DATE2025.12.19 #Press Releases
Hidden Species Diversity Revealed by Mitochondrial Genome Analysis
-Terrestrial Ribbon Worms in the Ogasawara Islands Represent a Distinct Lineage from Widely Distributed Species-
Summary
A research team led by Natsumi Hookabe, Research Institute for Global Change (RIGC), Japan Agency for Marine-Earth Science and Technology (JAMSTEC); Associate Professor Shimpei Hiruta of The Mt. Fuji Institute for Nature and Biology, Showa Medical University; Naoto Sawada, Project Researcher and Associate Professor Rei Ueshima at the Graduate School of Science, The University of Tokyo; and Professor Hiroshi Kajihara of the Faculty of Science, Hokkaido University, conducted comparative morphological analyses and mitochondrial genome–based molecular phylogenetic analyses to clarify the taxonomic identity of terrestrial ribbon worms distributed in Japan.
Terrestrial ribbon worms from the Ogasawara Islands had long been regarded as the same species as Geonemertes pelaensis Semper, 1863, a species originally described from Palau and thought to be widely distributed across tropical and subtropical islands worldwide. However, recent studies revealed that individuals from the Ogasawara Islands exhibit different prey preferences from those in other regions, raising concerns about their potential ecological impact on the terrestrial ecosystems of the islands.
Ribbon worms (phylum Nemertea) are notoriously difficult to identify based solely on external morphology. Despite this, species identification of terrestrial ribbon worms in the Ogasawara Islands had historically relied only on morphological characteristics, and no DNA-based data had been available. In this study, the researchers analyzed terrestrial ribbon worms collected from the Ogasawara Islands and Yonaguni Island (Okinawa Prefecture) using mitochondrial genome–based molecular phylogenetic analyses, along with detailed comparisons of external and internal morphological features.
The results revealed that two distinct groups, corresponding to species-level differences, occur within Japan: an Ogasawara lineage and a widely distributed lineage. The Ogasawara lineage differed markedly from the widely distributed lineage—found across islands in the Pacific and Atlantic Oceans, including Yonaguni Island—in mitochondrial genome size, gene arrangement, and morphological characteristics.
Furthermore, re-examination of museum specimens collected on Chichijima Island in the 1980s and currently preserved at the Naturalis Biodiversity Center in the Netherlands showed that these historical specimens share nearly identical characteristics with present-day individuals from the Ogasawara Islands. This finding strongly suggests that the same lineage has been established in the Ogasawara Islands for at least several decades.
This study not only demonstrates the existence of previously overlooked hidden species diversity among small invertebrates, but also highlights the importance of long-term monitoring that integrates continuous field surveys with the effective use of museum collections for the conservation of island ecosystems.
The results of this study were published online in BMC Ecology and Evolution on December 19 (Japan Standard Time).
Figure：Geographic Distribution and Genetic Differentiation of the Genus Geonemertes
A molecular phylogenetic analysis based on partial sequences (573 bp) of the mitochondrial COX1 gene revealed a clear separation between the Ogasawara lineage (orange) and the widely distributed lineage (blue), which is found in regions including Bermuda, Cuba, Martinique, New Caledonia, and the Ryukyu Islands. The results demonstrate that both lineages occur within Japan.
(Adapted and translated into Japanese from the original article under the CC BY-NC-ND 4.0 license.)
Links
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Showa Medical University, Hokkaido University
Journals
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Journal name BMC Ecology and EvolutionTitle of paper