Graduate Work

Beilstein adapted
The origins of the mustard and Pierid families coincide. After Beilstein et al 2010.

My graduate work focuses on understanding evolutionary interactions between plants and their herbivores. Specifically, I am interested in understanding how these interactions impact genetic diversity, plant defense strategies, and speciation. I plan to explore these questions using the Brassicaceae (mustards) and Pieridae (butterfly species) families, targeting the genes that produce defense chemicals in Brassicaceae and the detoxification gene that responds to these chemicals in Pierids. I am currently exploring several major questions for my thesis:

  • Is there evidence of positive selection in defense-related genes (especially in the glucosinolate biosynthetic pathway)?
  • Do abnormal selection patterns correlate with shifts in diversification rate?
  • Are there similar selective patterns in herbivore genes that respond to key plant defense traits?
  • Are there repeated clusters, or syndromes, of defensive traits?

I am also working on several side projects with collaborators and supporting independent student projects in my areas of interest. These include:

  • Transgenerational plasticity, epigenetic modification, and chemical defense
  • Interactions of pollinator shifts and diversification; ecological correlates of specific pollinators
  • Definitions and measurement of fitness when trying to understand local adaptation

More to come soon!

Undergraduate Work

Mining in the Santa Cruz sandhills

My undergraduate work focused on population genetics of rare and endangered soil specialist plants. This work was performed under Justen Whittall at Santa Clara University . I worked on two different species, Camissonia benitensis (San Benito Evening Primrose) and Erysimum teretifolium (Santa Cruz Wallflower). Both of these species are threatened by human destruction of their native habitats and are federally listed as endangered. The goal of these projects was to determine if populations of these plants were genetically structured to inform future reintroductions.

Erysimum teretifolium in the field

E. teretifolium inhabits the Santa Cruz sandhills, a unique inland dune formation resulting from an ancient sea that once covered the area. These sandhills form island-like habitats, which are separated by redwood forests that many of the native sandhill species do not live in or travel through. I hypothesized that E. teretifolium would have strongly differentiated populations as a result of this fact. However, E. teretifolium also has a partial SRK self-incompatibility system, which means individuals either are unable to mate with themselves and other closely related individuals, or these crosses will produce very few seeds. Because of this, E. teretifolium needs to maintain high genetic diversity within each population or have high levels of gene flow between populations. Potentially, this system could prevent the high level of population differentiation we would expect to see under an island model. I found that genetic diversity was highest within populations, meaning overall population structure was weak. Low population structure most likely means that E. teretifolium‘s mating system is more important than its habitat in determining its distribution of genetic diversity. Conservation groups looking to restore this species to sites where it was extirpated can use this data to justify mixing seeds from different populations. This work was the subject of my senior thesis.

The Camissonia work has been published and can be viewed here.

(c) 2015 Julie Herman

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