HR: 1340h
AN: B33B-0256    [Abstracts]
TI: Molecular Fossils as Time Indicators for the Evolution of Diatoms.
AU: * Rampen, S W
EM: rampen@nioz.nl
AF: Department of Marine Biogeochemistry and Toxicology, Royal Netherlands Institute for Sea Research, Landsdiep 4 P.O. Box 59, Den Burg (Texel), NL-1790 AB Netherlands
AU: Schouten, S
EM: schouten@nioz.nl
AF: Department of Marine Biogeochemistry and Toxicology, Royal Netherlands Institute for Sea Research, Landsdiep 4 P.O. Box 59, Den Burg (Texel), NL-1790 AB Netherlands
AU: Muyzer, G
EM: g.muyzer@tnw.tudelft.nl
AF: Department of Biotechnology, Environmental Biotechnology Group, Delft University of Technology, Julianalaan 67, Delft, 2628 BC Netherlands
AU: Abbas, B
EM: abbas@nioz.nl
AF: Department of Marine Biogeochemistry and Toxicology, Royal Netherlands Institute for Sea Research, Landsdiep 4 P.O. Box 59, Den Burg (Texel), NL-1790 AB Netherlands
AU: Rowland, S J
EM: srowland@plymouth.ac.uk
AF: Petroleum and Environmental Geochemistry Group, School of Earth, Ocean and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, PL4 8AA United Kingdom
AU: Moldowan, M
EM: moldowan@pangea.stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Green Earth Science Bldg 201, Stanford, CA 94305-2115 United States
AU: Sinninghe Damst\'{e}, J S
EM: damste@nioz.nl
AF: Department of Marine Biogeochemistry and Toxicology, Royal Netherlands Institute for Sea Research, Landsdiep 4 P.O. Box 59, Den Burg (Texel), NL-1790 AB Netherlands
AB: Bacillariophyta (diatoms) are one of the most abundant divisions of phytoplankton, and contribute to almost 50% of the primary productivity of today's oceans. However, their ecological dominance is relatively young and little is known about the exact pace of their rapid evolution. DNA analyses on diatoms and the use of molecular clock calculations can help to reconstruct their evolution, but this molecular clock rate needs to be calibrated against the fossil record to determine the mutation rate. Until now, diatom silica skeletons have been used for reconstructing the evolution of diatoms, but their use is limited due to destruction by diagenesis. Molecular fossils may prove to be more useful for time reconstruction. To search for suitable compounds, we have analyzed both the lipid composition and 18S rRNA sequences of ca. 100 marine diatoms. This revealed that some specific phylogenetic clusters within the diatoms produce specific organic compounds, so-called diatom biomarkers. One group of diatom biomarkers are the C$_{25}$ highly branched isoprenoid (HBI) alkenes (1,2). HBI biosynthesis evolved independently at least twice in the diatoms. The first group of HBI producers consists of the centric diatoms of the genus {\it Rhizosolenia}, the second group comprises pennate diatoms of the genera {\it Haslea}, {\it Navicula} and {\it Pleurosigma}. Based on the constructed phylogenetic tree it is likely that the HBI biosynthesis evolved first in the older group of centric diatoms (i.e. the {\it Rhizosolenia} genus). The fossil record was studied to determine the geological occurrence of C$_{25}$ HBI alkenes, and this data set shows that HBI biosynthesis evolved ca. 91.5 My ago, so we can date the evolution of the genus {\it Rizosolenia} to ca. 91.5 My. With this information, we can now accurately predict the mutation rate of the 18S rDNA gene to 1% per 14.8 My for {\it Rhizosolenia}, which is substantially faster than the 1% per 18-26 My reported previously for diatoms in general. Another specific biomarker is 24-norsterol. Its value as an age diagnostic biomarker was already reported (3), but the source of this sterol was still unknown although a diatomaceous source was assumed. We have now found this sterol in the diatom species {\it Thalassiosira aff. Antarctica}. In combination with the knowledge that the 24-norsterol production increased substantially during the Cretaceous this may provide a tool to predict the mutation rate of the Thalassiosirales. Our data show that molecular paleontology can assist in obtaining more reliable estimates of the molecular clock rate and thus be an important tool in reconstructing the evolution of diatoms. References: 1. J.K. Volkman et al., Org.Geochem. 21, 407-413 (1994). 2. J.S. Sinninghe Damst‚ et al., Science 304, 584-587 (2004). 3. A.G. Holba et al., Org.Geochem. 29, 1269-1283 (1998).
DE: 4840 Microbiology
DE: 4855 Plankton
DE: 1050 Marine geochemistry (4835, 4850)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting