My research focuses on elucidating the evolutionary history of one of the most important groups of plants alive today, grasses (family Poaceae). Grass-dominated ecosystems now occupy 40% of Earth’s land surface, but likely only emerged in the last ~30 million years, reshaping ecosystems across all continents. To shed light on this remarkable ecological transformation, I use a lesser known type of plant fossil, namely fossilized plant silica (“phytoliths”). Phytoliths form inside and around cells in living plants and can be preserved in the soil after plant tissues decay. Much has been learned, through phytolith studies, about when and where grasses and grasslands first emerge. However, many crucial questions remain that cannot be answered using current ways of interpreting which type of grass each fossil phytolith represents. These methods suffer from being subjective and inexact, resulting in interpretations of how grasses evolved and the composition of ancient grass communities that are at best vague and at worst erroneous.

In this CAREER project, postdoc Tim Gallaher and I, and a large and diverse group of primarily undergraduate students worked to significantly enhance the ability of phytoliths to reconstruct grass lineages and ecology through time. We did so by studying in detail the three-dimensional (3D) shape (and size) of grass phytoliths. Specifically, we designed a protocol for imaging phytoliths from nearly 200 species of species within Poaceae in 3D and converting the images to 3D phytolith models. The shape and size of these 3D models could then be measured and compared (using a method called 3D geometric morphometrics), allowing us to study how the shape and size of grass phytoliths have evolved within the grass family (Poaceae). More importantly, this method makes it possible to compare unknown fossil grass phytoliths to our database and determine with good precision which group of grasses that produced it.

Using this new identification “tool”, we can now answer questions about where and when grasses evolved and diversified, what the earliest grass communities looked like, and study differences in grassland evolution on different continents. For this grant, we have focused on understanding the ecology of some of the earliest grasses that lived ~60 million years ago in Argentina, South America. This work is still underway but preliminary data indicate that they lived in the forest understory or forest margins. We are also studying grasses that were present as Great Plains of North America and Turkey transformed from forests to grass-dominated habitats.

This grant also funded investigation into if the high levels of silica (in the form of phytoliths) deposited in the leaves of living grasses evolved as an adaptation to deterring grazers that emerged as grasslands spread. We found that high silica concentrations most likely did not evolve to deter herbivory on grasses, but instead that high silica levels occur in response to climatic conditions where the grasses grow.

This grant also funded several education and outreach efforts through both UW Biology and the Burke Museum of Natural History and Culture. First, I redesigned my upper-level paleobotany and paleoecology class (Greening of the Earth) to include evidence-based learning and hands-on activities, such as a quarter-long research project on fossils that the students themselves collected on a local field trip to a fossil site. Second, my graduate students and I worked with Burke Museum Education staff to design a free afterschool STEM program for middle-school girls (“Girls in Science”). In this program, 16 girls from diverse backgrounds meet women researchers (faculty, graduate students) once a month during the academic year to do hands-on STEM research activities. This program, which has gradually expanded and changed to reach more students and become more inclusive and diverse, is a success as indicated by front-and-back evaluation. Finally, well over 30 undergraduate students and six graduate students have received research training on this grant, with several students presenting their research at conferences, contributing to manuscripts, and participating in research-related outreach events through the Burke Museum.

Last Modified: 11/20/2020
Modified by: Caroline Stromberg