Genetic Study of Common Purslane on Nishinoshima Island

Nishinoshima Island is part of the Ogasawara Islands, located about 1,000 kilometers south of Tokyo. The island is renowned for its continuous volcanic activity, with a series of major eruptions in 2013 nearly destroying all vegetation. While this poses a disaster for the plants, the periodic ‘resetting’ and the island’s remote features provide scientists with a rare opportunity to study the origin and evolution of ecosystems in isolated environments.

Genetic Study of Common Purslane

A team led by Professor Koji Takaya from Tokyo Metropolitan University conducted a unique study on Nishinoshima Island. The team analyzed samples of the common purslane plant, or Portulaca oleracea, collected from the island in 2019 before eruptions wiped out the plants there. Although this plant species is widespread in temperate and tropical climates worldwide, the local population on Nishinoshima is now extinct.

The genetic analysis included rare samples from 254 individuals across 51 different communities in Japan and Guam. Through detailed comparison, the team began to uncover the origins of the Nishinoshima population and its place in the ‘family tree’ or genetic tree of this plant species.

Genetic Origins and the Founder Effect

By analyzing chloroplast DNA and conducting a comprehensive survey of nuclear DNA, the team was able to classify families based on genetic similarities. They found that the population on Nishinoshima was closely related to those on the nearby volcanic island of Chichijima. However, individuals from Nishinoshima exhibited distinct genetic traits.

The study also revealed that these plants originated from a very small number of individuals, leading to a strong deviation in subsequent genetic diversity, known as the founder effect. The flat and small seeds of purslane facilitate their spread by wind, birds, and ocean currents, but the analysis showed that the chances of the plant surviving on the island were extremely limited.

The Role of Environmental Events in Genetic Change

The analysis also uncovered genetic drift, where isolated events such as typhoons and volcanic eruptions play a role in altering genes instead of natural selection. The study provided an initial glimpse into the genetic analysis of the extinct population, offering insights into how populations settle through seed dispersal and how they survive and adapt to harsh environmental factors.

Conclusion

This study highlights the importance of the unique environment of volcanic islands in providing insights into the early stages of genetic evolution in isolated environments. It also sheds light on how plant populations are re-established following natural disasters. This work was supported by several research grants from Japanese research societies, indicating ongoing collaboration to support environmental and genetic evolution research.