Biology subjects

Myosho, T.

Publications and source records attributed to Myosho, T..

4 recordsLinked to original sources

bioRxiv2026

Can carcasses cause environmental nucleic acid pollution? Implications for interpreting environmental RNA/DNA survey results

Environmental nucleic acid (eRNA and eDNA) metabarcoding is a promising tool for biodiversity assessment as it supports low-cost, noninvasive biological surveys. A critical challenge for eRNA/eDNA analyses is accounting for nucleic acid contamination that can compromise the accuracy of biomonitoring results. The primary aim of the current study was to examine carcasses as potential sources of eRNA/eDNA contamination, a contribution that remains poorly understood. Using Japanese medaka (Oryzias latipes), we quantified the detectability and persistence of carcass-derived eRNA/eDNA in water through two complementary experiments: (i) a shedding study comparing eRNA/eDNA release from live and dead individuals and (ii) a decay experiment measuring temperature-dependent degradation from 4 to 34 {degrees}C. Dead fish released detectable amounts of both eDNA and eRNA, indicating that eRNA-based surveys cannot fully eliminate carcass-derived signals. Arrhenius-based analysis showed that eRNA degradation was more temperature-dependent than eDNA degradation. These results suggest that eRNA may improve temporal resolution for recent organismal presence under warm conditions, whereas carcass-derived eRNA may persist under cold conditions and complicate interpretation of positive detections. Overall, eRNA may help reduce carcass-related false positives, particularly in warm conditions, but should be paired with temperature-aware sampling strategies and temporal replication during colder periods.

ecology↗

bioRxiv2026

Genetic polymorphisms in a mate choice locus are maintained by balancing selection in a wild medaka population

Sexual selection arises from individual differences in reproductive success, which can drive the maintenance of genetic polymorphisms in genes subject to balancing selection by the pleiotropic effects that trade-off between survival and reproduction. However, the extent to which sexual selection maintains genetic polymorphisms in wild populations remains unclear. Here, we explored on genomic signatures of balancing selection and selective sweep in the northern medaka, Oryzias sakaizumii in Japan by performing whole-genome resequencing of wild individuals. In addition, we re-evaluated the population genetic structure and admixture of Oryzias latipes and O. sakaizumii across the Japanese archipelago and detected genomic regions affected by introgression. Regions with signatures of selection from multiple statistics were located on eleven chromosomes. In particular, a region spanning 4.25 to 6.80 Mb on chromosome 18 showed high genetic diversity that could not be explained by sex differentiation or introgression from O. latipes in Eastern Japan. This pattern suggests that balancing selection maintains genetic polymorphisms in O. sakaizumii. Specifically, because a previously reported quantitative trait locus associated with female mating behavior overlaps with this region, we infer that sexual selection contributes to the maintenance of genetic polymorphism at this locus.

evolutionary biology↗

bioRxiv2023

Environmental DNA Reveals the Geographic Distributions of Two Eel Species, Anguilla japonica and A. marmorata, in Western Kyushu, Japan

Anguillid eels migrate thousands of kilometres from their spawning grounds, dispersing across a vast geographic area to fresh and brackish water habitats, where they settle and grow. Japanese eels (Anguilla japonica) and giant mottled eels (A. marmorata) are both found in Japan, although their distributions differ. However, details of these differences are unknown. We hypothesised that distribution patterns of Japanese and giant mottled eels must be different between and within rivers along the northwest coast of Kyushu, Japan. Environmental DNA (eDNA) analysis was conducted at 87 sites in 23 rivers. Japanese eel eDNA was detected in 19 rivers (82.6%) and that of giant mottled eels was detected in 8 (34.8%). eDNA for Japanese eels was detected at 6 of 9 sites in the North (66.7%), 13 of 23 sites in Omura (56.5%) and 37 of 55 sites in the South (67.3%). In contrast, giant mottled eel eDNA was detected at 1 of 9 sites in the North (11.1%), no sites in Omura and 15 of 55 sites in the South (27.3%). There was no correlation between eDNA concentrations of the two species at 10 sites in the five rivers where eDNA of both species was detected, implying that their habitat preference differ. This partially reveals dispersal and settlement mechanisms of these eel species.

ecology↗

bioRxiv2023

Wnt4a is indispensable for genital duct elongation but not for gonadal sex differentiation in the medaka Oryzias latipes

In most vertebrates, oviducts are derived from Mullerian ducts and sperm ducts from Wolffian ducts. In teleosts, however, Mullerian ducts are absent. Wolffian ducts function as nephric ducts in both sexes, and genital ducts are formed by posterior extension of either ovaries or testes. Whether genital ducts of teleosts are newly evolved organs or are a variant of the Mullerian ducts is an important question for evolutionary mechanisms of morphogenesis. One of the genes essential for Mullerian duct formation in mice, wnt4, is expressed in the mesenchyme and induces invagination of the coelomic epithelium and its posterior elongation. Here, we approached to the above question by examining genital duct development in mutants of two Wnt4 genes in medaka (wnt4a is orthologous to mouse wnt4 and wnt4b paralogous). The wnt4b mutants had short body but were fertile with normal genital ducts. In contrast, both male and female wnt4a mutants had posterior elongation of the gonads stopped within or just outside the coelom, depending on the mutated alleles. Genetic females of the scl mutants (unable to synthesize testosterone or estrogens) have gonads containing both previtellogenic oocytes and spermatogenic cysts. Their gonads do not have ovarian cavities or sperm duct primordia and are lacking genital ducts completely. The results suggest Wnt4a target organs are posterior parts of the ovarian cavities or the sperm duct primordia. Medaka wnt4a was expressed in the mesenchyme ventral to the genital ducts in both sexes. Thus, the aborted elongation of genital ducts in the wnt4a mutants, the ortholog of mouse wnt4, suggests strongly that mouse Mullerian ducts and teleost genital ducts share homologous developmental processes. To further demonstrate this possible homology, mechanisms of genital duct formation and possible roles of Wnt4 should be compared before and after the appearance of Mullerian ducts in vertebrate phylogeny, namely jawless fish and cartilaginous fish. Additionally, wnt4a and wnt4b single mutants or double mutants did not show sex-reversal, suggesting both genes are dispensable for gonadal sex differentiation in medaka. This is in contrast to indispensable function of Wnt4 in mammalian ovarian differentiation.

developmental biology↗