Details

Autor(en) / Beteiligte

• Peterson, Kevin J.
• Lyons, Jessica B.
• Nowak, Kristin S.
• Takacs, Carter M.
• Wargo, Matthew J.
• McPeek, Mark A.
• Davidson, Eric H.

Titel

Estimating Metazoan Divergence Times with a Molecular Clock

Ist Teil von

• Proceedings of the National Academy of Sciences - PNAS, 2004-04, Vol.101 (17), p.6536-6541

Ort / Verlag

United States: National Academy of Sciences

Erscheinungsjahr

2004

Quelle

Free E-Journal (出版社公開部分のみ）

Beschreibungen/Notizen

• Accurately dating when the first bilaterally symmetrical animals arose is crucial to our understanding of early animal evolution. The earliest unequivocally bilaterian fossils are ≈555 million years old. In contrast, molecular-clock analyses calibrated by using the fossil record of vertebrates estimate that vertebrates split from dipterans (Drosophila) ≈900 million years ago (Ma). Nonetheless, comparative genomic analyses suggest that a significant rate difference exists between vertebrates and dipterans, because the percentage difference between the genomes of mosquito and fly is greater than between fish and mouse, even though the vertebrate divergence is almost twice that of the dipteran. Here we show that the dipteran rate of molecular evolution is similar to other invertebrate taxa (echinoderms and bivalve molluscs) but not to vertebrates, which significantly decreased their rate of molecular evolution with respect to invertebrates. Using a data set consisting of the concatenation of seven different amino acid sequences from 23 in-group taxa (giving a total of 11 different invertebrate calibration points scattered throughout the bilaterian tree and across the Phanerozoic), we estimate that the last common ancestor of bilaterians arose somewhere between 573 and 656 Ma, depending on the value assigned to the parameter scaling molecular substitution rate heterogeneity. These results are in accord with the known fossil record and support the view that the Cambrian explosion reflects, in part, the diversification of bilaterian phyla.