My research is focused on the evolutionary ecology of invasive and weedy plants, specifically how the genome structure evolves following introduction or in response to human management. I use a variety of approaches ranging from field and common garden experiments to molecular and chromosome analyses to understand how plant species evolve in novel environments. My work draws from the fields of genetics, genomics, evolution and ecology to link shifts in genome structure with shifts in fitness and traits. My studies of invasive species aim to provide both fundamental insights into  biology and practical information to land-managers regarding control of invasive species.

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EVOLUTIONARY ECOLOGY OF AN ALLOPOLYPLOID TUMBLEWEED

Allopolyploid speciation occurs when hybridization between divergent lineages is followed by whole genome duplication, which restores correct meiotic pairing and fertility to what might otherwise be a sterile hybrid. This results in a novel stable hybrid genome and reproductive isolation from the progenitor species. Recently available data from next-generation sequencing has demonstrated that polyploidy has played a major role in angiosperm evolution and illuminated the need for studies investigating evolution in recently formed polyploids. Moreover, both hybridization and whole genome duplication have been proposed to lead to the evolution of invasive species [2,3], making the role of allopolyploidy in plant evolution a particularly exciting topic. My previous research addressed the evolutionary ecology of a newly formed allopolyploid species. Salsola ryanii (Amaranthaceae) is an allopolyploid neospecies, formed through hybridization between two invasive species also within the genus Salsola (tumbleweeds). I showed that this species has undergone the most rapid known range expansion of an allopolyploid species [4] and has increased in fitness relative to its progenitor species. I also determined that this neospecies is the result of multiple origins reflecting repeated independent allopolyploidization events and abundant opportunities for this major evolutionary transition in the genome to contribute to invasion [5]. I will continue to use Salsola as a system to understand the role allopolyploidy in shaping invasive neospecies. The role of multiple independent origins of allopolyploid species in the success of allopolyploid neospecies is not well understood. I will build upon my previous work to understand range increase of different lineages through time, their trait differences, and competitive performance to determine how origins influence variation in fitness and invasiveness. Salsola is an exciting system to bring public interest to plant biology because it is a group that if familiar to many people through popular culture. This has generated strong press coverage of my past work (coverage in Newsweek, on several NPR stations including statewide in California and on several science blogs).

POPULATION GENOMICS AND GENOME EVOLUTION IN YELLOW STARTHISTLE

In my post-doctoral work with Dr. Katrina Dlugosch at University of Arizona I am investigating evolution following introduction in the rangeland invasive species yellow starthistle (Centaurea solstitialis). This species has evolved an increase in plant size, growth rate and flower/fruit production following introduction into California from Western Europe. I am using next-generation sequence data (RAD-seq) to detect areas of the genome that are under selection in introduced populations. Our ongoing work addresses open questions about the genetic architecture of adaptation in novel environments and the role of admixture between independent introductions in evolution of yellow starthistle in its invaded range. Preliminary data suggests that in yellow starthistle chromosomal structure evolution, specifically an inversion and genome expansion, are involved in genome evolution following introduction. Inversions can play an important role in rapid adaptation by preventing recombination within the area of the inversion therefor linking multiple genes together allowing a group of genes potentially involved in adaptation to spread as a group [1]. My current work is investigating the fitness consequences of genome structure evolution in the invaded range. I am launching a common environment comparison to directly connect the genome size and structure variants with fitness and traits of an individual. I am also using next-generation sequence data (RAD-seq) to detect areas of the genome that are under selection in introduced populations, and connect these patterns back to information about the location of chromosomal variants in the genome. This research will advance our understanding of the genomic basis of invasiveness and its potential consequences for management. Dr. Dlugosch and I look forward to continuing to collaborate on this work into the future.

ADVISING RESEARCH

Throughout my research, I enjoyed working closely with undergraduate students including members of underrepresented minorities in higher education. To provide the basis for independent research, I involve students with lab and field studies, experimental design and statistical analysis. I am particularly proud that a group of students whom I mentored published a peer-reviewed journal article with an undergraduate first author focused on barriers to gene flow between maize and teosinte [6]. These students are all currently utilizing skills they learned through this process in graduate programs. I have found that this research provides excellent opportunities for student involvement because it allows students to experience field, greenhouse, and laboratory work creating well-rounded scientists and allowing students to determine in what research direction their interests and passions lie.

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1 Hoffman AA, Sgro CM, and Weeks AR (2004) Trends in Ecology and Evolution 19(9):882-488.
2 Ellstrand NC and Schierenbeck KA (2000) Proceedings of the National Academy of Sciences 97(13):7043-7050.
3 Pandit MK, Pocock MJO, and Kunin WE (2011) Journal of Ecology 99(5):1108-1115.
4 Welles SR and Ellstrand NC (2015) American Journal of Botany 103(4):663-667.
5 Welles SR and NC Ellstrand (2016) Evolutionary Applications 9(7):781-787.
6 Chavez NB, Flores JJ, Martin J, Ellstrand NC, Guadagnuolo R, Heredia S, Welles SR (2012) Economic Botany 66:132-137.