Resumo
The fish species Synbranchus marmoratus has been reported to exist as a species complex due to high intraspecific karyotypic variability in spite of the difficulty or impossibility to distinguish them using morphological traits alone. The goal of this work was to use cytogenetic and molecular methods to determine the species delimitations and understand the karyoevolution of S. marmoratus using samples collected from distinct Brazilian localities. Among the analyzed specimens, a large degree of cytogenetic variation related to diploid numbers and karyotype structure was observed, with karyotypes showing 2n=42, 44 and 46 chromosomes. In addition, using sequences of three mitochondrial genes, the phylogenetic relationships between every sample with a known karyotype were determined, which revealed significant nucleotide divergence among the karyomorphs. Also, the analyses indicate that chromosomal rearrangements occurred independently within the distinct lineages of S. marmoratus complex, which resulted in the appearance of distinct karyotypic variants in a non-linear fashion related to diploid numbers and in the appearance of similar non-homologous chromosomes. Finally, the integration of both molecular cytogenetic and phylogenetic approaches allowed the determination of specific chromosomes possibly involved in rearrangements and a better understanding about the evolutionary processes involved in the differentiation of Synbranchus genus.(AU)
A espécie de peixe Synbranchus marmoratus tem sido reportada como um complexo de espécies devido à elevada variabilidade cariotípica intraespecífica a despeito da dificuldade ou impossibilidade de distingui-las usando apenas caracteres morfológicos. O objetivo deste trabalho foi utilizar métodos citogenéticos e moleculares para determinar a delimitação das espécies e compreender a carioevolução de S. marmoratus utilizando amostras coletadas em distintas localidades brasileiras. Dentre os espécimes analisados, um alto grau de variação citogenética relativo aos números diploides e estrutura cariotípica foi observado, com cariótipos mostrando 2n=42, 44 e 46 cromossomos. Adicionalmente, utilizando sequências de três genes mitocondriais, as relações filogenéticas entre cada amostra com cariótipo conhecido foram determinadas, revelando uma divergência nucleotídica significativa entre os cariomorfos. Além disso, as análises indicam que rearranjos cromossômicos ocorreram independentemente nas distintas linhagens do complexo S. marmoratus, o que resultou no aparecimento de distintas variantes cariotípicas de forma não linear em relação aos números diploides e no surgimento de cromossomos similares e não homólogos. Finalmente, a integração de uma abordagem citogenética molecular e filogenética permitiu a determinação de cromossomos específicos que, possivelmente, estão envolvidos em rearranjos e um melhor entendimento sobre os processos evolutivos envolvidos na diferenciação do gênero Synbranchus.(AU)
Assuntos
Animais , Filogenia , Transferência Genética Horizontal/genética , Análise Citogenética/veterinária , Peixes/genética , Especificidade da EspécieResumo
Individual samples from five populations of the characid fish Astyanax scabripinnis (Jenyns, 1842) from the Tietê and Paranapanema river basins (Brazil) were studied. All individuals analyzed presented 50 chromosomes but three different karyotypic forms were observed. Additionally, some individuals of one karyomorph presented a macro supernumerary chromosome. No chromosomal differentiation was observed between males and females in any sample analyzed. C-banding revealed two distinct distribution patterns in these populations in which strong terminally located heterochromatic blocks were detected in the long arms of some chromosomes of the specimens from Cascatinha, Cintra, and Funari streams, whereas populations of the Capão Bonito stream and the Barbosa waterfall revealed less evident heterochromatic blocks on the chromosomes. The comparative study of the 18S rDNA localization by fluorescent in situ hybridization, and detection of active nucleolus organizing regions by silver stain (Ag-NORs) showed differences in rDNA content and expression of this gene site among the individuals analyzed. Chromosome mapping of the 5S rDNA revealed the presence of four sites located in two distinct chromosomal pairs, with no apparent differences among karyomorphs. Based on the biogeographical distribution and specific biological characteristics of the species, the data focus on the chromosome differentiation mechanisms involved in the speciation process acting on the populations of the Astyanax scabripinnis species complex.
Resumo
Individual samples from five populations of the characid fish Astyanax scabripinnis (Jenyns, 1842) from the Tietê and Paranapanema river basins (Brazil) were studied. All individuals analyzed presented 50 chromosomes but three different karyotypic forms were observed. Additionally, some individuals of one karyomorph presented a macro supernumerary chromosome. No chromosomal differentiation was observed between males and females in any sample analyzed. C-banding revealed two distinct distribution patterns in these populations in which strong terminally located heterochromatic blocks were detected in the long arms of some chromosomes of the specimens from Cascatinha, Cintra, and Funari streams, whereas populations of the Capão Bonito stream and the Barbosa waterfall revealed less evident heterochromatic blocks on the chromosomes. The comparative study of the 18S rDNA localization by fluorescent in situ hybridization, and detection of active nucleolus organizing regions by silver stain (Ag-NORs) showed differences in rDNA content and expression of this gene site among the individuals analyzed. Chromosome mapping of the 5S rDNA revealed the presence of four sites located in two distinct chromosomal pairs, with no apparent differences among karyomorphs. Based on the biogeographical distribution and specific biological characteristics of the species, the data focus on the chromosome differentiation mechanisms involved in the speciation process acting on the populations of the Astyanax scabripinnis species complex.
Resumo
Individual samples from five populations of the characid fish Astyanax scabripinnis (Jenyns, 1842) from the Tietê and Paranapanema river basins (Brazil) were studied. All individuals analyzed presented 50 chromosomes but three different karyotypic forms were observed. Additionally, some individuals of one karyomorph presented a macro supernumerary chromosome. No chromosomal differentiation was observed between males and females in any sample analyzed. C-banding revealed two distinct distribution patterns in these populations in which strong terminally located heterochromatic blocks were detected in the long arms of some chromosomes of the specimens from Cascatinha, Cintra, and Funari streams, whereas populations of the Capão Bonito stream and the Barbosa waterfall revealed less evident heterochromatic blocks on the chromosomes. The comparative study of the 18S rDNA localization by fluorescent in situ hybridization, and detection of active nucleolus organizing regions by silver stain (Ag-NORs) showed differences in rDNA content and expression of this gene site among the individuals analyzed. Chromosome mapping of the 5S rDNA revealed the presence of four sites located in two distinct chromosomal pairs, with no apparent differences among karyomorphs. Based on the biogeographical distribution and specific biological characteristics of the species, the data focus on the chromosome differentiation mechanisms involved in the speciation process acting on the populations of the Astyanax scabripinnis species complex.
Resumo
Cytogenetic analysis of the Amazon stingless bee Melipona seminigra merrillae, by conventional Giemsa staining and C-banding, revealed a different chromosome number for Melipona: 2n = 22 for females and diploid drones while the haploid drones present n = 11. There is no evidence of B chromosomes. This result contrasts with previous studies, in which the chromosome number of 19 Melipona species was determined as 2n = 18 for females and n = 9 for haploid males. Based on cytogenetic information available for other Melipona species, we propose that M. s. merrillae has a more derived diploid number. This indicates that chromosome number is not a conservative characteristic within the genus as previously thought. Cytogenetic data for stingless bees are scarce, especially in Amazon region. Additional studies will be very important in order to promote Melipona karyoevolution discussion and consequently a taxonomy review.
Resumo
Cytogenetic analysis of the Amazon stingless bee Melipona seminigra merrillae, by conventional Giemsa staining and C-banding, revealed a different chromosome number for Melipona: 2n = 22 for females and diploid drones while the haploid drones present n = 11. There is no evidence of B chromosomes. This result contrasts with previous studies, in which the chromosome number of 19 Melipona species was determined as 2n = 18 for females and n = 9 for haploid males. Based on cytogenetic information available for other Melipona species, we propose that M. s. merrillae has a more derived diploid number. This indicates that chromosome number is not a conservative characteristic within the genus as previously thought. Cytogenetic data for stingless bees are scarce, especially in Amazon region. Additional studies will be very important in order to promote Melipona karyoevolution discussion and consequently a taxonomy review.