Evolutionary patterns of shape and functional diversification in the skull and jaw musculature of triggerfishes (Teleostei: Balistidae)

The robust skull and highly subdivided adductor mandibulae muscles of triggerfishes provide an excellent system within which to analyze the evolutionary processes underlying phenotypic diversification. We surveyed the anatomical diversity of balistid jaws using Procrustes‐based geometric morphometric analyses and a phylomorphospace approach to quantifying morphological transformation through evolution. We hypothesized that metrics of interspecific cranial shape would reveal patterns of phylogenetic diversification that are congruent with functional and ecological transformation. Morphological landmarks outlining skull and adductor mandibulae muscle shape were collected from 27 triggerfish species. Procrustes‐transformed skull shape configurations revealed significant phylogenetic and size‐influenced structure. Phylomorphospace plots of cranial shape diversity reveal groupings of shape between different species of triggerfish that are mostly consistent with phylogenetic relatedness. Repeated instances of convergence upon similar cranial shape by genetically disparate taxa are likely due to the functional demands of shared specialized dietary habits. This study shows that the diversification of triggerfish skulls occurs via modifications of cranial silhouette and the positioning of subdivided jaw adductor muscles. Using the morphometric data collected here as input to a biomechanical model of triggerfish jaw function, we find that subdivided jaw adductors, in conjunction with a unique cranial skeleton, have direct biomechanical consequences that are not always congruent with phylomorphospace patterns in the triggerfish lineage. The integration of geometric morphometrics with biomechanical modeling in a phylogenetic context provides novel insight into the evolutionary patterns and ecological role of muscle subdivisions in triggerfishes. J. Morphol. 277:737–752, 2016. © 2016 Wiley Periodicals, Inc.     

Functional morphology of digestion in the stomachless,piscivorous needlefishes Tylosurus gavialoides and Strongylura leiura ferox (Teleostei: Beloniformes)

Belonidae are unusual in that they are carnivorous but lack a stomach and have a straight, short gut. To develop a functional morphological model for this unusual system the gut contents and alimentary tract morphology of Tylosurus gavialoides and Strongylura leiura ferox were investigated. The posterior orientation of the majority of the pharyngeal teeth supports the swallowing of whole large prey, but not their mastication. Mucogenic cells are abundant in the mucosa lining, particularly the esophagus, and their secretions are likely to protect the gut lining from damage while lubricating passage of the prey. Esophagus, anterior intestine, posterior intestine, and rectum all have highly reticulate mucosae. The anterior three gut sections are distensible to accommodate the passage of prey. However, following ingestion large prey are passed to the highly distensible posterior intestine where they rest head first against the ileorectal valve. Alimentary pH ranges from neutral to weakly acidic. Fish prey is digested head first with the head being largely digested while the remainder of the body is still intact. The nondistensibility of the rectum and the small aperture provided by the ileorectal valve suggest the products of intestinal digestion are either small particulates or fluids that pass into rectum where they are absorbed. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Phylogeny of the flyingfish family Exocoetidae (Teleostei, Beloniformes)

The phylogeny of the flyingfish family Exocoetidae is studied cladistically, using 41 morphological characters encompassing early life history, and external and internal features. The monophyly of the family is supported by 10 synapomorphies. Within the family,Oxyporhamphus is the sister group to all other genera, the monophyly of the latter being defined by 10 synapomorphies.Fodiator is the sister group of genera characterized by the presence of chin barbels in juveniles.Parexocoetus is the sister group ofExocoetus, Cypselurus, Prognichthys andHirundichthys, the latter being defined by four synapomorphies. In the latter group,Exocoetus is the sister group of the other three genera. The phylogeny of the Exocoetidae is characterized by the stepwise upgrading of gliding capability, with sequential modifications of the caudal, pectoral and pelvic fins. The subfamily Oxyporhamphinae is resurrected.     

Modulation of ethanol toxicity by Asian ginseng (Panax ginseng) in Japanese ricefish (Oryzias latipes) embryogenesis

Alcohol consumption by women during pregnancy often induces fetal alcohol spectrum disorder (FASD) in children who have serious central nervous system (CNS), cardiovascular, and craniofacial defects. Prevention of FASD, other than women abstaining from alcohol drinking during pregnancy, is not known. A limitation of the use of synthetic anti-alcoholic drugs during pregnancy led us to investigate herbal products. In particular, many plants including Asian ginseng (Panax ginseng) have therapeutic potential for the treatment of alcoholism. We used Japanese ricefish (medaka) (Oryzias latipes), an animal model of FASD, for identifying herbal medicines that can attenuate ethanol toxicity. Fertilized eggs in standard laboratory conditions were exposed to ginseng (PG) root extract (0–2 mg/mL) either 0–2 (group A) or 1–3 (group B) day post fertilization (dpf) followed by maintenance in a clean hatching solution. The calculated IC₅₀ as determined 10 dpf in A and B groups were 355.3 ± 1.12 and 679.7 ± 1.6 μg/mL, respectively. Simultaneous exposure of embryos in sub-lethal concentrations of PG (50–200 μg/mL) and ethanol (300 mM) for 48 h disrupted vessel circulation and enhanced mortality. However, PG (100 μg/mL) may partially protect trabecular cartilage (TC) deformities in the neurocranium in B group embryos induced by ethanol (300 mM). To understand the mechanism, embryonic ethanol concentration was measured at 2 dpf and adh5, adh8, aldh2, aldh9a, catalase, GST, and GR mRNAs were analyzed at 6 dpf. It was observed that although ethanol is able to reduce adh8 and GST mRNA contents, the simultaneous addition of PG was unable to alter ethanol level as well as mRNA contents in these embryos. Therefore, antagonistic effects of PG on ethanol toxicity are mediated by a mechanism which is different from those regulating ethanol metabolism and oxidative stress.     

Complete mitogenome sequence of the Chinese medaka Oryzias sinensis (Teleostei: Beloniformes) and its phylogenetic analysis

Chinese medaka Oryzias sinensis (Teleostei: Beloniformes) is distributed in China and the western areas of Korea. It differs from the Japanese medaka O. latipes in its morphology and biogeographical distribution in Korea. In this study, we analyzed the complete nucleotide sequence of the mitochondrial genome (mitogenome) of O. sinensis and determined its genomic structure. The complete mitogenome is a circular molecule of 16,654 bp and its structural organization is conserved across diverse vertebrate taxa. On a phylogenetic tree inferred from the nucleotide matrix, partitioned into four regions (i.e., the first and second codon positions of protein-coding genes, and the ribosomal RNA and transfer RNA genes), O. sinensis clustered consistently with O. latipes specimens from China and Korea, with a relatively short branch length, but was separated from O. latipes specimen from Japan. Our findings will allow the resolution of the taxonomic problems of closely related Oryzias species, such as O. sinensis and O. latipes in a future study.     

A phylogenetic analysis and taxonomic revision of ricefishes,Oryzias and relatives (Beloniformes,Adrianichthyidae)

Ricefishes, known best by the model organism, the medaka, Oryzias latipes Temminck & Schlegel, 1846, comprise the family Adrianichthyidae, which ranges broadly throughout fresh and brackish waters of Central, South and Southeast Asia and the Indo‐Malay‐Philippines Archipelago as far east as Timor. Twenty‐eight Recent species are recognized here in two monophyletic genera, Adrianichthys and Oryzias. Xenopoecilus and Horaichthys are placed in synonymy of Oryzias for the first time. Adrianichthys comprises four species from Lake Poso, Sulawesi, Indonesia. Oryzias comprises 24 species that live throughout the range of the family. A fossil genus and species, ?Lithopoecilus brouweri from the Miocene of central Sulawesi, is included tentatively in the Adrianichthyidae. Evidence for the sister group relationship of adrianichthyids and exocoetoids is reviewed briefly and that relationship corroborated. Monophyly of adrianichthyids is likewise strongly supported here. Species groups within Oryzias are diagnosed as monophyletic largely based on osteology, colour pattern and meristic variation. They correspond only in part to species groups previously recognized based on chromosome constitution. Miniature species do not comprise a monophyletic group; disjunct absolute size in close relatives has evolved repeatedly. Oryzias latipes is a member of a species complex that includes O. luzonensis, O. curvinotus and the miniatures O. sinensis and O. mekongensis. A new species, Oryzias bonneorum sp. nov. , is described from Lake Lindu, Sulawesi, Indonesia. Lectotypes are designated for Haplochilus celebensis Weber, 1894 and Haplochilus timorensis Weber & de Beaufort, 1922. No claim to original US Government works. Journal compilation © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154 , 494–610.     

Japanese medaka (Oryzias latipes): developmental model for the study of alcohol teratology

BACKGROUND: Animal models are necessary to investigate the mechanism of alcohol-induced birth defects. We have used Japanese medaka (Oryzias latipes) as a non-mammalian model to elucidate the molecular mechanism(s) of ethanol teratogenesis. METHODS: Medaka eggs, within 1 hr post-fertilization (hpf) were exposed to waterborne ethanol (0-1000 mM) in hatching solution for 48 hr. Embryo development was observed daily until 10 days post-fertilization (dpf). The concentration of embryonic ethanol was determined enzymatically. Cartilage and bones were stained by Alcian blue and calcein, respectively and skeletal and cardiovascular defects were assessed microscopically. Genetic gender of the embryos was determined by PCR. Levels of two isoenzymes of alcohol dehydrogenase (Adh) mRNAs were determined by semi-quantitative and real-time RT-PCR. RESULTS: The concentration of ethanol required to cause 50% mortality (LC50) in 10 dpf embryos was 568 mM, however, the embryo absorbed only 15-20% of the waterborne ethanol at all ethanol concentrations. The length of the lower jaw and calcification in tail fin cartilaginous structures were reduced by ethanol exposure. Active blood circulation was exhibited at 50+ hpf in embryos treated with 0-100 mM ethanol; active circulation was delayed and blood clots developed in embryos treated with 200-400 mM ethanol. The deleterious effects of ethanol were not gender-specific. Moreover, ethanol treatment was unable to alter the constitutive expression of either Adh5 or Adh8 mRNA in the medaka embryo. CONCLUSIONS: Preliminary results suggested that embryogenesis in medaka was significantly affected by ethanol exposure. Phenotypic features normally associated with ethanol exposure were similar to that observed in mammalian models of fetal alcohol syndrome. The results further indicated that medaka embryogenesis might be used as an alternative non-mammalian model for investigating specific alterations in gene expression as a means to understand the molecular mechanism(s) of ethanol-induced birth defects.     

Valproate-induced teratogenesis in Japanese rice fish (Oryzias latipes) embryogenesis

Fertilized eggs of Japanese rice fish (medaka) at three developmental stages (Iwamatsu stages 4-30) were exposed to waterborne valproic acid (VPA) (0-80 mM) in hatching solution for 48 h. The amount of valproate to cause 50% mortality (IC(50)) is found to be developmental stage-specific. The embryos were more sensitive to valproate at early stages of development (Iwamatsu stages 4-10) than in the embryos in late stages (Iwamatsu stages 17-30). Valproate exposed embryos have microcephaly and disrupted cardiovasculature with delayed vessel circulation, thrombus formation, and slow heart rate. The hatching efficiency is also reduced by valproate exposure due to developmental delay. The mRNA analysis of nine genes belong to oxidative stress (catalase, gsr, gst), neurogenesis (iro3, wnt1, shh, otx2, nlgn3b) and cell cycle regulation (ccna2) have been done. It was observed that the genes belong to oxidative stress remained unaltered after valproate exposure. However, some of the genes belong to neurogenesis (wnt1,shh, otx2 and nlgn3b) and cell cycle (ccna2) showed developmental stage-specific alteration after valproate exposure. This study indicates that valproate is able to induce some of the phenotypic features which are analogous to human fetal valproate syndrome (FVS). Modulation of genes expressed in neural tissues indicates that this fish can be used to analyze the mechanisms of many neurobehavioral disorders like Autism spectrum disorder (ASD) in human.     

Effects of pentachlorophenol on the reproduction of Japanese medaka (Oryzias latipes)

Pentachlorophenol (PCP) is widely used to control termites and protect wood from fungal-rot and wood-boring insects, and is often detected in the aquatic environment. Few studies have evaluated PCP as an environmental endocrine disruptor. In the present work, Japanese medaka (Oryzias latipes) was exposed to PCP for 28 days (F0 generation) with subsequent measurements of vitellogenin (VTG), hepatic 7-ethoxyresorufin-O-deethylase (EROD), and reproductive endpoints. Plasma VTG significantly increased in male fish treated with PCP concentrations lower than 200 microg/l and decreased in male and female animals exposed to 200 microg/l. Hepatic EROD from female fish increased when PCP exposure concentrations exceeded 20 microg/l, but decreased in the 200 microg/l PCP treatment group. Fecundity and mean fertility of female medaka decreased significantly in the second and third week following exposure concentrations greater than 100 microg/l, and testis-ova of male medaka was observed at PCP concentrations greater than 50 microg/l. Histological lesions of liver and kidney occurred when exposure concentrations exceeded 50 microg/l. In F1 generations, the hatching rates and time to hatch of offspring were significantly affected in fish exposed to 200 microg/l. These results indicated that PCP exposure caused responses consistent with estrogen and aryl hydrocarbon receptor activation as well as reproductive impairment at environmentally relevant concentrations.     

Ultrastructure of the osteogenesis of acellular vertebral bone in the Japanese medaka, Oryzias latipes (Teleostei, Cyprinidontidae)

An ultrastructural study by transmission electron microscopy (TEM) of the vertebrae of embryonic, larval, juvenile and mature medaka shows that each vertebra consists of a core of notochordal cells surrounded by a sheath of bone. The vertebral bone lacks either fully or partially embedded cells in the matrix throughout development. Bone matrix is secreted by a layer of cells that lies over the outer surface of the vertebral bone. During the early stages of osteogenesis, these cells secrete bone matrix all around themselves. However, because of the gradual flow of the newly synthesized bone matrix through intercellular spaces, matrix-producing cells do not become trapped in their own secretion. In later stages of osteogenesis, these cells secrete matrix only toward the already-deposited bone. This polarized matrix secretion allows the osteoblasts to stay always on the bone surface and never to become trapped in the matrix as osteocytes.     

Characterization of the estrogenic response to genistein in Japanese medaka (Oryzias latipes)

This study was designed to determine the estrogenic effect of the phytoestrogen genistein on several measures of endocrine function in adult Japanese medaka (Oryzias latipes) relative to 17-beta-estradiol. Adult animals of both sexes were exposed to 75, 750 and 30,000 ng/fish (average fish weight equals 0.26 g) of genistein by i.p. injection, with a positive control group treated with 300 ng/fish of 17-beta-estradiol, while a negative control group received a vehicle-only (corn oil) injection. Content of vitellogenin, the yolk glycoprotein made in the liver in response to estradiol stimulation, was measured using Western blots. Circulating estradiol and testosterone levels were measured using a steroid-enzyme immunosorbant assay. The ability of ovaries and testes to synthesize and release estradiol and testosterone was determined by ex vivo incubation of gonads with 25-hydroxycholesterol. Vitellogenin, while induced by 17-beta-estradiol, was not increased in the liver of individuals treated with genistein. In females, genistein treatment at 750 and 30,000 ng increased the estradiol production of ovaries more than the 17-beta-estradiol treatment. In males, genistein treatment resulted in decreased testosterone production from ex vivo testis and a comparable reduction in circulating testosterone level. The changes in vitellogenin, circulating steroids and ex vivo steroidogenesis in medaka in response to genistein are similar to that of 17-beta-estradiol. However, some endpoints are more sensitive to estradiol treatment (vitellogenin), while others are more sensitive to genistein (male testosterone and ovarian estrogenesis).     

The development of acellularity of the vertebral bone of the Japanese medaka,Oryzias latipes (Teleostei; Cyprinidontidae)

Among vertebrates, some teleosts are unique in having bone which lacks osteocytes embedded in the matrix. The fate of cells that secrete the matrix of these acellular bones has not been investigated thoroughly. Histological and fluorescent microscopic analysis of the vertebral bone of Oryzias latipes demonstrated that acellularity is not a secondary appearance of an early cellular bone during ontogeny. Vertebral bone is devoid of cells embedded in the matrix throughout development. Cells that secrete bone matrix do not become trapped in their own secretion. Instead, they always remain as a surface layer over the outer surface of the bone. Fluorescent microscopic visualization of tetracycline injected into growing fish demonstrated that bone was only deposited by osteoblasts lining the outer surface of the bone; no deposition of bone took place on the inner surface.