Abstract
BackgroundIn contrast to the Western Palearctic and Nearctic biogeographic regions, the phylogeography of Eastern-Palearctic terrestrial vertebrates has received relatively little attention. In East Asia, tectonic events, along with Pleistocene climatic conditions, likely affected species distribution and diversity, especially through their impact on sea levels and the consequent opening and closing of land-bridges between Eurasia and the Japanese Archipelago. To better understand these effects, we sequenced mitochondrial and nuclear markers to determine phylogeographic patterns in East-Asian tree frogs, with a particular focus on the widespread H. japonica.ResultsWe document several cryptic lineages within the currently recognized H. japonica populations, including two main clades of Late Miocene divergence (~5 Mya). One occurs on the northeastern Japanese Archipelago (Honshu and Hokkaido) and the Russian Far-East islands (Kunashir and Sakhalin), and the second one inhabits the remaining range, comprising southwestern Japan, the Korean Peninsula, Transiberian China, Russia and Mongolia. Each clade further features strong allopatric Plio-Pleistocene subdivisions (~2-3 Mya), especially among continental and southwestern Japanese tree frog populations. Combined with paleo-climate-based distribution models, the molecular data allowed the identification of Pleistocene glacial refugia and continental routes of postglacial recolonization. Phylogenetic reconstructions further supported genetic homogeneity between the Korean H. suweonensis and Chinese H. immaculata, suggesting the former to be a relic population of the latter that arose when the Yellow Sea formed, at the end of the last glaciation.ConclusionsPatterns of divergence and diversity were likely triggered by Miocene tectonic activities and Quaternary climatic fluctuations (including glaciations), causing the formation and disappearance of land-bridges between the Japanese islands and the continent. Overall, this resulted in a ring-like diversification of H. japonica around the Sea of Japan. Our findings urge for important taxonomic revisions in East-Asian tree frogs. First, they support the synonymy of H. suweonensis (Kuramoto, 1980) and H. immaculata (Boettger, 1888). Second, the nominal H. japonica (Günther, 1859) represents at least two species: an eastern (new taxon A) on the northern Japanese and Russian Far East islands, and a southwestern species (n. t. B) on southern Japanese islands and possibly also forming continental populations. Third, these continental tree frogs may also represent an additional entity, previously described as H. stepheni Boulenger, 1888 (senior synonym of H. ussuriensis Nikolskii, 1918). A complete revision of this group requires further taxonomic and nomenclatural analyses, especially since it remains unclear to which taxon the species-epitheton japonica corresponds to.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0814-x) contains supplementary material, which is available to authorized users.
Highlights
In contrast to the Western Palearctic and Nearctic biogeographic regions, the phylogeography of Eastern-Palearctic terrestrial vertebrates has received relatively little attention
Our findings urge for important taxonomic revisions in East-Asian tree frogs. They support the synonymy of H. suweonensis (Kuramoto, 1980) and H. immaculata (Boettger, 1888)
The H. immaculata/H. suweonensis haplogroup is highly supported (99% bootstrap support, Fig. 2), it appears paraphyletic in respect to H. japonica
Summary
In contrast to the Western Palearctic and Nearctic biogeographic regions, the phylogeography of Eastern-Palearctic terrestrial vertebrates has received relatively little attention. In East Asia, tectonic events, along with Pleistocene climatic conditions, likely affected species distribution and diversity, especially through their impact on sea levels and the consequent opening and closing of land-bridges between Eurasia and the Japanese Archipelago. To better understand these effects, we sequenced mitochondrial and nuclear markers to determine phylogeographic patterns in East-Asian tree frogs, with a particular focus on the widespread H. japonica. The Eastern Palearctic, and notably the East-Asian region, called ‘Sino-Japanese’, has received less attention both in term of the number of investigated species and the geological timescales covered [1, 2] This area encompasses Eastern China, East Siberia and Far-Eastern Russia, Mongolia, the Korean Peninsula and the Japanese Archipelago. Komaki et al [17] recently compared mitochondrial and nuclear phylogenies in context to paleoclimatic modeling in East Asian water frogs (Pelophylax) from Far-Eastern Russia, China, the Japan, Korea and Taiwan and detected five historical mtDNA introgressions and range shifts, all considered to be shaped by glacial cycling
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