Demographic History and Genetic Diversity of Rātā Moehau (Metrosideros bartlettii; Myrtaceae), a Critically Endangered Aotearoa New Zealand Endemic Tree

Trees are a critical part of terrestrial ecosystems, but a large proportion of the world's trees are at risk of extinction. Targeted conservation efforts will be crucial to maintaining these species in the face of climate change and other anthropogenic impacts. When populations become small, they are increasingly susceptible to the negative genetic impacts of small population size and inbreeding. Understanding demographic history and genetic diversity of threatened species can facilitate the development of effective conservation management plans. Rātā Moehau (Metrosideros bartlettii, Myrtaceae) is an example of a Critically Endangered Aotearoa New Zealand endemic tree treasured by Māori, the Indigenous Peoples of Aotearoa. With just 14 wild individuals remaining, we implemented a study to assess the genetic diversity and infer demographic history to inform conservation management. We have sequenced and assembled the first genome for rātā Moehau, and generated resequencing data for wild and cultivated individuals. Using demographic reconstruction, we inferred a long-term decline in population size over the past 1 million years. Further, cultivated individuals were found to have reduced diversity compared with wild individuals. Quantifying these genetic characteristics provides useful information for restoration decision-making by conservation practitioners, led by local iwi (tribes).