Koji Tojo

Understanding how dispersal and vicariance shape species distributions is a central goal in biogeography, yet the role of islands as sources of continental diversity remains poorly resolved. While multiple dispersal routes from the Eurasian continent to the Japanese Archipelago have been proposed, back dispersal from islands to the mainland is rarely documented, particularly in primary freshwater taxa constrained by marine barriers. Here, we investigated the population genetic structure and phylogeographic history of the Japanese stone loach Barbatula oreas , distributed in Hokkaido and Sakhalin, using mtDNA, nDNA, and genome-wide SNP data. We identified two differentiated Northern and Southern lineages within Hokkaido that diverged during the Pleistocene, indicating that geological events such as paleo-catchment reorganization, mountain uplift, and volcanic activity have shaped the present population structure. Ancestral area reconstruction based on mtDNA phylogeny identified Hokkaido as the origin of B. oreas and revealed dispersal from Hokkaido to Sakhalin, indicating back dispersal from islands toward the mainland. This pattern contrasts with the prevailing hypothesis of southward colonization from the continent via Sakhalin to Hokkaido. Additionally, low genetic differentiation between Hokkaido and Sakhalin suggested genetic exchange across the strait, consistent with paleo-catchment reconstruction indicating past catchment connectivity between the regions. These results highlight the combined roles of geological dynamics and sea-level fluctuations in shaping genetic structure, challenge the conventional continent-to-island dispersal paradigm. Moreover, our study demonstrates that island systems can act as biodiversity sources—not merely sinks—and provides a rare empirical example of back dispersal in primary freshwater species.

The geographic genetic structure and distribution within species are shaped by factors such as dynamic tectonic activity and topographic changes associated with climate change. We used the largely flightless, freshwater‐dependent beetle Zaitzeviaria ovata (Elmidae) as a model to investigate how ancient topography and dynamic geological history have influenced the distribution and genetic structure of riverine insects in the Japanese Archipelago. We sampled 169 localities across the Japanese Archipelago encompassing the distributional range of Z. ovata and conducted phylogenetic analyses using the mitochondrial DNA cytochrome c oxidase subunit I and 16S ribosomal RNA sequences, and the nuclear DNA arginine kinase, histone H3 and internal transcribed spacer 2 sequences to infer intraspecific genetic structure and estimate divergence times. While no clear geographic genetic structure was detected from the nuclear DNA, the mitochondrial DNA provided evidence of genetic relationships among populations corresponding to the influence of ancient topography and geological history. Five major genetic groups were identified from mitochondrial DNA, with diversification estimated to have occurred during the Pleistocene. In addition, subclades were detected within the clades centred in Eastern Japan and Kyushu Island. The genetic structure between and within clades is associated with the complex geological history of the Japanese Archipelago, including the presence of two ancient river systems that existed in Western Japan during glacial periods and large‐scale volcanic activity in Kyushu. The inferred genetic structure suggests recent secondary contact between populations on islands previously considered geologically isolated, highlighting the need to re‐evaluate conventional geological interpretations or the species' capacity for over‐seas dispersal. This study demonstrates that riffle beetles can provide valuable insights in phylogeographic research, and future studies using this group could further clarify the factors driving diversification in riverine species.

A new species of Leptocerus, L. bannamradensis sp. nov., is described and illustrated based on the male genitalia and molecular data. The male genitalia of L. bannamradensis sp. nov. are similar to those of L. glaukos Malicky & Chantaramongkol 2002 known from Sai Yok Waterfall, Kanchanaburi Province but differ distinctly in the inferior appendages: The basodorsal process of each inferior appendage is long and curved ventrad in L. bannamradensis sp. nov. while it is straight in L. glaukos. Additionally, fragments of mitochondrial genes, cytochrome c oxidase subunit I (COI) and 16S ribosomal RNA (16S rRNA), of the new species and Leptocerus dirghachuka, L. lampunensis were analysed.

The final-instar larva of Chimarra argax from southern Thailand is described and illustrated. The larva has a yellowish sclerotized head, pronotum, legs, and anal claws; the mesonotum, metanotum, and abdominal segments are membraneous. The anterior margin of the frontoclypeus in C. argax is slightly asymmetrical, featuring a central U-shaped incision flanked by two lump-like structures of unequal size, the left being slightly wider than the right. In addition, we analyzed the cytochrome c oxidase subunit I (COI) gene of the larva and confirmed adult material of C. argax, and compared the nucleotide sequences with those of closely related species. The resulting the COI Maximum Likelihood diagram supports the association of larval and adult C. argax as well as the assumption that C. argax is genetically distinct from C. shanorum, C. gether, and C. ariadne. Furthermore, C. argax and C. shanorum were assessed as being sister species forming a monophyletic clade.

By assessing the genetic structure and gene flow at the local population level, it is possible to visualize connectivity and barriers to migration and dispersal. We focused on the cold-adapted caddisfly Asynarchus sachalinensis Martynov, 1914 (Trichoptera: Limnephilidae) and conducted phylogenetic analyses based on information from single nucleotide polymorphisms. In addition to the two genetic lineages (groups A and B) detected by mitochondrial DNA analyses in a previous study, we discovered that A. sachalinensis is composed of three genetic groups, including group C, which originated from a hybridization of these previous known lineages. The origin of group C was estimated to be ∼.12 Ma and was evaluated to have a high level of gene flow within the group. We also evaluated gene flow within the same mountain massif, where genetic groups B and C live. The results clearly revealed restricted gene flow between the alpine and sub-alpine zones. These results indicate that previously differentiated populations of A. sachalinensis would have undergone a range shift owing to past climatic changes. However, some populations might have survived in refugia and still exist as populations isolated from others owing to topographic discontinuities and climatic differentiation. Moreover, we suggest that differences in their life cycles maintained lineage differentiation and promoted speciation.

In this study, we focused on interspecial interactions in Central Japan where three closely related pond frog species, Pelophylax nigromaculatus , Pelophylax porosus porosus , and Pelophylax porosus brevipodus (two species and two subspecies) are distributed and are in contact and/or overlap. The presence or absence of hybridization between these species was evaluated by comparing the sequences of the mitochondrial DNA Cyt‐b (586‐bp) and the nuclear gene Tyrosinase (747‐bp) regions of each specimen collected. By comparing interspecific hybridization in the same area in both 2010 (119 specimens) and 2020 (152 specimens), we clarified population distributions and corresponding genetic dynamics over a 10‐year period; there was no major change in the degree of interspecific hybridization between P. nigromaculatus and P. p. brevipodus in the Ina Basin, but it was revealed that the proportion of “pure”‐bred Pelophylax p. brevipodus remained low. On the other hand, in the Matsumoto Basin, interspecific hybridization between P. nigromaculatus and P. p. porosus was evaluated to have progressed slightly. The proportion of “pure”‐bred Pelophylax p. porosus declined to less than half, while the proportion of hybrid individuals showed a tendency to increase. Moreover, the dispersal of P. nigromaculatus was confirmed in areas along the Sai‐gawa River, where only the pure‐bred P. p. porosus was previously known to inhabit. Since the three frogs targeted in this study are all “Red List” species that are endangered, continuous monitoring of population structures and genetic dynamics is required.

Climate warming has profound effects on animal behavior, ecology, as well as on human activities. As the number of extreme weather events increases with climate warming, organisms are facing unprecedented environmental challenges. In temperate regions, winter food scarcity poses a critical survival challenge for many animals. This study investigated the unique foraging behavior of the Kamikochi population of Japanese macaque, Macaca fuscata, which forage for aquatic insects during severe winters with scarce food availability. In February 2024, a thermal event with rising temperatures and rain triggered snowmelt and river flooding, which made it difficult for the macaques to access aquatic food. Comparisons of foraging behavior during periods with and without the thermal event showed that Kamikochi macaques reduced their foraging on aquatic insects inhabiting streams during the thermal event. These findings highlight the ecological impacts of heating events expected to become more frequent due to climate change. Japanese macaques in Kamikochi provide valuable insights into how wildlife behavior may change in response to these events.

The evolutionary history of Chimarrogale platycephalus, an endangered water shrew endemic to Japan, was investigated. The method of genetic analysis based on faecal specimens established in our previous study was adopted. The present study promoted a deeper discussion of additional specific phylogenetic evolutionary scenarios, introduction of ecological niche modelling and divergence period estimation. Regarding the history of the phylogenetic evolution of the water shrew, the following scenarios were clarified. First, during the Pleistocene, an ancestral group of C. platycephalus migrated from the Asian Continent to Kyushu, and then to Honshu, expanding its distribution area in a southwest to northeast direction. During a period spanning the Calabrian to the Chibanian era, its distribution repeatedly contracted and expanded due to climate change. Its areas of distribution were reduced during glacial periods and expanded during interglacial periods. After differentiation into four genetic lineages from different refugia, two of these lineages are now in a state of secondary contact in Honshu. The distribution areas of these two lineages overlap over a wide area. This study investigated the genetic structures and evolutionary history of higher order predators in the ecosystems of Japanese streams and provides important results for conservation genetics.

In this study, we focused on interspecial interactions in Central Japan where three closely related pond frog species, Pelophylax nigromaculatus , Pelophylax porosus porosus and Pelophylax porosus brevipodus (two species and two subspecies) are distributed and are in contact and/or overlap. The presence or absence of hybridization between these species was evaluated by comparing the sequences of the mitochondrial DNA Cyt-b (586-bp) and the nuclear gene Tyrosinase (747-bp) regions of each specimen collected. By comparing interspecific hybridization in the same area in both 2010 (119 specimens) and 2020 (152 specimens), we clarified population distributions and corresponding genetic dynamics over a 10-year period; there was no major change in the degree of interspecific hybridization between P. nigromaculatus and P. p. brevipodus in the Ina Basin, but it was revealed that the proportion of “pure”-bred Pelophylax p. brevipodus remained low. On the other hand, in the Matsumoto Basin, interspecific hybridization between P. nigromaculatus and P. p. porosus was evaluated to have progressed slightly. The proportion of “pure”-bred Pelophylax p. porosus declined to less than half, while the proportion of hybrid individuals showed a tendency to increase. Moreover, the dispersal of P. nigromaculatus was confirmed in areas along the Sai River, where only the pure-bred P. p. porosus was previously known to inhabit. Since the three frogs targeted in this study are all “Red List” species that are endangered, continuous monitoring of population structures and genetic dynamics is required.