Plants

Elucidating the origin of plants endemic to the Ogasawara Islands – two species of the genus Yarod have diverged from different ancestral species – | University of the Ryukyus

Overview
Associate Professor Koji Takayama, Associate Professor, Graduate School of Kyoto University, Dr. Akihiro Nishimura, Associate Professor Hidetoshi Kato, Graduate School of Tokyo Metropolitan University, Associate Professor Akiyo Naiki, Research Center for Tropical Biosphere Research, University of the Ryukyus The research team revealed that through molecular phylogenetic analysis, the animals grown in the Ogasawara Islands Two endemic species Yarod diverged independently from different ancestral species.
It is believed that 125 or about 45% of the 280 vascular plant species that grow naturally in the Ogasawara Islands are endemic. However, it is unclear where the ancestors of these endemic species came from and when they reached the Ogasawara Islands and evolved into endemic species. Associate Professor Takayama and colleagues focused on two endemic species of the Oleander family (Apocynaceae and Oleander) that grow in the Ogasawara Islands, and in order to elucidate their evolutionary origins, they encompassed all related species in the surrounding area. Conducted. It was found that Yalord was closely related to Shimasokei growing in the Ryukyu Islands, and Hosobaya Road was closely related to Mariana Yalord growing in the Mariana Islands. It was also shown that each closely related species diverged approximately 1-2 million years ago. This study shows that in the Ogasawara Islands, two endemic species of the same genus diverged from completely different ancestral species, showing how complex the evolutionary origins of island flora are.
The research results were published in the online edition of the international journal “Molecular Phylogenetics and Evolution” on March 28, 2022 (local time).


Photo: Yalord (left) endemic to the Ogasawara Islands and Shoreya Road (right) endemic to the Volcano Islands (Photos: Akihiro Nishimura, Koji Takayama)

1.background
It is also known as an “evolutionary experiment ground” because of the many endemic species that can only be seen on ocean islands around the world, and has fascinated many people since ancient times. The Ogasawara Islands are no exception, with 125 species, or about 45% of the 280 species of vascular plants that grow naturally, considered endemic. As the geographical origin of the endemic plants of the Ogasawara Islands, 3 routes are assumed, mainly Japanese native elements, Oceania elements and Southeast Asian elements. However, it is not clear where these ancestral species came from or when they reached the Ogasawara Islands and evolved into endemic species. In this study, as part of elucidating the origin of plants endemic to the Ogasawara Islands, we focused on two endemic species of the Oleander family, Yarod and Hosobaya Road.
Yalord grows widely in the forests of the Ogasawara Islands (including Satoshi, Father, and Hahajima Islands), while Hosobaya Road is limited to North Iwo Jima and South Iwo Jima (including North Iwo Jima, Iwo Jima, and South Iwo Jima) of the volcanic archipelago. It grows in its original place. It is speculated that the two species have different origins because of the shape of their leaves and fruits and the size of their flowers. However, the genus Yarod, which includes these species, is widely distributed from the Indian Ocean archipelago to tropical Asia to the Pacific islands, and comprehensive DNA comparisons with closely related species including the surrounding areas have not yet been performed. In addition, Tiny Valley Road is a plant, and since it only grows on North and South Iwo Jima in the volcanic archipelago, it is difficult to even collect samples for DNA analysis.

2.Research methods and results
Its geographic location is the main reason why it is difficult to elucidate the origin of species endemic to the Ogasawara Islands. Since the Ogasawara Islands are far away from mainland Japan, Oceania, Southeast Asia and other vast land areas, it is difficult to narrow down the range of origin and ancestral species only from geographical conditions. This narrowing is even more difficult if seemingly closely related species are widely distributed, such as the Yarod genus. To overcome this problem, comprehensive sampling of closely related species including surrounding areas is essential. Therefore, in this study, researchers from Kyoto University, University of the Ryukyus, Tokyo Metropolitan University, and University of Guam cooperated to conduct field surveys in various places. 2017 Southern Iwo Jima Natural Environment Survey (Tokyo Metropolitan University, NHK, Tokyo Metropolitan University (now Tokyo Metropolitan University) Joint Survey), 2019 North Iwo Jima Natural Environment Survey (Tokyo Metropolitan University Survey) I got Hosobaya Road. In addition, a comprehensive molecular phylogenetic analysis was achieved using nucleotide sequence data of closely related species registered in DNA databases.
It turned out that the two endemic species of Yarod that grow in the Ogasawara Islands came from different ancestral species. According to molecular phylogenetic analysis, Yallord growing on Ogasawara Islands in Ogasawara Islands is closely related to Shimasokei in Ryukyu Islands, while Hosobaya Road growing in Volcanic Islands is closely related to Mariana Road in Mariana Islands. It becomes clear (Fig. 1). It was also shown that each closely related species diverged approximately 1-2 million years ago. On oceanic islands such as the Ogasawara Islands, the phenomenon of adaptive radiation in which an ancestral species diverged into multiple species is well known. However, this result strongly supports that the two endemic species of the genus Yarod did not come from a single ancestral species, but that different ancestral species had reached the Ogasawara Islands and evolved independently. Comprehensive comparative analysis with closely related species including surrounding areas reveals some complex evolutionary origins of marine island-endemic species.


Fig. 1 The Yalord and Hosobaya Roads growing in the Ogasawara Islands were formed by different common ancestors.

3. 3. Spillover, future plans
This study shows that the two endemic Yarod species that grow on the Ogasawara Islands formed from completely different ancestral species. Through a comprehensive analysis including the surrounding area, it was found that the species group thought to have formed from a single ancestral species of the Ogasawara Islands actually originated from different ancestral species.
About 1 to 2 million years ago, two endemic species of the Ogasawara Islands, Yarod, parted ways with related species. The Ogasawara Islands where Yalord grows are thought to be tens of millions of years old, so this value can be interpreted as being consistent with geological history. On the other hand, the volcanic archipelago where Tiny Valley Road is currently located is estimated to be only tens to hundreds of thousands of years old. In other words, the divergence time of the small valley road was earlier than the time when the islands were formed. In addition to estimation errors, the most closely related strains may not have been analyzed or have become extinct, which is why the divergence of endemic species predates the date of island establishment. .. From now on, it will be necessary to conduct a large-scale survey of the Mariana Islands, centering on Mariana Road, a close relative of the tiny Vallelu, to verify which possibility is appropriate.
The Ogasawara Islands have a unique ecosystem that is unprecedented in the world and is registered as a World Natural Heritage. On the other hand, the protection of natural ecosystems is also a major issue for the Ogasawara Islands. By elucidating the history and evolutionary processes of the plant species that make up the forest, it is expected that an in-depth understanding of how the unique ecosystem of the Ogasawara Islands is formed will add to the enormous vitality of conservation.

4. About the research project
This research was carried out by the Japan Society for the Promotion of Science (JP26290073, JP17H04609, JP20H03310, JP20K21446), the Showa Shotoku Memorial Foundation, the Yamada Science Foundation, the University of the Ryukyus Research Project Promotion Fund (17SP01302, H29-H31), the Environmental Restoration and Protection Agency: This is by the Promotion Fund[Problem No. 4-2003](JPMEERF20204003) with a research grant. The 2017 Southern Iwo Jima Natural Environment Survey was conducted by the Tokyo Metropolitan Government, NHK and Tokyo Metropolitan University (now Tokyo Metropolitan University), and the 2019 2019 Northern Iwo Jima Natural Environment Survey was conducted by Tokyo Metropolitan University.

<研究人员的评论>
During my field trips to the Volcanic Islands and Guam, I realized that Hosobaya Road and Mariana Road are two. At this point, as previously pointed out, I am halfway convinced that the two species of the Yarod genus of Ogasawara have different origins. I am excited to demonstrate this through molecular phylogenetic analysis. I hope to continue to fully elucidate the origin of species endemic to the Ogasawara Islands through enhanced collaboration with researchers in the surrounding area. (Koji Takayama)

<文章标题和作者>
title:Multiple origins of two chloasma (Apocynaceae) endemic to the Bonin (Ogasawara) archipelago
Author:Hiroshi Noda, Akihiro Nishimura, Hidetoshi Kato, Akiyo Naiki, Wei Xiao, Mario Martinez, Mari Marutani, James McConnell, Koji Takayama

Publication:Molecular Phylogenetic and Evolutionary DOI: https://doi.org/10.1016/j.ympev.2022.107455

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