Comparative cytogenetics of Carnegiella marthae and Carnegiella strigata (Characiformes, Gasteropelecidae) and description of a ZZ/ZW sex chromosome system

Comparative cytogenetic analyses of hatchetfishes Carnegiella marthae and Carnegiella strigata (Gasteropelecidae) from the Rio Negro basin were performed using conventional Giemsa staining, silver (Ag) -staining and C-banding. The diploid chromosome numbers of both species equaled 2n = 50 but their karyotypes were distinct. We found evidence for sex chromosomes in C. marthae since karyotype of males presented 20 M + 12 SM + 4 ST + 14 A and ZZ ST chromosomes while the females presented 20 M + 12 SM + 4 ST + 14 A and ZW ST chromosomes of distinct size. Conversely, C. strigata presented 4 M + 4 SM + 2 ST + 40 A chromosomes without sex chromosome heteromorphism. Karyotypes of both species had two NOR-bearing SM chromosomes of distinct size indicating the presence of multiple NOR phenotypes. The sex chromosome pair had specific C-banding pattern allowing identification of both Z and W. This heteromorphic system has previously been described for the gasteropelecids.

Cytotaxonomy and karyoevolution of the genus Crenicichla (Perciformes, Cichlidae)

Karyotypes of six cichlid species of the genus Crenicichla were investigated. The species C. cincta, C. inpa, C. reticulata, C. lugubris, and C. cf. johanna were collected from Amazon basin, and C. britskii was collected from the Paraná-Paraguai basin. All of the analysed species showed 2n = 48 chromosomes; however, C. cincta, C. lugubris, C. cf. johanna, and C. britskii had a karyotype formula of 8M-SM+40ST-A, FN = 56, while C. inpa and C. reticulata exhibited the formula 6M-SM+42ST-A, FN = 54. Analysis of active Ag-NORs revealed two NOR-bearing chromosomes in all species; however, theses cistrons were located on different chromosome pairs and/or in different chromosome locations in each species. This condition bears evolutionary significance, since it is the main chromosome marker of the process of karyotypic evolution among the species of the genus Crenicichla. In general, C-banding revealed a similar constitutive heterochromatin pattern in all species, although it was possible to detect some features that led us to infer that Crenicichla also presents a species-specific heterochromatin pattern.

Analysis of toxicity on Bacillus sphaericus from amazonian soils to Anopheles darlingi and Culex quinquefasciatus larvae / Análise da toxicidade em Bacillus sphaericus de solos da Amazônia em larvas de Anopheles darlingi e Culex quinquefasciatus

Bioassays under laboratory conditions aiming to determine the larvicidal activity of Bacillus sphaericus were carried out on Anopheles darlingi and Culex quinquefasciatus. In order to estimate the toxicity through median lethal concentration (LC50) and the relative potency of the strains to B. sphaericus standard strain 2362, probit analysis was performed utilizing the POLO-PC program. The findings of LC50 pointed out high effectiveness on strains IB15 (0.040 ppm), IB19 and S1116 (0.048 ppm), IB16 (0.052 ppm) and S265 (0.057 ppm). Strain IB15 presented nearly 50 percent more potency than strain 2362 in bioassays conducted on A. darlingi. It was observed that IB16 and S1116 strains were the most powerful against C. quinquefasciatus, showing to be about 300-400 percent stronger than 2362 strain. The results show that laboratory conditioned evaluation can be an important way to select promising bacteria with entomopathogenic action on biolarvicides production for use on mosquitoes breeding sites.

Bioensaios sob condições de laboratório foram realizados em larvas de Anopheles darlingi e Culex quinquefasciatus, visando determinar a atividade larvicida de Bacillus sphaericus. Para estimar a toxicidade através da concentração letal mediana (CL50) e a potência das estirpes em relação à estirpe padrão 2362, foi realizada a análise de probit utilizando o programa POLO-PC. Os resultados da CL50 apontaram alta efetividade para as estirpes IB15 (0,040 ppm), IB19 e S1116 (0,048 ppm), IB16 (0,052 ppm) e S265 (0,057 ppm). A estirpe IB15 apresentou potência cerca de 50 por cento maior que a estirpe 2362 nos bioensaios realizados com A. darlingi. Foi observado que as estirpes IB16 e S1116 foram as mais tóxicas para controle de C. quinquefasciatus, mostrando-se cerca de 300-400 por cento mais potente. Os resultados mostram que a avaliação em laboratório é uma importante etapa para selecionar bactérias com ação entomopatogênica a serem usadas na para a produção de biolarvicidas para uso nos criadouros das larvas de mosquitos.

Insertion sequences as variability generators in the Mycoplasma hyopneumoniae and M. synoviae genomes

We have analyzed the sequenced genomes of three strains of Mycoplasma hyopneumoniae and one strain of M. synoviae, and have found three and two different transposable element families, respectively in each species. In M. hyopneumoniae, the Insertion Sequences of the IS4 family is represented by ISMHp1, a putatively active element. The IS3 family is represented by several degenerated sequences. A third element called tMH was found, which shows some characteristics reminiscent of retrotransposons. In M. synoviae, three different possibly active IS4 elements are present (ISMHp1-like; ISMs1 and IS1634-like elements). The IS30 family is represented by the degenerated IS1630-like element. The IS1634-like element is shown to be involved in chromosomal rearrangements and horizontal gene transfer (HGT). The ISMHp1-like element is shown to relate to the HGT of a 25-kb region from M. gallisepticum to M. synoviae. The fractions of these genomes that correspond to mobile elements varied from 1.35 to 3.13 percent in M. hyopneumonia strains and was 2.08 percent in M. synoviae. Although these species possess reduced genomes, they maintain mobile elements, perhaps as a mechanism for genetic variability production.

Esterase-D and chromosome patterns in Central Amazon piranha (Serrasalmus rhombeus Linnaeus, 1766) from Lake Catalão

This study presents additional genetic data on piranha (Serrasalmus rhombeus Linnaeus, 1766) complex previously diagnosed due to the presence of distinct cytotypes 2n = 58 and 2n = 60. Three esterase-D enzyme loci (Est-D1, Est-D2 and Est-D3) were examined and complemented with chromosomal data from 66 piranha specimens collected from Lake Catalão. For all specimens the Est-D1 and Est-D2 loci were monomorphic. In contrast, the Est-D3 locus was polymorphic with genotypes and alleles being differentially distributed in the previously described cytotypes and served as the basis for detecting a new cytotype (2n = 60 B). In cytotype 2n = 58 the Est-D3 locus was also polymorphic and presented Mendelian allelic segregation with four genotypes (Est-D3(11), Est-D3(12), Est-D3(22) and Est-D3(33)) out of six theoretically possible genotypes, presumably encoded by alleles Est-D3¹ (frequency = 0.237), EsT-D3² (0.710) and Est-D3³ (0.053). A Chi-squared (chi2) test for Hardy-Weinberg equilibrium was applied to the Est-D3 locus and revealed a genetic unbalance in cytotype 2n = 58, indicating the probable existence in the surveyed area of different stocks for that karyotypic structure. A silent null allele (Est-D3(0)) with a high frequency (0.959) occurred exclusively in the 2n = 60 cytotype. On the other hand, the new cytotype 2n = 60 B described here for the first time was monomorphic for the presumably fixed Est-D3³ allele. The data as a whole should contribute to the better understanding the rhombeus complex taxonomic status definition in the Central Amazon.

Cytogenetic studies of two freshwater sciaenids of the genus Plagioscion (perciformes, sciaenidae) from the Central Amazon

Foram estudados, pela primeira vez, os cariótipos de duas espécies de sciaenídeos de água doce, pertencentes ao gênero Plagioscion (P. squamosissimus e Plagioscion sp.), através de técnicas de coloraçäo convencional (Giemsa), NOR e banda C. Todos os indivíduos apresentaram 2n=48, NOR simples e banda C preferencialmente pericentromérica. Porém, a fórmula cariotípica e a localizaçäo das NORs permitiram-nos evidenciar diferenças inter- e intra-específicas. Em P. squamosissimus, as NORs estäo localizadas em posiçäo proximal nos braços longos do último par do complemento e säo heteromórficas em relaçäo ao tamanho das marcaçöes. Aparentemente, esse heteromorfismo de NOR está associado com diferenças populacionais. Por outro lado, Plagioscion sp. apresentou dois citótipos. O citótipo a é caracterizado por 2 cromossomos metacêntricos e 46 acrocêntricos, enquanto o citótipo b é caracterizado por 48 cromossomos acrocêntricos. Em ambos citótipos, as NORs estäo localizadas em posiçäo proximal nos braços longos do primeiro par de cromossomos do complemento. Porém, no citótipo a essas marcaçöes localizam-se em um par de cromossomos metacêntricos, enquanto no citótipo b em um acrocêntrico.