Date of Award:

5-2016

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Paul G. Wolf

Committee

Paul G. Wolf

Committee

Zachariah Gompert

Committee

Michael D. Windham

Committee

Karen E. Mock

Committee

John Carman

Abstract

When we look at life on earth, we can see a lot of different life forms, but we still do not fully understand how these different life forms came to be and at which points in time these life forms began to be different enough from each other so we could call them by different names, or species. Some groups of species on earth, especially plants, seem to reproduce with each other, even though they are already very different from each other so that we call them different species. This process is called hybridization, and it can stir up the dynamics of these species, so that their basic building plans are changed very much. These changes can be either positive or negative for individual populations in such species, and in my research, I looked at a group of plant species in North America, which seem to reproduce very wildly among each other. For this, I traveled across the Western US and collected just a few leaves from many plants. With these leaves I managed to get a part of their basic building plan, which is also called DNA. This building plan carries the instructions to make the proteins that a cell needs, and these instructions are called genes. In different individuals of one species, the same gene can have very small changes. All of these changes in a group of individuals taken together are called genetic variation. This variation is good most of the time, but can also be pretty bad sometimes, because the proteins that are made do not work properly. When we look at the genetic variation between species, we can see how these species are related to each other. With the leaves I collected in the Western US, I did exactly that. I could show that a specific group of six different species, which someone called the Boechera puberula group, are related to each other more than to any other species out there. After that, I looked some more into one of these species, called Wasatch rockcress or Boechera lasiocarpa (which is its' fancy name for the scientists). When I looked at the DNA of this rockcress, I found that it actually has a lot of genetic variations, even though it only grows in a few different spots in the mountains of Northern Utah. I also saw that some of the populations I found had more variation than others. I then took four other Boechera species, that are very closely related to the ones I looked at earlier. One of the four species reproduces sexually, but the other three reproduce in a special asexual way, called apomixis. I grew these plants in the greenhouse, where some of them had just enough water, but others did not get enough water, so they were under drought-stress. I took their flowers, but this time, I did not look at the DNA, but I counted all of the proteins I could find in those flowers. I then compared the protein counts between the four species and found several interesting results. All of the four species did react in a different way to drought stress, and there were also lots of changes that were connected to how these species reproduce. The work that I briefly described here shows us different ways for how we can measure genetic variation between and within species. Taken together, my findings suggest that it is really important to not only look at different species when we want to measure genetic variation, but to also look at different populations, because these populations can be very different from each other. Further, when we try to make sense of the different reproductive modes in Boechera, there are a lot of little changes happening, that we have to take into account.

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