USING BIOMARKER GENOMICS TO DATE THE RISE OF COMPLEX LIFE

Molecular clocks have revolutionized how scientists organize and date the evolutionary tree of life. While molecular clocks are typically used to estimate divergence times between species, this technique can be applied to genes and gene networks as well. In this presentation, we demonstrate the utility of this approach by clarifying the evolutionary history of sterol biosynthesis, a biological pathway responsible for many of the lipid compounds that function as biomarkers in the geologic record. We discuss two projects that test contentious claims in geochemistry: (1) that biomarkers preserved in 650 million-year-old rocks provide the oldest evidence for animal life (Gold et al. 2016a,b; Gold et al. in press), and (2) that pre-Mesoproterozoic biomarkers provide evidence for early eukaryotes and aerobic metabolisms (Gold et al. 2017). Our results broadly support the utility of sterols as biomarkers, and clarify how gene duplication/transfer events have revolutionized sterol biosynthesis in sea sponges and other eukaryotes. Taken together, these projects offer a methodology to unite genetics and geochemistry in hypothesis testing.

References

Gold D.A. O’Reilly S.S., Watson J., Degnan B.M., Degnan S.M., Kroemer J., and Summons R.E. Lipidomics of the sea sponge Amphimedon queenslandica and implication for biomarker geochemistry. Geobiology. In Press.

Gold D.A., Caron A., Fournier G.P., and Summons R.E. (2017) Paleoproterozoic sterol biosynthesis and the rise of oxygen. Nature. 543(7645): 420–423.

Gold D.A., Grabenstatter J., de Mendoza A., Riesgo A., Ruiz-Trillo I., and Summons R.E. (2016a) Sterol and genomic analyses validate the sponge biomarker hypothesis. Proceedings of the National Academy of Sciences of the United States of America. 113(10): 2684–2689.

Gold D.A., O’Reilly S.S., Luo G., Briggs D.E.G., Summons R.E. (2016b) Prospects for sterane preservation in sponge fossils from museum collections, and the utility of sponge biomarkers for molecular clocks. Bulletin of the Peabody Museum of Natural History. 57(2): 181–189.