Genetic diversity and ecological success of the invasive riparian plant Mimulus guttatus

The study of biological invasions can help us to design effective strategies to prevent, and manage invasive species. Habitats associated with rivers and streams are particularly susceptible to biological invasion, both because of their natural levels of disturbance and because they are often subject of considerable man-made modification. Networks of river and streams facilitate the dispersal of invasive species which can potentiate their negative effects and make their control a challenging task. In fact, some of the most prominent invasive plant species in the UK occur in close association with water bodies (e.g. Himalayan balsam, giant hogweed, Japanese knotweed). Despite a long history of studying biological invasions in the UK, large gaps of knowledge exist in the structure of genetic variation of invasive riparian species. The distribution of genetic variation both within and between populations holds a trove of information regarding the history of introduction and spread of invasive species, the extent of genetic connectivity among them, and ultimately the potential of invasive species to keep adapting to novel environments and advance their spread under changing environmental conditions. Elucidating these biological patterns is the necessary first step towards designing lasting and successful strategies to deal with biological invasions.

Our study focuses on yellow monkey flowers (Mimulus guttatus), a widespread invasive plant that is mostly restricted to permanent and temporary bodies of running-water. It propagates both sexually via seeds and asexually through plant fragments carried by water. Monkey flowers were introduced to the UK from North America in the early 1800's, and are currently found throughout the British Isles. Monkey flowers are excellently suited for studying genetic and evolutionary processes during invasions. The ecology and evolution of monkey flowers has been extensively studied in its native range during the past 50 years, where it has become a model for studies of local adaptation, population structure, reproductive strategies, speciation, and genomics. No other UK invasive riparian plant has similar resources readily available, making M. guttatus the obvious choice for studying the ecological genetics of invasive species.

Here we will investigate the spatial genetic structure on an invasive riparian plant from broad geographic scales to small, within-population levels. In the first component of the work we will sample 40 populations of monkey flowers across the UK at different spatial scales from broad geographic regions to multiple populations within water catchments. The data generated in this component will allow us to determine the general genetic structure of monkey flowers in Britain, to test competing hypothesis of the pattern of colonization and spread of this species here, and to measure genetic connectivity across spatial scales. In the second component of the work we will sample at the fine spatial scale to estimate the rates of sexual and asexual reproduction, which is a fundamental determinant of the dynamics of invasive species. These data will allow us to calculate for the first time, the importance of asexual propagation to the structure of genetic variation and its relationship with ecological success in invasive monkey flowers. By combining genetic analyses with measurements of ecological success, we will infer historical patterns of invasion and connectivity between populations, and reveal whether the mode of reproduction correlates both with overall genetic diversity and ecological success.

Our project provides an exceptional opportunity to establish monkey flowers as a model for the study of biological invasions in the UK. This leading project will set the stage for future work on the ecology, evolution and management of invasive species in the UK and elsewhere.

CONSERVATION IMPACT
Our study will have a direct impact on conservation efforts in the UK, as Mimulus guttatus is a non-native group that has become well established in the British flora. National and local conservation groups will benefit from our study by gaining access to detailed accounts of population distribution and genetic connectivity of this invasive species in the UK. To facilitate access to the information generated here we will prepare a fact sheet for invasive M. guttatus in Britain and communicate it to relevant organizations including the Scottish Environment Protection Agency, the Environment Agency, Rivers and Fisheries Trust of Scotland, and PlantLife. Our published findings will also be submitted to online information repositories such as Conservation Evidence (http://www.conservationevidence.com) to maximize their impact on practical applications.

LAND MANAGEMENT IMPACT
Our study of the genetic connectivity in non-native species will be of special interest to plant managers dealing with the control of invasive plants. It will allow them to identify potential sources and sinks of invasive propagules, and to determine whether control efforts require separate strategies for spread through sexual or vegetative propagules. Importantly the genetic analysis proposed here will inform environmental managers on the spatial scale at which future control or eradication programs should be attempted. Our study will also indicate whether M. guttatus could serve as a biological indicator of the susceptibility of habitats to invasion by other similar species.

TRAINING IMPACTS
Postgraduate students will be recruited at different stages of the project to investigate related research questions as part of their degree training. Undergraduate students will be actively recruited to be involved in some of the experimental components of this proposal with the aim that these contributions will result in students' authorship of research papers.

PUBLIC ENGAGEMENT IMPACT
The data generated during this project will be of general interest. In the last two years, I have organized seminars targeted at the general public that have been publicized in local papers and attracted the general public for a lively discussion on evolution and society. I am also a member of the Botanical Society of the British Isles where I have contributed information regarding other invasive species for public dissemination via web pages (http://species. bsbi.org.uk/html/ solanum_rostratum.html). As part of the current project we will try to engage the public's interest in managing invasive species by giving public seminars and developing a simple webpage for quick reference and image-identification of the different groups of British Mimulus.