Estimating the timing of early eukaryotic diversification with multigene molecular clocks
Laura Wegener Parfreya,b,2, Daniel J. G. Lahra,b, Andrew H. Knollc,1, and Laura A. Katza,b,1
Author Affiliations
aProgram in Organismic and Evolutionary Biology, University of Massachusetts, Amherst, MA 01003;
bDepartment of Biological Sciences, Smith College, Northampton, MA 01063; and
cDepartment of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138
Contributed by Andrew H. Knoll, July 1, 2011 (sent for review February 9, 2011)
Abstract
Although macroscopic plants, animals, and fungi are the most familiar eukaryotes, the bulk of eukaryotic diversity is microbial. Elucidating the timing of diversification among the more than 70 lineages is key to understanding the evolution of eukaryotes. Here, we use taxon-rich multigene data combined with diverse fossils and a relaxed molecular clock framework to estimate the timing of the last common ancestor of extant eukaryotes and the divergence of major clades. Overall, these analyses suggest that the last common ancestor lived between 1866 and 1679 Ma, consistent with the earliest microfossils interpreted with confidence as eukaryotic. During this interval, the Earth's surface differed markedly from today; for example, the oceans were incompletely ventilated, with ferruginous and, after about 1800 Ma, sulfidic water masses commonly lying beneath moderately oxygenated surface waters. Our time estimates also indicate that the major clades of eukaryotes diverged before 1000 Ma, with most or all probably diverging before 1200 Ma. Fossils, however, suggest that diversity within major extant clades expanded later, beginning about 800 Ma, when the oceans began their transition to a more modern chemical state. In combination, paleontological and molecular approaches indicate that long stems preceded diversification in the major eukaryotic lineages.
microbial eukaryotes, Proterozoic oceans, taxon sampling, origin of eukaryotes
Footnotes
1To whom correspondence may be addressed.
E-mail:aknoll@oeb.harvard.edu or lkatz@smith.edu
2 Present address: Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309.
Author contributions: L.W.P. and L.A.K. designed research; L.W.P. and D.J.G.L. performed research; L.W.P., D.J.G.L., A.H.K., and L.A.K. analyzed data; and L.W.P., D.J.G.L., A.H.K., and L.A.K. wrote the paper.
The authors declare no conflict of interest.
This article contains supporting information online at
Freely available online through the PNAS open access option.
