Endemic Plants of St. Helena: Potential for Rescue, Inherent Variation within Species, and the Future of Babies’ Toes and the Lowland Desert Habitat https://sthelenaisland.info/flora/scrubwood/ Melissa Starkey August 2020 Thesis submitted in partial fulfillment of the MSc in the Biodiversity and Taxonomy of Plants. Acknowledgements Special thanks to my supervisor, Dr. Alan Gray, for his guidance, support, expertise, and good discussions. His enthusiasm about St. Helena was contagious from the start. Thanks also to my co-supervisor, Dr. Greg Kenicer for helpful comments and feedback on my project. I am indebted to Gerrie, Scott, and Kay, for their unwavering support both at home and from afar. i Abstract St. Helena is a remote volcanic island in the South Atlantic Ocean with a diverse topology and a rich endemic flora. Due to anthropogenic factors, many plant species have been reduced to small, severely fragmented populations, resulting in genetic erosion and a more limited ability to adapt to environmental pressures. This thesis addresses conservation of St. Helena’s endemic flora relating to themes of genetic variation and climate change. Chapter one introduces the island and its flora. Chapter two reviews the literature on genetic rescue in plants and shows that it can be beneficial for small, fragmented populations, though additional research is needed. Chapter three conceptually applies the genetic rescue approach to St. Helena’s critically endangered endemic plants, many of which are promising candidates for the strategy and are predicted to be heading rapidly towards extinction. Chapter four assesses historical levels of variation through morphometric analysis using herbarium specimens of three endemic St. Helena genera: Carex L., Phylica L., and Wahlenbergia Schrad. ex Roth; proposes areas for further research and conservation, and addresses taxonomic issues for Carex. Chapter five discusses potential impacts from climate change and increased tourism in St. Helena’s lowland desert habitat and proposes conservation actions and future research directions. Chapter six provides a brief conclusion to the thesis, which will contribute valuable insights for informing conservation decisions on St. Helena. ii Table of Contents Acknowledgements ......................................................................................................................................................... i Abstract ................................................................................................................................................................................. ii Chapter 1: Introduction and Aims .......................................................................................................................... 1 The Island of Saint Helena ......................................................................................................................................... 1 The Flora of Saint Helena ........................................................................................................................................... 2 Extinction of and Threats to St. Helena’s Flora ................................................................................................. 4 Conservation Efforts on St. Helena ......................................................................................................................... 7 Thesis Aims ...................................................................................................................................................................... 8 Chapter 2: Genetic Rescue as a Conservation Strategy ............................................................................. 9 Introduction ..................................................................................................................................................................... 9 Genetic Rescue: One Potential Solution ............................................................................................................ 10 What Can Go Wrong? Potential Issues and Shortcomings of Genetic Rescue ........................ 11 The Role of Genomics .................................................................................................................................... 12 Genetic Rescue Trials in Conservation ................................................................................................... 13 Review of the Evidence for Genetic Rescue with an Emphasis on Plant Studies ............................. 14 Genetic Rescue Reviews ............................................................................................................................... 14 Recent Studies in Plants ............................................................................................................................... 17 The Ideal Study ................................................................................................................................................. 18 Source Plant Material for Genetic Rescue ............................................................................................. 22 Published Recommendations and Assessment Tools for Genetic Rescue .......................................... 22 Barriers to Implementing Genetic Rescue ....................................................................................................... 26 Remaining Questions and Research Gaps ........................................................................................................ 26 Chapter 3: Prospects for Genetic Rescue of St. Helena’s Endemic Flora ....................................... 28 Status of St. Helena’s Endemic Flora .................................................................................................................. 28 Assessment of St. Helena Plant Species as Candidates for Genetic Rescue ........................................ 29 Outbreeding Depression Risk Assessment ........................................................................................... 33 Genetic Rescue Assessment ........................................................................................................................ 34 Additional Considerations ........................................................................................................................... 34 Potential Sources of Plants for Genetic Rescue Attempts ............................................................... 35 Additional Research Needed ...................................................................................................................... 36 Conclusion ..................................................................................................................................................................... 37 Chapter 4: Morphometrics to Assess Genetic Variation in Endemic Plant Species from St. Helena ................................................................................................................................................................................. 39 Introduction .................................................................................................................................................................. 39 Carex dianae....................................................................................................................................................... 40 iii Phylica polifolia ................................................................................................................................................ 41 Wahlenbergia Species .................................................................................................................................... 42 Aims ................................................................................................................................................................................. 44 Materials and Methods ............................................................................................................................................. 44 Specimens ........................................................................................................................................................... 44 Selected Characters and Specimen Measurements ........................................................................... 44 Statistical Analyses ......................................................................................................................................... 45 Results ............................................................................................................................................................................. 46 Carex dianae....................................................................................................................................................... 46 Phylica polifolia ................................................................................................................................................ 47 Wahlenbergia Species .................................................................................................................................... 50 Discussion ...................................................................................................................................................................... 54 Carex dianae......................................................................................................................................................