Species Of Oryzias Research Articles

Molecular phylogeny and phylogeography of ricefishes (Teleostei: Adrianichthyidae: Oryzias) in Sri Lanka.

Ricefishes of the genus Oryzias occur commonly in the fresh and brackish waters in coastal lowlands ranging from India across Southeast Asia and on to Japan. Among the three species of Oryzias recorded from peninsular India, two widespread species, O. carnaticus and O. dancena, have previously been reported from Sri Lanka based on museum specimens derived from a few scattered localities. However, members of the genus are widespread in the coastal lowlands of Sri Lanka, a continental island separated from India by the shallow Palk Strait. Although recent molecular phylogenies of Adrianichthyidae represent near‐complete taxon representation, they lack samples from Sri Lanka. Here, based on sampling at 13 locations representative of the entire geographic and climatic regions of the island's coastal lowlands, we investigate for the first time the molecular phylogenetic relationships and phylogeography of Sri Lankan Oryzias based on one nuclear and two mitochondrial markers. Sri Lankan Oryzias comprise two distinct non‐sister lineages within the javanicus species group. One of these is represented by samples exclusively from the northern parts of the island; it is recognized as O. dancena. This lineage is recovered as the sister group to the remaining species in the javanicus group. The second lineage represents a species that is widespread across the island's coastal lowlands. It is recovered as the sister group of O. javanicus and is identified as O. cf. carnaticus. Ancestral‐range estimates suggest two independent colonizations of Indian subcontinent and Sri Lanka by widespread ancestral species of Oryzias during two discrete temporal windows: late Miocene and Plio‐Pleistocene. No phylogeographic structure is apparent in Sri Lankan Oryzias, suggesting that there are no strong barriers to gene flow and dispersal along the coastal floodplains, as is the case also for other generalist freshwater fishes in the island.

Evidence for sympatric speciation in a Wallacean ancient lake.

Sympatric speciation has been demonstrated in few empirical case studies, despite intense searches, because of difficulties in testing the criteria for this mode of speciation. Here, we report a possible case of sympatric speciation in ricefishes of the genus Oryzias on Sulawesi, an island of Wallacea. Three species of Oryzias are known to be endemic to Lake Poso, an ancient tectonic lake in central Sulawesi. Phylogenetic analyses using RAD-seq-derived single nucleotide polymorphisms (SNPs) revealed that these species are monophyletic. We also found that the three species are morphologically distinguishable and clearly separated by population-structure analyses based on the SNPs, suggesting that they are reproductively isolated from each other. A mitochondrial DNA chronogram suggested that their speciation events occurred after formation of the tectonic lake, and existence of a historical allopatric phase was not supported by coalescent-based demographic inference. Demographic inference also suggested introgressive hybridization from an outgroup population. However, differential admixture among the sympatric species was not supported by any statistical tests. These results all concur with criteria necessary to demonstrate sympatric speciation. Ricefishes in this Wallacean lake provide a promising new model system for the study of sympatric speciation.

Dependence of Hainan medaka, Oryzias curvinotus (Nichols & Pope, 1927), on salinity in the Tien Yen estuary of northern Vietnam

Species of the genus Oryzias are models for studies of adaptation to osmotic environments because they demonstrate inter-species adaptability. Oryzias curvinotus, a fresh and brackish water species, is distributed from the coastal waters of southern China to northern Vietnam. The correlation of O. curvinotus’ distribution with physical water conditions in the Tien Yen estuary of northern Vietnam was recorded during monthly collections for one year. For the current study, a total of 2916 individuals of O. curvinotus were caught, of which 942 were selected to be measured and have their developmental stage recorded: 41 larvae, 749 post-larvae and 152 juveniles or adults. A developmental description and an identification to the species level are also provided. Temperature, salinity and turbidity at collection sites ranged from ca. 17 to 34°C, from ca. 0 to 16 psu and from 0 to 524 NTU, respectively. A peak catch per unit effort was found in April and at the stations at which salinity was about 0.6 to 2.5 psu. In stations where salinity was greater than 17 psu or at 0 psu, few specimens were collected. Examination of distribution indicated a tendency of the species to be present along the estuary, with the center part as the main habitat of this species. The function of an estuarine environment for fishes, which inhabit fresh and brackish waters, is discussed.

Cytochrome oxidase subunit I (COI) DNA sequence divergence between two cryptic species of Oryzias in South Korea

Oryzias latipes and Oryzias sinensis are indigenous species found in Japan, China, and other East Asian countries, including Korea. Based on morphological differences, the species have been classified distinctly. However, the range of morphological characters such as the number of gill rakers, vertebrae, and spots on the lateral body overlaps and is too vague for clear identification, so their classification based on their morphological characteristics remains uncertain. In this study, the mitochondrial cytochrome oxidase subunit I (COI) gene, which is used for DNA barcoding, was applied to clarify interspecific variation of O. latipes and O. sinensis. Intraspecific genetic diversity was calculated to identify correlations with geographic distributions. We studied two species collected from 55 locations in Korea. All individuals carried a 679-base pair gene without deletion or insertion. Between species, 525 base pairs of the gene were shared. The Kimura two parameter (K2P) distance of O. latipes and O. sinensis was 0.41% and 1.39%, respectively. Mean divergence within genera was 23.5%. Therefore, the species were clearly different. The distance between O. latipes and O. sinensis was 14.0%, which is the closest within genera. Interestingly O. latipes from the Japanese and Korean group represented 16.5% distant. These results were derived from geohistorical and anthropogenic environmental factors. The O. latipes haplotypes were joined in only one group, but O. sinensis was divided into two groups, one is found in the Han River and upper Geum River watershed; the other is found in the remaining South Korean watersheds. Further studies will address the causes for geographic speciation of O. sinensis haplotypes.

Molecular phylogeny of the medaka fishes genus Oryzias (Beloniformes: Adrianichthyidae) based on nuclear and mitochondrial DNA sequences

The phylogenetic relationships among medaka fishes of 2 genera, Oryzias and Xenopoecilus, were studied using the nuclear tyrosinase and mitochondrial 12S and 16S rRNA genes. Of the 23 species currently described for these genera, 13 species of Oryzias and 2 species of Xenopoecilus were examined. The tree topologies obtained from the nuclear and mitochondrial data were consistent, indicating that Xenopoecilus is a polyphyletic genus nested within Oryzias. This result suggested the necessity for a systematic study and taxonomic revision of Xenopoecilus. The combined data analysis of all data partitions resulted in a well-resolved tree, with most internal branches supported by high statistical values. Based on our combined data phylogeny, we divided the Oryzias species into three major species groups, namely the latipes, javanicus, and celebensis groups. These three groups corresponded to the three chromosomal groups (biarmed, monoarmed, and fused chromosome groups) previously proposed from karyological analyses. The phylogeographic pattern suggests historical vicariance between Sulawesi Island and the continental shelf.

Systematic observations on tropical Asian medakas or ricefishes of the genusOryzias, with descriptions of four new species

The so-calledOryzias melastigma (McClelland, 1839), reported from India, Bangladesh, Myanmar, and Malaysia by numerous authors beginning with Day (1877), is based mainly or entirely onAplocheilus panchax (Hamilton, 1822). India and Bangladesh have two species ofOryzias, both large. The deeper-bodied of these two species is reported for the first time asO. dancena (Hamilton, 1822). The other is identified asO. carnaticus (Jerdon, 1849). Myanmar has one large species,O. dancena, and one tiny species,O. uwai new species.Oryzias minutillus Smith, 1945 andO. uwai differ from all otherOryzias in having 4/5 instead of 5/6 principal caudal fin rays.Oryzias uwai differs fromO. minutillus in being more conspicuously pigmented and having large, 6-rayed pelvic fins often extending to anal fin origin instead of much smaller and shorter 5-rayed pelvic fins. In Thailand (including its part of the Mekong basin) three species are known: a large estuarine species tentatively identified asO. javanicus (Bleeker, 1854) and two tiny inland species,O. mekongensis Magtoon & Uwa, 1986, andO. minutillus. Oryzias minutillus from many localities are more or less melanoproctic, i.e. have a darkly pigmented genital or vent area not seen in other species. The Mekong basin in Laos has two large species,O. latipes (Temminck & Schlegel, 1846) andO. pectoralis new species, distinguished by a prominent black blotch on the pectoral fin base, both recently collected in the Nam Theun watershed in central Laos; and two tiny species,O. mekongensis andO. minutillus. Only one species ofOryzias is known from the Mekong delta in Vietnam, the small moderately deep-bodiedO. haugiangensis new species, with 19–22 anal and 9–10 pectoral fin rays. The Indonesian island of Java has one large species,O. javanicus (Bleeker, 1852) with 21–25 anal and 11 pectoral fin rays, and one small species,O. hubbsi new species, with only 17–21 anal and 9 pectoral fin rays.

Identification of the sex chromosomes of the medaka, Oryzias latipes, by fluorescence in situ hybridization

In the medaka, Oryzias latipes, which does not have cytologically recognizable sex chromosomes, the sex is genetically determined and the mechanism of sex determination (XX/XY) can be revealed by genetic crosses using a particular pigment gene. In a previous study, we isolated a sex-linked DNA marker (SL1) using the genomic differences between inbred strains of medaka. In the present paper, we further isolated another sex-linked clone (pHO5.110). The pHO5.110-related sequences were tightly linked to sex in O. latipes. We designated the locus of the pHO5.110-related sequence on sex chromosomes of medaka as Sex-Linked 2 (SL2). Southern blot analyses suggested that the pHO5.110-related sequence was tandemly repetitive in the medaka genome. Using the clone as a probe for FISH analysis, strong hybridization signals were obtained in a couple of chromosomes that formed one of two large submetacentric chromosome pairs. The pHO5.110-related sequences were repetitive in the genomes of other species of Oryzias (O. curvinotus, O. luzonensis and O. mekongensis) that are karyologically related to O. latipes (all are members of the so-called biarmed group). By contrast, the sequences were not detected as repetitive in other Oryzias species. Hence, it is thought that pHO5.110-related sequences were amplified in the genome of a common ancestor of the biarmed group.

Cloning and characterization of cDNAs for 70-kDa heat-shock proteins (Hsp70) from two fish species of the genus Oryzias.

cDNA corresponding to two hsp70-related genes (OLHSC70 and CEHSC70) were isolated from two lines of cultured fish cells derived from the genus Oryzias. OLHSC70 was 2,261 bp in length and encoded a protein of 686 amino acids with a predicted molecular mass of 76,120 daltons. CEHSC70 was 2,114 bp in length and it lacked the 5' region found in OLHSC70. Two-dimensional electrophoresis revealed that Oryzias latipes has at least three heat-inducible proteins with molecular masses of about 70,000 daltons. One of these proteins (Hsp70.1) was barely expressed under normal conditions but its high-level expression was induced by hyperthermia. The other two proteins (Hsc70.1, and Hsc70.2) were constitutively expressed under normal conditions and only slightly enhanced levels were induced by hyperthermia. Transfection with the cloned sequence, RNA dot-blot analysis and the two-dimensional electrophoresis of proteins showed that OLHSC70 encoded Hsc70.1.

Cloning and characterization of cDNAs for 70-kDa heat-shock proteins (Hsp70) from two fish species of the genus Oryzias

Cloning and characterization of cDNAs for 70-kDa heat-shock proteins (Hsp70) from two fish species of the genus Oryzias

Relationship between the induction of proteins in the HSP70 family and thermosensitivity in two species of Oryzias (Pisces)

A cultured fish cell line, CE, derived from Oryzias celebensis, which lives in a tropical zone, was more heat-resistant than the OL32, which were derived from the Japanese medaka, Oryzias latipes which lives in a temperate zone. Protein synthesis in OL32 cells was also more heat-sensitive than that in CE cells. The relative levels in proteins of the HSP70 family and the ability of cells to tolerate severe heat treatment after a conditioning heat treatment were examined. Twenty-four hours after conditioning heat treatment, both cell lines retained thermotolerance even though three proteins in the HSP70 family had returned to their control levels.

Inter‐ and intraspecific distribution of an antigenic epitope found in an inbred strain of the Medaka, Oryzias latipes

AbstractWe attempted to produce monoclonal antibodies against strain‐specific antigens of the Medaka, Oryzias latipes, using eight inbred strains and several wild populations. One monoclonal antibody, named m11C1, showed reactivity to the cells of one inbred strain HB11C but not to the cells of the other inbred strain HNI. The reactivity was also found for the cells of four other inbred strains but not to that for two inbred strains. To understand the character of the antigen recognized by the m11C1, wer examined wild populations of the Medaka in regard to reactivity for the m11C1. Among fish collected from 122 localities, the m11C1 exclusively recognized the cells of the fish which were classified as the Southern Population. None of the fish from the Northern, the East Korean, and the China‐West Korean Populations reacted with the m11C1 antibody. Thus, the antigen recognized by the m11C1 was named SA1 (Southern Population‐specific Antigen 1). The SA1 antigen from liver cells appeared as a single band on Western blot with a molecular mass of 31 kDa. This antigen mainly localized in epithelia of intestinal vili and in melano‐macrophages which were frequently observed in spleen and anterior kidney. Genetic corsses suggested that SA1‐positive phenotype was dominant. Moreover, SA1 was also detected in two closely related species, O. luzonensis and O. curvinotus, but not in less‐ related five species of the genus Oryzias. Origin and propagation of the SA1 antigen were discussed based on geographic and phylogenic distribution pattern of SA1. © 1993 Wiley‐Liss, Inc.

Electrophoretic studies of meiotic segregation in inter‐ and intraspecific hybrids among East Asian species of the genus Oryzias (Pisces: Oryziatidae)

AbstractThree species of Oryzias, namely, O. curvinotus, O. luzonensis, and four subspecific groups of O. latipes, have been found in East Asia. In order to elucidate the genetic relationships among theses species, fertility and meiotic segregation in hybrids were examined. Fertile males and females and normal segregation were observed in intraspecific crosses of O. latipes and in interspecific hybrids between O. luzonensis and O. curvinotus. By contrast, male sterility and production of non‐reductional 2nd eggs by female were observed in interspecific crosses between O. latipes and O. curvinotus. Similar results were obtained with luzonensis‐latipes hybrids. These results demonstrated that O. luzonensis and O. curvinotus are closely related, and that reproductive isolation is complete between O. latipes and O. luzonensis and between O. latipes and O. curvinotus. © 1992 Wiley‐Liss, Inc.

メダカ完全異質三倍体の作成

Hybrid females between Oryzias latipes sinensis and O. curvinotus lay non-reductional diploid eggs. We tried to produce trigenomic allotriploid medaka by fertilizing the diploid eggs with the sperm of three different species of Oryzias, O. celebensis, O. melastigma, and O. javanicus. Viable offspring were obtained when the eggs were inseminated by O. celebensis. Karyotype analysis confirmed that these fish were trigenomic allotriploids with three different genomes from O. latipes sinensis, O. curvinotus, and O. celebensis. Electrophoretic patterns of proteins (soluble muscle protein and eight isozymes) of these trigenomic allotriploids showed a normal expression of genes from these three genomes.

Species-specific expression of parvalbumins in the genus Oryzias and its related species

1. 1. Several species-specific proteins were identified by polyacrylamide gel electrophoresis of skeletal muscle extracts from five species of Oryzias. 2. 2. The diffuse appearance, rapid anodal mobility, and low mol. wt suggested that these proteins belong to calcium-binding protein or parvalbumin class. 3. 3. Immunochemical studies indicated that five components in three distinct zones had common antigenic property in part and could be divided into two types. 4. 4. The application of parvalbumins to systematic studies and the evolution of this class of proteins of cyprinodont fishes were discussed.

Comparison of cold, heat and radiation sensitivities of the fish embryos among the genus Oryzias

Abstract 1. 1. Cold, heat and radiation sensitivities of fish embryos in three species of the genus Oryzias were compared and developmental changes in these sensitivities were also examined. 2. 2. Cold resistance of the embryos correlated with the species' geographical distribution. 3. 3. Heat sensitivity, in contrast, did not necessarily correlate with the temperature of these species' habitats. 4. 4. There was no correlation between the heat sensitivity and radiosensitivity. 5. 5. The rate of induced thermotolerance, reflected by TTR (thermotolerance ratio) values, was almost the same regardless of the species and developmental stages, indicating that the TTR value is independent of primary thermal resistance of the animals.