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Cassie Wesseln

Cassie Wesseln

Research Overview

I am interested in investigating the evolutionary history and palaeoecology of grasslands with the fossil pollen record. Pollen is often diagnostic of the parent plant to the genus or even species level, and it is very well-preserved and abundant in the fossil record. However, within the grass family (Poaceae), pollen morphology is uniform and this therefore prevents taxonomic identification of grasses below the family level. This poor resolution of taxonomy via pollen within Poaceae currently impedes our ability to use the abundant, well-preserved fossil grass pollen record to understand patterns of Poaceae diversification and species level response to palaeoenvironmental change. The first two chapters of my PhD encompass the development of super resolution and high contrast microscopy techniques to recover taxonomically important grass pollen morphology that can later be quantitatively analyzed to assign species and genus level taxonomic identifications to modern grasses. The third and fourth chapters of my PhD will be applications of the techniques developed in Chapters 1-2 to fossil grass pollen records that span the Pliocene-Miocene when grasslands first developed as a dominant biome on Earth.

We can learn so much about ancient grasslands if we look at fossil grass pollen records, but first we have to find a way to visualize pollen morphology better so that we can in turn improve our classification of the parent grass from the grass pollen grain. Knowing what grasses went extinct, originated, became more dominant or sparse as well as the timing of grass family diversification throughout millions of years of palaeoenvironmental change is critical to augmenting our understanding of this biome’s response to such analogous change that is happening today and will continue to happen in the future.

Cassie WesslnHere I am removing flowers from herbarium grass specimens so that I can chemically process them and isolate the grass pollen. Then I can mount the pollen on microscope slides and capture its morphology using super resolution and high contrast microscopy techniques. After the images are collected, I work with my collaborators on quantifying the taxonomically important morphology of each species to ultimately differentiate among grass genera and species.

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