Poster

         Paleobotany

A Fossil Perspective on Cenozoic Genome Size Evolution in Ginkgo

Presenting Author
Bryton Smith
Description
The fossil record complements molecular data and provides invaluable opportunities to calibrate molecular methods. The Ginkgo fossil record with its cuticles preserving cellular features provides an excellent chance to test the botany community’s understanding of neutral molecular evolution in gymnosperms. Liu et al. (2021) found that Long Terminal Repeat retrotransposons (LTR-RTs) are prevalent in Ginkgo’s repetitive DNA sequences. To estimate insertion times, they utilized the intergenic nucleotide substitution rate for Picea abies published in Nystedt et al. (2013). Liu et al. (2021) arrived at an estimate of 12-8 Ma for a time of LTR-RT proliferation in the Ginkgo genome. The fossil record is relevant to investigating such genomic topics in virtue of the strong genome size (GS)-cell size positive correlation. To investigate GS evolution in Ginkgo, we are measuring epidermal cell areas and stomatal pore lengths on cuticles spanning from the Latest Cretaceous to the present day. Our first goal is to determine whether cell size in Ginkgo has increased over the course of the Cenozoic. If cell size did increase, our next objective is to assess how the timing of the cell enlargement relates to the timeline of GS evolution and the rate of neutral molecular evolution in Ginkgo. We will also use the past cell sizes to make estimates of GS in gigabase pairs in deep time. Ultimately, we hope to evaluate whether botanists can confidently apply the substitution rate in neutral P. abies genome regions to understand the evolutionary history of other gymnosperms such as Ginkgo or whether more work is needed to refine substitution rates for specific gymnosperm taxa. References Liu, H., Wang, X., Wang, G., Cui, P., Wu, S., Ai, C., ... & Cao, F. (2021). The nearly complete genome      of Ginkgo biloba illuminates gymnosperm evolution. Nature Plants, 7(6), 748-756.       https://doi.org/10.1038/s41477-021-00933-x Nystedt, B., Street, N. R., Wetterbom, A., Zuccolo, A., Lin, Y. C., Scofield, D. G., ... & Jansson, S.       (2013). The Norway spruce genome sequence and conifer genome evolution. Nature, 497(7451),       579-584. https://doi.org/10.1038/nature12211