Hybridization has the power to create and destroy genetic diversity, and consequently can facilitate or hinder a species' ability to withstand changing environmental conditions. Because of this duality, the evolutionary role of hybridization in nature is poorly understood. This research will utilize recent developments in high-throughput sequencing to examine the evolutionary consequences of hybridization in a widespread radiation of garter snakes. This model system demonstrates the signature of hybridization in the past, as well as ongoing, replicated hybridization in the present. Theoretical predictions regarding the consequences of hybridization on evolution will be tested by connecting genomic data with variation in adaptive traits. Such variation is the raw material for evolution and consequently, the most useful measure of a population's ability to adapt to changing conditions.
Understanding the effect of hybridization on evolutionary potential is of critical importance to management of invasive species (which are frequently of hybrid origin) and the conservation of threatened species (which are often threatened by hybridization). This study will help connect a predictive theoretical framework with a natural study system, an essential step towards making theory operational for applied management decisions. Furthermore, this research will be used to address the failure of standard teaching methods to connect Mendelian genetics with the evolution of complex traits. By introducing students to this important but often neglected step, this project will help address widespread misunderstandings about the evolutionary process.
Evolutionary biologists have developed sophisticated theory, validated by field studies, for understanding how the forces of natural selection, migration and genetic drift cause the evolution within populations. Furthermore, data collected from across the tree of life combined with molecular DNA sequences has allowed us to detect large-scale, macroevolutionary patterns of evolutionary change. To what extent can we explain the patterns observed at the macroevolutionary scale (change over millions of years) with our population-level theory (change over a few generations)? Understanding the answer to this question is essential toward understanding how the mechanisms of evolution we understand at the population-level scale up to allow long-term species survival and persistence in a rapidly-changing world. This project examined these questions by taking a multi-level approach. First, we demonstrated that the rate of evolution over short timescales is actually much faster than what it would need to be to explain the range of biodiversity we see today using large collections of evolutionary data collected over the last 150 years. Even so, we observe a remarkably continuous and unified pattern of evolutionary trait change over timescales from a few years, to several hundreds of millions of years, indicating that data collected from numerous different sources and timescales is giving a unified picture of evolutionary change. Given this continuity, we asked what evolutionary mechanisms could slow evolutionary change as we scale up from our population-level understanding, to the macroevolutionary patterns we observe across existing biodiversity. To do this we examined the a highly-variable and widespread group of snakes that has split into numerous species across North America. Using genetic markers, we demonstrated that large amounts of migration and hybridization occurred both within distinct races of a single species, as well as a signature of hybridization with several other species in the radiation. Furthermore, we demonstrate that there is a signature of repeated cycles of range expansion and contraction leading to repeated cycles of evolutionary change among isolated populations and hybridization where previously isolated populations meet again upon range expansion. We suggest that this pattern of evolutionary change results in rapid evolution over short-timescales, but that these episodes of species fusion and the extinction of small populations slows evolution in the long-term. Finally, we develop a method for integrating population-level theory and field data into studies of the pattern of evolution across the tree of life. This methodology will provide a framework for quantitatively studying these two different scales, and highlighting the deficiencies of our existing theory. The results of this research were used in two workshops targeting underserved high schools which were brought to Oregon State University, as well as numerous school and classroom visits. We developed and presented a teaching module that explains how Mendelian genetics can scale up to explain the large-scale evolutionary changes we observe between species to high school teachers and to students. This project highlights the need for increased focus on connecting the macroevolutionary patterns and microevolutionary processes, and demonstrates that there is fertile ground for unifying data and theory across this perceived divide.
