The widespread misconception about the Japanese major biogeographic boundary, the Watase line (Tokara gap), revealed by bibliographic and beta diversity analyses

Abstract

The biota of the Japanese Archipelago is divided into the Palearctic and Oriental realms by the Watase line (Tokara gap), a major biogeographic boundary of Japan. This boundary is generally placed between Akusekijima and Kodakarajima Islands of the Tokara Archipelago, and has been the subject of many biogeographic debates. However, despite being widely accepted, the position of the boundary is doubtful because of a lack of clear evidence. Here, to verify the definition and existence of the biogeographic boundary, we performed a documentary search and beta diversity analysis of multiple taxa. Our documentary search suggested that the Watase line (Tokara gap) should be put between Yakushima/Tanegashima and Amamioshima Islands, but recent references to it clearly deviate from its original definition, and that the placement of the boundary line between Akusekijima and Kodakarajima Islands is based on limited and biased evidence. Our beta diversity analyses found no common biogeographic boundary dividing the Tokara Archipelago into two realms, and showed that the beta diversity pattern of this region is explained by the areas and geographic distances of the islands in agreement with the general principles of island biogeography. The widespread misunderstanding of biogeography in this region could have been perpetuated by preconception and the citation of references without verification. Our study proposes that revision of the biogeography in the Tokara Archipelago, a gap region between the Palearctic and Oriental realms, is necessary and demonstrates the negative influence of preconception in biogeographic debate.

Demographic Inferences and Loci Under Selection in a Recently Expanded Coral Population

“…Nakabayashi et al [31] found three genetically distinct lineages of A. hyacinthus using microsatellite markers and confirmed the presence of only one A. hyacinthus lineage within the temperate region. This divergence between mainland Japan and the Ryukyus has also been observed for a number of terrestrial (reviewed in [32]) and marine species [33]- [42] between the terrestrial biogeographical barrier called the Watase line (also referred to as the Tokara gap). This temperate-subtropical genetic separation has been attributed to allopatric speciation during glacial maximums [39], [41]- [43], the opening and closing of oceanographical barriers facilitated by shifts in the Kuroshio current during glacial maximums [34], [35], [40], [43], and divergent environmental selection pressures [36], [37], [44].…”

Widespread misperception about a major East Asian biogeographic boundary exposed through bibliographic survey and biogeographic meta‐analysis

“…Documents including articles and books referred to in any of the above-mentioned documents were further checked. A preprint related to the current study published in bioRχiv was not considered (Komaki & Igawa, 2017).…”

Revision of Japanese species of Nipponomyia Alexander, 1924 (Diptera, Pediciidae)

“…The island is characterized by a unique wet climate, which ranges from subtropical to high alpine climates, and hosts numerous endemic species ( Yahara et al 1987 ; Smith and Kamiya 2006 ; Shibasaki 2018 ). Yakushima is located in the southern boundary of Palearctic faunal realm, and the new biogeographic boundary between the Palearctic and Oriental realm was proposed between Yakushima/Taneshima and Amami Islands ( Komaki and Igawa 2017 ). The crane fly fauna of the island is poorly known, at the moment only six species are known as endemic to the island; however, the second author has an additional 8–10 undescribed species from Yakushima.…”