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PubMed2001

Xiphophorus genetic linkage map: beginnings of comparative gene mapping in fishes.

The explosive expansion of gene maps of mouse and man has provided strong support for hypotheses first advanced from comparing fish and mammalian genomes that the vertebrate genome was derived from multiple ancestral tetraploidizations with subsequent preferential translocations among paralogous chromosomes. At least two genome duplication events have become widely accepted in lineages leading to vertebrates, and a third has been proposed either before, or after, divergence of fishes and tetrapods. Cytogenetic and comparative gene mapping studies suggest that teleost gene maps have diverged more slowly from gene arrangements in the vertebrate ancestor than have those of mammals. The recent assembly of extensive maps of >100 genes in three fish species, medaka (Beloniformes), Xiphophorus swordtails and platyfishes (Cyprinodontiformes), and zebrafish (Cypriniformes) and the development of less extensive maps in several other fish orders provides the first salient opportunity to assess homology of most or all chromosomes among fishes.

Journal Article↗

PubMed2006

Molecular systematics of Hispaniolan pupfishes (Cyprinodontidae: Cyprinodon): implications for the biogeography of insular Caribbean fishes.

We used sequence variation in the mtDNA control-region and ND2 and cyt b genes to assess the systematics and biogeography of the five species of pupfish (Cyprinodon) on Hispaniola. These include four endemics, the relatively large-bodied Cyprinodon bondi, Cyprinodon nichollsi, and Cyprinodon sp., each from a separate lake in southwestern Hispaniola, and Cyprinodon higuey from a coastal lake in eastern Hispaniola. The fifth species consists of coastal populations referable to Cyprinodon variegatus riverendi. The results indicate that Hispaniola has been invaded by at least two forms, first by a late Pliocene progenitor of Cyprinodon variegatus ovinus and the large-bodied Hispaniolan species, and, more recently, by one or more ancestral forms allied with Cyprinodon variegatus variegatus and C. v. riverendi. Levels of divergence indicate that large expanses of open sea have not acted as long-term barriers to inter-island dispersal of cyprinodontiform fishes. This study, together with the molecular systematics of other insular Caribbean fishes, indicates that most insular groups originated from late Neogene dispersal from the mainland. The patterns of mtDNA variation in Cyprinodon showed little congruence with the species/subspecies taxonomy.

Animals↗

PubMed2006

A phylogenetic and biogeographic perspective on the evolution of poeciliid fishes.

Phylogenetic relationships of members of the subfamily Poeciliinae (Cyprinodontiformes) are investigated to test alternate hypotheses of diversification resulting from the assembly of the Central America and the Caribbean from the Cretaceous period onwards. We use 4333 aligned base pairs of mitochondrial DNA and 1549 aligned base pairs of nuclear DNA from 55 samples representing 48 ingroup and seven outgroup species to test this hypothesis. Mitochondrial genes analyzed include those encoding the 12S and 16S ribosomal RNAs; transfer RNAs coding for valine, leucine, isoleucine, glutamine, methionine, tryptophan, alanine, asparagine, cysteine and tyrosine; and complete cytochrome b and NADH dehydrogenase subunit I and II; nuclear gene analyzed included the third exon of the recombination activation gene 1 (RAG1). Analyses of combined mtDNA and nuclear DNA data sets result in a well-supported phylogenetic hypothesis. This hypothesis is in conflict with the classical taxonomic assignment of genera into tribes and phylogenetic hypotheses based on the taxonomy; however, the molecular hypothesis defines nine clades that are geographically restricted and consistent with the geological evolution of Central America and the Caribbean. Our analyses support multiple colonization events of Middle America followed by a mix of vicariance and dispersal events.

Animals↗

PubMed2003

Immunocytochemical applications of specific antisera raised against synthetic fragment peptides of mummichog GtH subunits: examining seasonal variations of gonadotrophs (FSH cells and LH cells) in the mummichog and applications to other acanthopterygian fishes.

Two distinct types of gonadotrophs, FSH (GtH I) cells and LH (GtH II) cells, were immunocytochemically identified from mummichog (Fundulus heteroclitus; Cyprinodontiformes, Acanthopterygii) pituitary using antisera raised against synthetic fragment peptides of FSHbeta and LHbeta. Both cell types were abundant during the spawning period (spring and early summer) and decreased in number during the post-spawning immature period. The number of FSH cells increased again during the early phases of gonadal development (cortical alveoli accumulation in the oocytes and basal spermatogenesis) in early winter, whereas the number of LH cells did not. Only FSH cells were abundant during the latter phases of gonadal development (vitellogenesis and active spermatogenesis) in early spring. These observations suggest that both GtHs have important yet different roles for reproduction in this species. Antisera against the conservative region of the FSHbeta and the LHbeta subunits immunostained FSH cells and LH cells, respectively, also in red seabream (Pagrus major; Perciformes, Acanthopterygii) and small mouth bass (Micropterus dolomieu; Perciformes, Acanthopterygii), suggesting the possibility of their use for other acanthopterygian fishes.

Animals↗

PubMed1998

Optomotor response of Anableps anableps depends on the field of view.

Anableps anableps (Cyprinodontiformes) inhabits the niche at the water surface such that its cornea is bisected by the water surface. Consequently, its visual field encompasses simultaneous views into air and water by ventral and dorsal retina, respectively. The optomotor response (OPM) of Anableps was elicited by a moving stimulus pattern in either one or the other environment. Using four related visual displays, we found that this fish exhibits a classical OPM response when presented with suprathreshold flow-fields in its aerial visual field. It lacks an OPM response to the same flow-field when presented in its aquatic visual field, although it may respond by exhibiting optokinetic nystagmus (OKN) and non-OPM motor activity. We conclude that the neurological circuit for the teleost OPM in Anableps operates only for the aerial view and is probably connected to only the ventral retina.

Air↗

PubMed2002

Effects of nonylphenol on the gonadal differentiation of the hermaphroditic fish, Rivulus marmoratus.

Nonylphenol (NP) is an estrogenic degradation product of alkylphenol polyethoxylate surfactants. In this study, the effects of NP on gonadal differentiation and development in Rivulus marmoratus (Osteichthyes, Cyprinodontiformes), a self-fertilizing, hermaphroditic species, were examined. Starting at hatching, fish were exposed to 150 or 300 microg 1(-1) NP (nominal concentrations) in a static system with daily renewal. The measured concentration of NP in the test water decreased rapidly; half-life was 8.0 h. After 60 d of exposure to NP, fish were kept in uncontaminated water for 20 d and were then preserved for histological examination. No fish exposed to 300 microg l(-1) NP (N=8) and only two of nine fish exposed to 150 microg l(-1) NP developed testicular tissue, compared with nine of 13 water-control fish and five of nine solvent-control fish. Oogenesis was also significantly inhibited by NP. None of the fish exposed to 300 microg l(-1) and only two of nine fish exposed to 150 microg l(-1) NP had vitellogenic oocytes, compared with seven of 11 water-control fish (not including males) and six of nine solvent-control fish. Dysplasia of the gonadal lumen also occurred in fish exposed to 300 microg l(-1) NP. These changes, including testicular agenesis, have not been previously reported in fish exposed to NP.

Animals↗

PubMed2001

Chromosome evolution in the annual killifish genus Cynolebias and mitochondrial phylogenetic analysis.

Extensive chromosome variation involving Robertsonian and non-Robertsonian changes were proposed to explain chromosomal evolution within killifishes of the aplocheiloid group belonging to the order Cyprinodontiforms. In the present work we describe the karyotypes of four Cynolebias species and analyze chromosome changes by means of mitochondrial phylogenetic studies, including 10 taxa of this genus. Diploid numbers varied from 48 to 44 and the number of chromosome arms from 50 to 54. Molecular phylogenetic analyses allow us to corroborate previous hypothesis about chromosome evolution in aplocheiloid fishes. The tree topology based on a combined dataset of mitochondrial cytochrome b and 12S genes shows that recent cladogenetic events within the genus Cynolebias could have occurred by allopatric or 'in-situ' differentiation involving chromosomal rearrangements. Our analyses of approximately 10% of mitochondrial genome can be helpful in determining these recent cladogenetic events but it showed limited phylogenetic resolution at intermediate levels of divergence. This can be explained in part by the high levels of DNA sequence divergence (ranging from 0.015 to 0.245) detected at intrageneric level. Different methodological approaches suggest that chromosomal changes in Cynolebias have occurred during their differentiation, supporting the hypothesis that the unresolved basal polytomy could be the result of rapid speciation events, like a true 'star polytomy'.

Animals↗

PubMed2002

Persistence of Mhc heterozygosity in homozygous clonal killifish, Rivulus marmoratus: implications for the origin of hermaphroditism.

The mangrove killifish Rivulus marmoratus, a neotropical fish in the order Cyprinodontiformes, is the only known obligatorily selfing, synchronous hermaphroditic vertebrate. To shed light on its population structure and the origin of hermaphroditism, major histocompatibility complex (Mhc) class I genes of the killifish from seven different localities in Florida, Belize, and the Bahamas were cloned and sequenced. Thirteen loci and their alleles were identified and classified into eight groups. The loci apparently arose approximately 20 million years ago (MYA) by gene duplications from a single common progenitor in the ancestors of R. marmoratus and its closest relatives. Distinct loci were found to be restricted to different populations and different individuals in the same population. Up to 44% of the fish were heterozygotes at Mhc loci, as compared to near homozygosity at non-Mhc loci. Large genetic distances between some of the Mhc alleles revealed the presence of ancestral allelic lineages. Computer simulation designed to explain these findings indicated that selfing is incomplete in R. marmoratus populations, that Mhc allelic lineages must have diverged before the onset of selfing, and that the hermaphroditism arose in a population containing multiple ancestral Mhc lineages. A model is proposed in which hermaphroditism arose stage-wise by mutations, each of which spread through the entire population and was fixed independently in the emerging clones.

Alleles↗

PubMed2026

Parental senescence effects in a short-lived fish.

Senescence is age-related decline that may carry over to subsequent generations. Advanced parental age can both improve or reduce offspring fitness, however. Identification of mechanisms of parental effects senescence thus proved challenging so far. We investigated the effects of old parental age on offspring performance in a laboratory short-lived fish, Nothobranchius furzeri (Cyprinodontiformes). We followed age-related changes in parents and then focused on the effect of parental age on key offspring life-history traits (embryonic survival, hatching rate and juvenile growth). We employed telomere length as a senescence marker and a potential route for transmitting senescence effects from parents to the offspring. As parents aged, their body condition, reproductive output, and telomere length declined. Offspring of older parents showed lower survival and hatching rate. In contrast, old parental age did not compromise juvenile growth and telomere length of the successfully hatched offspring. This, among other things, resulted in decoupling of parent-offspring telomere length. Our study highlights the sensitivity of the early life-stages to old parental age in contrast to offspring post-hatching performance.

Nothobranchius↗

PubMed2000

Spinitectus mexicanus n. sp. (Nematoda : Cystidicolidae) from the intestine of the freshwater fish Heterandria bimaculata in Mexico.

A new nematode, Spinitectus mexicanus n. sp., is described on the basis of the specimens recovered from the intestine of Heterandria bimaculata (Heckel) (Poeciliidae, Cyprinodontiformes) from 3 rivers of the Papaloapan River basin (type locality La Basura River), Los Tuxtlas, Veracruz State, Mexico. It differs from its congeners mainly in having the spination of the cuticle separated into 4 longitudinal sectors, each with posteriorly diminishing numbers of larger spines at the anterior part of body. It is the first species of Spinitectus described from a poeciliid fish and the second reported from freshwater fishes in Mexico.

Animals↗

PubMed2001

Two new species of rhabdochonids (Nematoda: Rhabdochonidae) from freshwater fishes in Mexico, with a description of a new genus.

Two new nematode species, Beaninema nayaritense n. gen., n. sp. and Rhabdochona xiphophori n. sp., are described on the basis of the specimens recovered from the gall bladder and intestine of 2 fishes, Cichlasoma beani (Jordan) (Cichlidae, Perciformes) and Xiphophorus sp. (Poeciliidae, Cyprinodontiformes), respectively, from Mexico. The monotypic genus Beaninema differs from other rhabdochonid genera mainly in the presence of large conical teeth in the middle of the prostom. Rhabdochona xiphophori is characterized mainly by a unique structure of the prostom (presence of 6 anterior teeth; dorsal and ventral teeth unusually broad, with 2 lateral horns) and the shape of the deirids (bifurcated, with markedly long base).

Animals↗

PubMedDate not supplied

The fish fauna in tropical rivers: the case of the Sorocaba River basin, São Paulo, Brazil.

A survey was carried out on the fish species in the Sorocaba River basin, the main tributary of the left margin of the Tietê River, located in the State of São Paulo, Brazil. The species were collected with gill nets. After identification of the specimens, their relative abundance, weight and standard length were determined. Up to the present moment there are not any studies that focus this subject in this hydrographic basin. Fifty-three species, distributed in eighteen families and six orders were collected. Characiformes were represented by twenty-eight species, Siluriformes by seventeen species, the Gymnotiformes by three species, Perciformes and Cyprinodontiformes by two species, and the Synbranchiformes by one species. Among the collected species there were two exotic. The most abundant species were Astyanax fasciatus and Hypostomus ancistroides. In relation to total weight the most representative species were Hoplias malabaricus and Hypostomus ancistroides. Cyprinus carpio, Prochilodus lineatus, Schizodon nasutus and Hoplias malabaricus were the most representative species in relation to average weight. Largest standard length were recorded for Sternopygus macrurus, Steindachnerina insculpta, Eigenmannia aff. virescens and Cyprinus carpio.

Animals↗

PubMed2000

Environmental regulation of annual reproductive cycle in the mosquitofish, Gambusia affinis.

To clarify the environmental factors regulating the annual reproductive cycle of the female mosquitofish, Gambusia affinis, a viviparous teleost, histological changes of the ovary in natural population, and laboratory experiments were examined. The results, extending over two years, suggested that ovarian recrudescence is initiated by the rise in temperature during spring and that ovarian regression is caused by the shorter daylength during late summer. The first rearing experiments using four photoperiod-temperature groups to investigate the factors triggering the onset of reproduction revealed that females with regressing ovaries began reproduction with the rise of temperature regardless of the photoperiod during spring. The results of the second experiment using three different temperature groups indicated that vitellogenesis occurred at over 14 degrees C and pregnancy at over 18 degrees C. The third experiment with four photoperiod-temperature groups was arranged to investigate the factors in the cessation of reproduction. Sexually active females ceased vitellogenesis of the next clutch of oocytes due to the shorter daylength regardless of temperatures during late summer; however, temperature seemed to influence the rate of embryo development. The critical photoperiod is estimated at about 12.5 hr. In nature, it is supposed that vitellogenesis starts when the temperature rises to about 14 degrees C, and final maturation of oocytes occurs when the temperature reaches about 18 degrees C during spring. Then, vitellogenesis of the next clutch of oocytes ceases when the daylength becomes shorter than 12.5 hr during late summer; the last gestation proceeds at a rate dependent on the temperature, and finally reproduction ends by the last parturition. J. Exp. Zool. 286:204-211, 2000.

Animals↗

PubMed1998

Receptor tyrosine kinase Xmrk mediates proliferation in Xiphophorus melanoma cells.

Over-expression of the oncogenic receptor tyrosine kinase (RTK) Xmrk is sufficient to induce formation of hereditary malignant melanoma in the fish Xiphophorus. In the melanoma tissue as well as in a melanoma-derived cell line (PSM), the Xmrk protein shows strong tyrosine phosphorylation, indicating either ligand-independent or autocrine activation of its kinase domain. However, it is unknown whether the constitutively activated Xmrk receptor itself directly triggers the proliferative signals, thus leading to uncontrolled growth of the pigment cells. In order to evaluate the role of Xmrk in proliferation of melanoma cells, we inhibited its kinase activity by using a Xmrk specific tyrphostin. At a concentration of 10 microM, tyrphostin AG555 led to a decrease of the Xmrk-induced DNA synthesis to 10% in NIH 3T3 Hm cells, whereas serum dependent 3H-thymidine incorporation was unaffected. In fish melanoma cells, the drug efficiently blocked DNA synthesis and cellular growth. This anti-proliferative activity correlated with the potency of AG555 to inhibit Xmrk autophosphorylation, indicating that the Xmrk receptor is the major determinant of mitogenic signaling in Xiphophorus melanoma cells.

3T3 Cells↗

PubMed1999

Morphological analysis of the pharyngeal jaws in two populations of Lebias fasciata Valenciennes, 1821 (Teleostei: Cyprinodontidae).

The study of the pharyngeal jaws in two geographically isolated Italian populations of Lebias fasciata indicated the presence of two phenotypes: the Adriatic phenotype with a large ceratobranchial V and upper and lower pharyngeal jaws bearing few large teeth and the Sicilian phenotype with a smaller ceratobranchial V and pharyngeal jaws with smaller and more numerous teeth. The morphological variations of pharyngeal jaws should be interpreted as a result of the geographical isolation of these two populations.

Animals↗

PubMed1998

Mapping of tyrosine kinase gene family members in a Xiphophorus melanoma model.

Xiphophorus fish have been the subject of intensive genetic research for more than 60 yr, primarily because of the availability of a number of interspecific hybrids that are malignant melanoma models with apparently simple oncogene and tumor suppressor gene determinants. The gene map of Xiphophorus is one of the most extensive among nonhuman vertebrates, with about 100 genes assigned to at least 20 independently assorting linkage groups (LGs), as well as more than 250 anonymous DNA sequence markers, providing coverage for most of the genome for genetic mapping studies. This characteristic has resulted in the mapping of a tumor suppressor locus, DIFF, which is one of two genetic determinants of melanoma formation in the best-studied hybrid melanoma, the Gordon-Kosswig melanoma model. The other gene responsible for melanoma formation in this model is a sex-linked tyrosine kinase gene related to EGFR and called Xiphophorus melanoma receptor kinase (Xmrk). The cellular oncogene homologues of the non-receptor tyrosine kinase family orthologous toyes and fyn have also been found to be overexpressed in malignant melanomas of Xiphophorus and may be involved in tumor progression. We report here the map location of a Xiphophorus yes gene, YES1, in LG VI, closest to the EGFR gene and the assignment of a fyn gene homologue to newly designated LG XV, linked to the gene for cytosolic alpha-galactosidase. We also confirmed that an EGFR-related sequence (EGFRL1) that we previously assigned to Xiphophorus LG VI by cross-hybridization to a viral erbB probe was the EGFR orthologue. Our results suggest that the presence of expressed duplicates of members of the tyrosine kinase gene family in teleost fishes may increase the potential number of targets in oncogenic cascades in fish tumor models.

Amino Acid Sequence↗

PubMed2000

Ultrastructural observations on sperm storage in the ovary of the platyfish, Xiphophorus maculatus (Teleostei: poeciliidae): the role of the duct epithelium.

Sperm storage is an important phenomenon occurring in viviparous and oviparous teleosts and contributes to the reproductive life history of these forms. There is a paucity of morphological studies on sperm storage in fishes. The majority of these have been confined to the light level of investigation. In this report, we describe, at the ultrastructural level, sperm storage in the viviparous platyfish, Xiphophorus maculatus. Female platyfish, as is typical of the poeciliids, are capable of storing viable sperm for up to several months within the ovary and gonoduct. We observed that sperm stored within inseminated platyfish became associated with specific epithelial cells (SACs) lining the oviduct. Two forms of association were seen: 1) sperm were found within deep surface pits and pockets, and 2) the spermatozoa were taken up and incorporated within the cytoplasm of the SACs. Junctional complexes in the form of tight junctions (zona occludens) and desmosomes at the apico-lateral surfaces of the SACs were prevalent. The junctions could have contributed to allograft survival of the haploid heterogenetic sperm cells within the female's reproductive tract. Our results shed light on the mechanism of sperm storage in the platyfish and could serve as a model for other poeciliid species and teleosts that are capable of storing sperm.

Animals↗

PubMed1989

Suppression of genetic melanoma in the fish Xiphophorus.

Hybrids between certain species of the teleost Xiphophorus predictably develop melanomas. Classical Mendelian crossing experiments have allowed us to identify genetic loci involved in eliciting and in suppressing tumorigenesis. The overall picture is that melanoma formation results from functional elimination of a suppressor locus allowing abnormal expression of a melanoma locus. Melanoma formation in Xiphophorus behaves like a recessive trait. The fish melanomas consist of incompletely differentiated pigment cells and in many aspects resemble their murine and human counterparts. Cytogenetic studies of cells of the genetic melanomas have provided evidence for chromosomal abnormalities. In particular, cytogenetic manifestations of amplified DNA were detected in a cell line derived from a malignant melanoma. Amplified DNA was isolated and was found to be amplified in a particular type of genetic melanoma. Our results suggest that genetic changes in addition to elimination of suppressor genes contribute to the malignant phenotype of melanoma in Xiphophorus. It is possible that a similar situation occurs in cancers of higher vertebrates, including humans.

Animals↗