The Japanese wild population of the medaka fish (Oryzias latipes species complex) comprises two genetically distinct groups, the Northern and the Southern Populations, with boundary populations having a unique genotype. It is thought that the boundary populations have been formed through introgressive hybridization between the two groups, because they are fixed with the Northern alleles at two allozymic loci, with the Southern alleles at two other loci, and have a unique allele at one locus. In this study, we examined the genetic population structure of the boundary populations using genome-wide single nucleotide polymorphism (SNP) data. Most SNPs of the Toyooka population, a typical boundary population, were shared with the Northern Population, some were shared with the Southern Population, and the remaining SNPs were unique to this population, suggesting that the boundary populations originated and diverged from the Northern Population. Further analyses of different populations using SNPs at eight genomic loci indicated that the boundary populations at different locations share similar genomic constitutions, and can be genetically distinguished from typical Northern Populations by unique SNPs. In addition, the boundary populations in the Maruyama River Basin had Northern mitochondrial DNA (mtDNA), while others, from the Fukuda and Kishida River Basins and from the Kumihama Bay area, had Southern mtDNA. These findings suggested that the boundary populations originated from the Northern Population, and then their genomes diverged as a result of geographical isolation, followed by mtDNA introgression from the Southern Population that occurred independently in some populations.

We analyzed geographic variation in skull morphology of the large Japanese field mouse (Apodemus speciosus) and determined changes in skull morphology that occurred during the evolutionary history of A. speciosus in relation to the estimated distribution range in the last glacial maximum (LGM). We analyzed 1,416 specimens from 78 localities using geometric morphometric techniques applied to the dorsal side of the cranium and mandible. While large variations within and among the populations in Honshu, Shikoku, and Kyushu were observed, geographic patterns were not observed. Hokkaido and peripheral island populations showed shared differentiation from the Honshu, Shikoku, and Kyushu populations with a larger skull and distinct mandible shape. In addition, these two groups also differed from each other in accumulated random shape variation. Common characteristics found in Hokkaido and peripheral island populations were considered to be the ancestral states, which were retained by geographic isolation from the main islands. Random variations in Hokkaido and the peripheral island populations were formed through stochastic processes in relation to their isolation. Characteristic morphologies widely found in the populations of Honshu, Shikoku, and Kyushu were considered to be derived states that expanded after separation from the peripheral islands. Complex geomorphology and a shift in distribution range related to climate change and altitudinal distribution are suggested to have formed the complex geographic variation in this species.

The Ogasawara Archipelago comprises two groups of oceanic islands: the Bonin Islands, formed in the Paleogene, and the Volcano Islands, formed in the Quaternary. These groups are located within a moderate distance (ca. 160–270 km) of one another; thus, most land bird species are not distinguished as different subspecies. Two land birds, however, show unusual distribution. The Japanese white-eyes Zosterops japonicus originally inhabited only the Volcano Islands, but has been introduced to the Bonin Islands. The brown-eared bulbuls Hypsipetes amaurotis are distributed as a different subspecies. We investigated their genetic differences and divergences in the Ogasawara Archipelago using mitochondria DNA. The Volcano population of white-eyes had four endemic haplotypes that were divergent from one another, except for the Bonin population, which shared three haplotypes with the Volcano, Izu, and Ryukyu Islands and did not have any endemic haplotype. This is the first genetic suggestion that the Bonin population is a hybrid of introduced populations. With respect to bulbuls, the Volcano and Bonin Islands each had a single endemic haplotype. The Volcano haplotype is closest to a haplotype shared with Izu, the Japanese mainland, Daito and Ryukyu, whereas the Bonin haplotype is closest to one endemic to the south Ryukyu Islands. This indicates that the sources of the two bulbul populations can be geologically and temporally distinguished. The populations of the two species in the Ogasawara Archipelago are irreplaceable, owing to their genetic differences and should be regarded as evolutionarily significant units. In order to prevent introgression between the two populations, we must restrict interisland transfers.

The distribution of the branchiobdellidan Holtodrilus truncatus (Liang, 1963), which is symbiotic on atyid shrimps, was surveyed in 26 river catchments, covering almost all of the Kii Peninsula, western Japan. Holtodrilus truncatus has been recorded in 10 rivers located from the southwest to northeast regions of the peninsula. Paratya compressa was the dominant host species in all rivers, with a lower prevalence on Caridina leucosticta, C. multidentata, C. typus, and Neocaridina denticulata. The longitudinal distribution of H. truncatus was limited to the middle and upper reaches, while its main host P. compressa occurred widely from the lower to the upper reaches. The numbers of H. truncatus and their cocoons per host increased in summer and decreased in winter, in accordance with the abundance of the host P. compressa. The body size of P. compressa was larger in individuals with H. truncatus than those without H. truncatus in some rivers, while in another river, sizes of the two groups were not different. A salinity tolerance experiment revealed that the threshold of salinity tolerance of H. truncatus occurred between 0-0.5%. A choice experiment between two host species showed that H. truncatus preferred C. leucosticta to C. multidentata, P. compressa to C. multidentata, and P. compressa to C. leucosticta.

We used previously established molecular methods to determine how far the Asian invader nereidid worm Hediste diadroma has spread into northeast Pacific estuaries that are inhabited by the native congener H. limnicola. Further, we analyzed the mitochondrial DNA of 702 Hediste specimens collected from 27 estuaries along 1,350 km of coastline in Washington, Oregon, and California, USA, to distinguish between the morphologically indistinguishable immature stages of these two species. In total, 377 specimens were identified as the invader H. diadroma and 325 were identified as the native H. limnicola. The invader H. diadroma was dominant at many sites in Puget Sound, Washington, and in the Columbia River estuary, Washington, and Oregon, suggesting that this species initially invaded estuaries in Washington or northern Oregon. In contrast, the native H. limnicola was dominant at intertidal sites in California and at subtidal sites in the Columbia River estuary. We also analyzed a partial nucleotide sequence from the mitochondrial cytochrome oxidase subunit I gene of H. diadroma in specimens collected from seven sites in the US and 11 sites in Japan, which showed no marked geographic differentiation between 18 US and 31 Japanese haplotypes. This finding suggests that H. diadroma have been introduced repeatedly into US estuaries from many regions in Japan.

Adipose tissue is a lipid storage organ characterized by the pronounced accumulation of adipocytes. Although adipose tissues are found in various parts of the vertebrate body, it is unclear whether these tissues have a common ancestral origin or have evolved in several phylogenetic lineages by independent adipocyte accumulation events. To gain insight into the evolutionary history of vertebrate adipose tissues, we determined the distribution of adipocytes by oil red O staining in skeletal muscle of 10 teleost species spanning eight orders: Tetraodontiformes, Pleuronectiformes, Spariformes, Salmoniformes, Clupeiformes, Beloniformes, Osmeriformes, and Cypriniformes. Accumulation of adipocytes in the myoseptum was observed in many species, including red seabream, rainbow trout, Pacific herring, Pacific saury, zebrafish and giant danio. We also found some order-, species-, and swimming mode-specific distribution patterns of adipocytes: 1) almost complete absence of intramuscular adipocytes in the order Tetraodontiformes (torafugu and spotted green pufferfish), 2) clear adipocyte accumulation in the inclinator muscles of fin in Japanese flounder, 3) a large intramuscular adipose tissue at the root of the dorsal fin in ayu, and 4) thick lipid layers consisting of subcutaneous adipose tissue and red muscle lipids in pelagic migratory fish (Pacific herring and Pacific saury). Of note, Pacific herring and Pacific saury are phylogenetically distinct species sharing a similar niche and swimming mode, suggesting that their analogous adipocyte/lipid distribution patterns are the consequence of convergent evolution. The potentially heterogeneous origin of adipose tissues has significant implications for the interpretation of their functional diversity.

With the aim of exploring phylogenetic relationships within Cypridoidea, the most species-rich superfamily among the podocopidan ostracods, we sequenced nearly the entire 18S rRNA gene (18S) and part of the 28S rRNA gene (28S) for 22 species in the order Podocopida, with representatives from all the major cypridoid families. We conducted phylogenetic analyses using the methods of maximum likelihood, minimum evolution, and Bayesian analysis. Our analyses showed monophyly for Cyprididae, one of the four families currently recognized in Cypridoidea. Candonidae turned out to be paraphyletic, and included three clades corresponding to the subfamilies Candoninae, Paracypridinae, and Cyclocypridinae. We propose restricting the name Candonidae s. str. to comprise what is now Candoninae, and raising Paracypridinae and Cyclocyprininae to family rank within the superfamily Cypridoidea.

Amphibians are highly susceptible to environmental changes, mainly at the larval stage during which they are restricted to small and ephemeral aquatic habitats, which are subject to large fluctuations of abiotic parameters, such as temperature and pH. Consequently, tadpoles experience changes in biochemical, physiological, and molecular processes related to the maintenance of homeostasis, which may lead them to an oxidative stress state. In the present study, we investigated the effects of stress caused by changes in temperature and pH on the antioxidant enzymes catalase (CAT), glucose-6-phosphate dehydrogenase (G6PDH), glutathione reductase (GR) and glutathione-S-transferase (GST) in tadpoles of Eupemphix nattereri. The results show that changes in temperature and pH conditions induce an antioxidant response in tadpoles. GST and GR showed temperature-dependent activities; GST activity was higher in tadpoles exposed to 28°C, whereas GR exhibited increased activity in response to 28°C and 36°C. At 32°C, both GST and GR had the lowest activity. CAT was induced by treatments with acidic (pH 5.0) and alkaline (pH 8.5) pH. Tadpoles exposed to acidic pH also had increased GR activity. The G6PDH was not changed in either experiment. Our data demonstrate that E. nattereri possesses an efficient antioxidant defense system for coping with the damaging effects of heat and acidity/alkalinity conditions in water. The alterations in antioxidant enzymes are probably a result of immediate physiological adaptation of individuals in response to increased production of ROS under environmental stress conditions.

We used a differential display in combination with complementary DNA (cDNA) cloning approach to isolate a novel rat gene LOC690919 with an open reading frame of 1227-length nucleotides encoding a protein of 409 amino acids. This gene was designated as Spergen-4 (a spermatogenic cell-specific gene-4). Spergen-4 mRNA was highly expressed in testis, and its expression was detected in rat testis starting at three weeks of postnatal development and persisting up to adulthood. Mouse and human orthologs, which lack N-terminal 77 amino acid residues of rat Spegen-4, were found in the database. Immunofluorescence microscopy and immunoblot analysis demonstrated that Spergen-4 was not expressed in spermatogonia, spermatocytes, and round spermatids, but was restrictedly detected at sperm head, cytoplasm, and developing flagella of elongated spermatids in rat testis. In mature spermatozoa, Spergen-4 was detected at the acrosome region as well as the principal piece of flagella. Spergen-4 immunosignal disappeared from sperm heads on acrosome reaction induced by progesterone. These data suggest that Spergen-4 integrated into elongated spermatids during spermiogenesis serves as a constituent for acrosome region and flagella of rat spermatozoa.

The rhizocephalan Sacculina shiinoi sp. nov. parasitizes three species of Upogebia in Japan. It is described morphologically and compared with another Upogebia parasite, Sacculina upogebiae Shiino, 1943 from Japan and Korea. These two species are the only sacculinids that parasitize mud shrimps. DNA analyses clearly show the two species to be separate and not closely related. The cuticle differs in being provided with close-set, branched, and spiny excrescences in S. shiinoi, while it lacks excrescences, but forms small scales in S. upogebiae. In S. upogebiae, the bulbous sperm-producing part and the narrow receptacle duct are separated by a compartmentalized mid portion, which is missing in S. shiinoi. A ridge, having a thickened, fluffy cuticle with a U-shaped course, passes across the visceral mass between the two receptacle openings in S. shiinoi. Such a structure has never been described in other rhizocephalans, and its function is uncertain.