centipedes is close to the divergence time inferred from fossils. This suggests that arthropods may have adapted to the terrestrial environment relatively late in their evolutionary history.

Full Text Links

Find Full Text Links for this Article


You are not logged in. Sign Up or Log In to join the discussion.

Related Papers

Remove bar
Read by QxMD icon Read

Save your favorite articles in one place with a free QxMD account.


Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"