A research group from Toyama University, Hokkaido University, and the Forestry and Forest Products Research Institute conducted an investigation into the Amami rabbit, long-haired rat, and spiny mouse species that are endemic to the Central Ryukyus, and revealed that the order and timing in which populations on each island separated varies depending on the species.
The high endemism of the biota in the Central Ryukyus (the central part of the Ryukyu Islands) is related to the long geographical history of the Ryukyu Islands, which spans several million years since they separated from the continent. However, there were many unknowns regarding the timing of habitation of Amami rabbits, long-haired rats, and spiny mice, which are terrestrial mammals, on the islands of the Central Ryukyus, and the genetic relationships between the island populations. In this study, the research group used genome-wide genetic analysis to investigate the relationships between populations living in the Central Ryukyus.
As a result, it was found that the populations on each island were genetically independent lineages for each species, but the order and timing of their divergence differed. For spiny rats, the Okinawa Island population was the most genetically distant, diverging from the populations on the other two islands more than 2 million years ago. The Amami Oshima and Tokunoshima populations were also estimated to have diverged at least 500 million years ago.
Meanwhile, Amami rabbits (Amami-Oshima and Tokunoshima) and long-haired rats (Amami-Oshima, Tokunoshima, and Okinawa Island) are estimated to have separated from each other during the Middle Pleistocene (approximately 12 to 78 years ago). The long-haired rats on Tokunoshima are distinctive, and were found to have been formed by the past merging of lineages from Amami-Oshima and Okinawa Island. Furthermore, for each species, the population on Amami-Oshima maintained a higher level of genetic diversity than the other islands.
The findings obtained in this study are important for understanding the evolution and population history of these endangered species, and for considering future conservation measures.
