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      Astyanax hastatus Myers, 1928 (Teleostei, Characidae): a new species complex within the genus Astyanax?

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          Abstract

          Four populations of Astyanax hastatus Myers 1928 from the Guapimirim River basin (Rio de Janeiro State) were analyzed and three distinct cytotypes identified. These cytotypes presented 2n = 50 chromosomes, with 4M+8SM+10ST+28A (Cytotype A), 8M+10SM+14ST+18A (Cytotype B), 6M+8SM+4ST+32A (Cytotype C) and scanty heterochromatin, mainly located throughout pericentromeric regions of several chromosomal pairs. No homologies with the As-51 satellite DNA were observed in the three cytotypes, although all of them presented multiple 18S rDNA sites, as detected by both silver nitrate staining and FISH (fluorescent in situ hybridization). The application of the term "species complex" in Astyanax is discussed from a cytotaxonomic viewpoint.

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          A species definition for the modern synthesis.

          James Mallet (1995)
          One hundred and thirty-six years since On the Origin of Species 3., biologists might be expected to have an accepted theory of speciation. Instead, there is, if anything, more disagreement about speciation than ever before. Even more surprisingly, 60 years after the biological species concept, in which species were considered to be reproductive communities isolated from other such communities, we still do not all accept a common definition of what a species is. And yet, if speciation is to be any different from ordinary evolution, we must have a clear definition of species. The emerging solution to the species problem is an updated, genetic version of Darwin's own definition. This definition is useful and is already being used in taxonomy, in biodiversity studies and in evolution.
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            Cavefish as a model system in evolutionary developmental biology.

            William Jeffery (2001)
            The Mexican tetra Astyanax mexicanus has many of the favorable attributes that have made the zebrafish a model system in developmental biology. The existence of eyed surface (surface fish) and blind cave (cavefish) dwelling forms in Astyanax also provides an attractive system for studying the evolution of developmental mechanisms. The polarity of evolutionary changes and the environmental conditions leading to the cavefish phenotype are known with certainty, and several different cavefish populations have evolved constructive and regressive changes independently. The constructive changes include enhancement of the feeding apparatus (jaws, taste buds, and teeth) and the mechanosensory system of cranial neuromasts. The homeobox gene Prox 1, which is expressed in the expanded taste buds and cranial neuromasts, is one of the genes involved in the constructive changes in sensory organ development. The regressive changes include loss of pigmentation and eye degeneration. Although adult cavefish lack functional eyes, small eye primordia are formed during embryogenesis, which later arrest in development, degenerate, and sink into the orbit. Apoptosis and lens signaling to other eye parts, such as the cornea, iris, and retina, result in the arrest of eye development and ultimate optic degeneration. Accordingly, an eye with restored cornea, iris, and retinal photoreceptor cells is formed when a surface fish lens is transplanted into a cavefish optic cup, indicating that cavefish optic tissues have conserved the ability to respond to lens signaling. Genetic analysis indicates that multiple genes regulate eye degeneration, and molecular studies suggest that Pax6 may be one of the genes controlling cavefish eye degeneration. Further studies of the Astyanax system will contribute to our understanding of the evolution of developmental mechanisms in vertebrates.
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              The American Characidae

              CH Eigenmann, CH Eigenmann, GS MYERS … (1921)
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                Author and article information

                Contributors
                Karine Frehner Kavalco: Role: ND
                Karina de Oliveira Brandão: Role: ND
                Rubens Pazza: Role: ND
                Lurdes Foresti de Almeida-Toledo: Role: ND
                Journal
                Journal ID (publisher): gmb
                Title: Genetics and Molecular Biology
                Abbreviated Title: Genet. Mol. Biol.
                Publisher: Sociedade Brasileira de Genética (Ribeirão Preto )
                ISSN: 1678-4685
                Publication date (Print): 2009
                Volume: 32
                Issue: 3
                Pages: 477-483
                Affiliations
                [1 ] Universidade Federal de Viçosa Brazil
                [2 ] Universidade de São Paulo Brazil
                Article
                Publisher ID: S1415-47572009000300009
                SO-VID: 90e201e9-b470-4675-add5-0c5f63a1b581
                License:

                http://creativecommons.org/licenses/by/4.0/

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                Product

                SciELO Brazil

                Self URI (journal page): http://www.scielo.br/scielo.php?script=sci_serial&pid=1415-4757&lng=en
                Categories
                Subject: BIOCHEMISTRY & MOLECULAR BIOLOGY
                Subject: GENETICS & HEREDITY

                ScienceOpen disciplines: Molecular biology,Genetics
                Keywords: Astyanax hastatus,molecular cytogenetics,karyotypic evolution,species complex
                Data availability:
                ScienceOpen disciplines: Molecular biology, Genetics
                Keywords: Astyanax hastatus, molecular cytogenetics, karyotypic evolution, species complex

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