Using historical data to understand ecological and evolutionary processes: Biological invasions of non-native species present compelling motivation to understand how human-induced changes in the environment and species distributions influence ecological and evolutionary processes. Their documented geographic spread across time makes them ideal for study using historic collections, allowing better insight to evolutionary change over short time scales. Applying advanced genomic approaches to historic samples is key to understanding the processes that allow plants to rapidly establish and adapt to new environments. Theory predicts that dramatic ecological and evolutionary changes affect invasive species soon upon arrival in a new habitat. Yet current research relies on sampling contemporary populations, and therefore reveals little about the initial stages of invasion. Here, we study of the history of an invasive weed by exploiting an untapped historical resource to observe “snapshots” of the initial stages of invasion and the genetic changes that occur as a plant species spreads. It involves sampling genetic material from dried plant specimens collected throughout the course of an invasion, from herbarium collections across North America. Techniques for ancient DNA originally developed to study long extinct organisms such as mammoths are being used to study evolution over the course of the 100 year invasion of North America by crossflower (Chorispora tenella, Brassicaceae), a widespread and governmentally listed noxious invasive weed. See more at the project website, here.
Collaborators: Ruth Hufbauer, John McKay, Hernán Burbano, Rafal Gutaker
Invading hybrid Centaruea diffusa: Heterosis has also been hypothesized to contribute to invasion success. Previous work, including my comparison of transcriptome libraries from the native and invaded ranges (Lai et al., 2012), has shown that individuals of hybrid ancestry (with introgression from C. stoebe ssp. stoebe) are more common in the invaded than the native range, though hybridization occurs in the native range only. My work assesses the impact of this heterosis on phenotypic and genetic divergence in the invaded range.
Collaborators: Kate Ostevik, Loren Rieseberg
Genomic resources for Centaurea: New genomic tools are needed to elucidate the evolution of invasive, non-model organisms. This work aims to contribute to our genomic knowledge of the largest plant family, Asteraceae, and advance the study of invasion and evolution in Centaurea diffusa, a highly invasive weed species in North America. To date we have produced several such tools, including two transcriptome libraries for C. diffusa, and the complete plastid genome for C. diffusa, the first plastome from a genera containing approximately 250 species, and one of only 10 genera in this speciose family with a complete plastome assembly (available on GenBank as of June 2014). Future work will focus on a complete assembly of the rDNA, and survey assemblies of the mitochondrial and nuclear genomes for this species.
Collaborators: Chris Grassa, Loren Rieseberg
Human-assisted range expansion: A major constraint when studying invasive species to learn what enables a species to be invasive, is that you can only study the traits of the “winners” making it hard to distinguish correlation from causation. To learn about the effect of propagule pressure, pre-adaptation to anthropogenic contexts, and intra-specific introgression, we assess population structure and spread in an North American endemic wildflower, the Texas bluebonnet (Lupinus texensis). Endemic to central Texas and its state flower, the bluebonnet is a popular component of wildflower mixes sourced from commercial farms, and is spread along thousands of miles of highways in the southern US by the ton every year, and has thus expanded its range from New Mexico to Florida.
Collaborators: Daisie Huang, Quentin Cronk, Loren Rieseberg
Rapid evolution in the invaded range of Centaurea diffusa: Several hypotheses invoke trade-offs to explain a species invasive capabilities, including increased growth rate or reproductive capacity, relative to the native range which could lead to rapid spread and population growth. A shift in resource allocation between biotic or abiotic stress tolerance may allow for increased fitness in the invaded range. My work on Centaurea diffusa, the focus of my PhD, utilizes common garden experiments in both the greenhouse and the field, in the invaded and naturalized ranges of the species, to assess phenotypic differentiation between the ranges, to demonstrate differences in stress tolerance, and to test for the effect of abiotic environmental clines and maternal effects. Because gene expression may diverge more rapidly in response to selection, I also compare gene expression between the native and invaded ranges in reaction to severe drought.
Collaborators: Loren Rieseberg, Ruth Hufbauer, Hélène Fréville
Parallel evolution of weediness across the Asteraceae: Using a large data set of transcriptomes from across the Sunflower family, we look for evidence of positive selection, parallel evolution, and expansion load correlating with weediness both across and within species.
Collaborators: Kay Hodgins, Rob Colautti, Dan Bock, Sylvia Heredia, Emily Drummond, Min Hahn, Loren Rieseberg