Biology subjects

Tojo, K.

Publications and source records attributed to Tojo, K..

10 recordsLinked to original sources

bioRxiv2026

Comparing the Influence of Habitat Configuration on Population Connectivity and Genetic Structure Using Congeneric Species Across Multiple Taxa

Abstract Habitat configuration influences population connectivity and, consequently, genetic structure. River networks provide heterogeneous, hierarchically arranged environments that shift drastically from upstream to downstream. We compared congeneric species across Ephemeroptera, Plecoptera, and Trichoptera, emphasizing longitudinal replacement (upstream to downstream) and the rarely studied wet rock (hygropetric) habitats. We surveyed six rivers on the Muroto Peninsula, Japan, qualitatively sampling aquatic insects at 63 sites. Cluster analysis based on the environmental data classified surveyed sites into four clusters. We analyzed a total of 10 species from four genera that exhibit longitudinal replacement patterns within genera. Genetic analyses based on the mitochondrial cytochrome c oxidase subunit I region revealed that upstream species showed higher genetic diversity than downstream species. In contrast, species adapted to hygropetric exhibited the lowest genetic differentiation among all habitat types. A novel contribution of this study is the inclusion of hygropetric species. The surprisingly low differentiation in hygropetric species suggests high connectivity, similar to lentic species. By comparing congeneric taxa across orders within environmentally similar rivers, we reduce phylogenetic and environmental confounds, strengthening inference that habitat configuration and dispersal traits jointly shape genetic structure. These findings provide a new perspective on riverine spatial ecology and underscore the importance of microhabitat-aware comparisons for evolutionary inference.

zoology↗

bioRxiv2026

Genetic structures of the Japanese stone loach Barbatula oreas (Cypriniformes: Nemacheilidae) in Sakhalin and Hokkaido: back dispersal from Hokkaido to Sakhalin

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.

Molecular Biology↗

bioRxiv2025

Changes over a 10-year Period in the Distribution Ranges and Genetic Hybridization of Three Pelophylax Pond Frogs in Central Japan

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.

ecology↗

bioRxiv2023

Cryptic connectivity between hyporheic and riparian zones via winged aquatic insects revealed by DNA barcoding

How subsurface hyporheic zone (HZ) of rivers is connected to riparian zones remains largely unknown. We collected benthic macroinvertebrates and adult aquatic insects for six years, including those at 30-cm depth in the HZ to identify insect taxa having a high level of habitat affinity for HZ (HZ taxa). Adults of HZ taxa were identified with the aid of CO1 gene barcoding, and the relative abundance of HZ taxa in the riparian zone was quantified. In addition to the previously known stonefly Alloperla ishikariana, three species of stonefly Leuctridae and one caddisfly species of Philopotamidae were identified as HZ taxa. At the annual scale, HZ taxa accounted for approximately 38% of the total aquatic insects in the family of stoneflies (Plecoptera), caddisflies (Trichoptera), and mayflies (Ephemeroptera) in abundance and 26% of biomass, with their seasonal peaks in early spring and mid-summer (60% in abundance and 47% in biomass). Few individuals of HZ taxa were found in benthic samples (<0.1%), and hyporheic samples quantified more but erroneously estimated relative abundances of adult HZ taxa, with Leuctridae and Philopotamidae being substantially underrepresented relative to their adult abundance. Cryptic biological connectivity between subsurface and riparian zones via winged HZ-taxa adults is substantial. DNA-based species identification combined with community surveys of adult HZ-taxa complementarily used with benthic data can substantially improve the effectiveness of biomonitoring programs and outcomes of habitat conservation based on more complete picture of ecosystem health.

ecology↗

bioRxiv2023

Definitive environmental DNA research on aquatic insects: Analysis optimization using the recently developed MtInsects-16S primers set

Long-term biodiversity monitoring is necessary for the conservation and management of water resources. Notably, aquatic insects have been used as an indicator of water quality because they provide important basic information about freshwater ecosystems and water resources. Although environmental DNA (eDNA) surveys can enable easy and effective biomonitoring of aquatic insects, previous studies have not successfully detected all insect species, and there has been frequent amplification of nontarget taxa (e.g., algae and diatoms). Therefore, we developed a universal primers set, MtInsects-16S, for eDNA analyses of insects in the mtDNA 16SrRNA region. Furthermore, a well-established database of aquatic insects, especially the MtInsects-16S DNA region of Ephemeroptera, Plecoptera, and Trichoptera in Kanagawa Prefecture, which was the target area in this study, was constructed. Therefore, in this study, we conducted eDNA analyses using a universal primers set and using a well-established database. We conducted and compared capture surveys at the same sites to examine the detection capability of eDNA for Insecta. As a result, eDNA analyses using MtInsects- 16S not only detected almost all of the captured species but also detected many more species without amplifying nontarget taxa. This study demonstrated the application of eDNA analyses with unprecedented accuracy and reliability. It was also shown that community structure by eDNA reflected a relatively narrow range at the water sampling point. Although the data accumulation for constructing locally specific databases is an urgent issue, using the MtInsects-16S region is expected to be a breakthrough in the metabarcoding of insects.

zoology↗

bioRxiv2022

Phylogeography of Geothelphusa freshwater crabs: unexpected dual dispersal routes via land and sea

AimDispersal is an important factor that determines the potential for colonization to pioneer sites. Most decapods employ seaward migration for reproduction with a planktonic larval phase. However, true freshwater crabs spend their entire life cycle in freshwater. Therefore, it is expected that genetic regionality can be easily detected. In this study, we focused on the genetic structures of true freshwater crabs, Geothelphusa crabs. Herein, we reveal the evolutionary history and dispersal patterns of freshwater crustaceans, for which there is limited knowledge to date. LocationJapanese Islands TaxonGeothelphusa dehaani (Decapoda, Potamidae) MethodsWe collected and genetically analyzed 283 specimens at 138 localities from freshwater habitats across the Japanese Islands. Phylogenetic analyses were conducted on 1,796 bp of the combined dataset (mtDNA COI, 16S, and nDNA ITS1, histone H3) and 569 bp of the mtDNA COI dataset. The demographic history of G. dehaani was simulated using Approximate Bayesian Computation analysis. A salt tolerance experiment was conducted to confirm the survival rate in seawater. ResultsThe resulting of phylogenetic relationships detected 10 clades that were highly likely to be monophyletic. These 10 clades genetically exhibited an explicit pattern of geographical differentiation. Also, we confirmed the salt tolerance ability of these Japanese freshwater crabs. Main conclusionsThe highlights of this study were the discovery of several cryptic species/lineages or undescribed species, and the completely different heterogeneous dual dispersal pathways detected within a single species; i.e., both land and ocean routes. As a result of phylogenetic analysis, it was concluded that Japanese crabs are basically genetically divided by straits. However, strong evidence for dispersion via ocean currents was also detected (i.e., a "sweepstake"), and it was also determined that G. dehaani could survive in seawater. This is the first observation of such a unique mode of expansion of a species distribution area.

zoology↗

bioRxiv2022

Long-read HiFi Sequencing Correctly Assembles Repetitive heavy fibroin Silk Genes in New Moth and Caddisfly Genomes

Insect silk is an incredibly versatile biomaterial. Lepidoptera and their sister lineage, Trichoptera, display some of the most diverse uses of silk with varying strength, adhesive qualities and elastic properties. It is well known that silk fibroin genes are long (> 20 kb) and have many repetitive motifs. These features make these genes challenging to sequence. Most research thus far has focused on conserved N- and C-terminal regions of fibroin genes because a full comparison of repetitive regions across taxa has not been possible. Using the PacBio Sequel II system and SMRT sequencing, we generated high fidelity (HiFi) long-read genomic and transcriptomic sequences for the Indianmeal moth (Plodia interpunctella) and genomic sequences for the caddisfly, Eubasilissa regina. Both genomes were highly contiguous (N50 = 9.7 Mbp/32.4 Mbp, L50 = 13/11) and complete (BUSCO Complete = 99.3%/95.2%), with complete and contiguous recovery of silk heavy fibroin gene sequences. This study demonstrates that HiFi long-read sequencing can significantly help our understanding of genes with highly contiguous, repetitive regions.

genomics↗

bioRxiv2021

Development of novel PCR primer sets for DNA metabarcoding of aquatic insects, and the discovery of some cryptic species

DNA barcoding is a powerful tool that provides rapid, accurate, and automatable species identification by using standardized genetic region(s). It can be a powerful tool in various fields of biology such as for revealing the existence of cryptic species and/or rare species and in environmental science such as when monitoring river biota. Biodiversity reduction in recent times has become one of the most serious environmental issues on a worldwide scale. DNA barcoding techniques require the development of sets of universal PCR primers for DNA metabarcoding. We tried to develop universal primer sets for the DNA barcoding of all insect groups. In this study, we succeeded in designing not only universal primer sets for DNA barcoding regions of almost all insects, which were designed to include a hypervariable site between highly conserved sites, but also primer sets for longer fragment sequences for registration in a database. We confirmed successful amplification for 14 orders, 43 families, and 68 species with DNA barcoding in the mtDNA 16S rRNA region, and for 13 orders, 42 families, and 66 species with DNA barcoding in the mtDNA 12S rRNA region. A key feature is that the DNA fragments of the DNA barcoding regions amplified by these primer sets are both short at about 200-bp, and longer fragment sequences will increase the level of data registration in the DNA database. Such resulting database enhancements will serve as a powerful tool for increasingly accurate assessment of biodiversity and genetic diversity.

ecology↗

bioRxiv2020

Development of microsatellite markers for a giant water bug, Appasus japonicus, distributed in East Asia

We developed microsatellite markers for Appasus japonicus (Hemiptera: Belostomatidae). This belostomatid bug is distributed in East Asia (Japanese Archipelago, Korean Peninsula, and Mainland China), and often listed as endangered species in the Red List or the Red Data Book at the national and local level in Japan. Here we describe twenty novel polymorphic microsatellite loci developed for A. japonicus, and marker suitability was evaluated on 56 individuals from four A. japonicus populations (Nagano, Hiroshima, and Yamaguchi prefecture, Japan, and Chungcheongnam-do, Korea). The number of alleles per locus ranged 1-12 (mean = 2.5), and average observed and expected heterozygosity, and fixation index per locus were 0.270, 0.323, and 0.153, respectively. The 20 markers described here will be useful for investigating the genetic structure of A. japonicus populations, which can contribute in population genetics studies of this species.

molecular biology↗

bioRxiv2020

Development of Microsatellite Markers for a Soricid Water Shrew Chimarrogale platycephalus, and the Success of Individual Identification Using It.

The soricid water shrew, Chimarrogale platycephalus, is a mammal species endemic to the Japanese Islands. They inhabit the islands of Honshu and Kyushu, and are considered to be extinct in Shikoku. Information on this water shrew from Honshu and Kyushu is also scarce, and C. platycephalus is registered on the Japanese Governments red list as an endangered species. Almost all study areas such as regarding their ethology, ecology, also their phylogenetics are lacking. The delay in these foundational studies is due to difficulties related to them being both nocturnal and aquatic. In order to study of C. platycephalus, it is essential to conduct field research in mountain streams at night under such circumstances. In response to such difficult circumstances, we established a genetic analysis method using the feces of C. platycephalus, and as a result the accumulation of data on their phylogenetic evolution and phylogeography has increased which has improved our understanding of this species. Furthermore in this study, development of microsatellite markers was carried out, and a total of 21 loci marker analyses were performed. In addition, in order to confirm the credibility of these 21 microsatellite markers, as being able to validly differentiate individuals, all markers were examined using the fecal and tissues specimens from verified separately reared individuals (12 individuals) with the known history of having been reared in an aquarium. As a result, it was revealed that if analyses of the 12 loci were possible, individual differentiation with 100% accuracy was possible. The development of microsatellite markers in this study, and the establishment of individual identification methods by means of this will be expected to greatly contribute to future ecological and ethological research, population genetics and biogeographical research of the water shrew, C. platycephalus.

evolutionary biology↗