Paulo Roberto Antunes de Mello Affonso

Assessing genetic diversity of Brazilian reef fishes by chromosomal and DNA markers.

Little is known on genetics of Brazilian coral reef fish and most of this information is limited to chromosome characterization of major representative species. The diploid chromosome number in marine fish varies from 2n= 22–26 to 2n = 240–260. Despite of this apparent diversity, most studied marine species have a diploid complement with 48 acrocentric chromosomes. This latter trend is mostly observed among Perciformes, an important major taxon of coral reef fishes. Studies in the families Pomacentridae, Pomacanthidae and Chaetodontidae, for example, have shown a common karyotype pattern entirely formed by 48 uniarmed chromosomes. However, rare numerical and structural chromosome polymorphisms and cryptic chromosome rearrangements involving heterochromatin segments and/or nucleolar organizing sites have been reported among such fishes. Although new chromosome forms can contribute to the establishment of genetically isolated populations, their role in reef fish speciation at marine realm still is an open question. More recently, genomic DNA analyses using RAPD and microsatellites, and sequencing and RFLP of mitochondrial DNA have increasingly been used in Atlantic reef fish species. Genetic homogeneity over wide geographical ranges has been reported for different fish groups, in contrast to several cases of population substructuring related to environmental constraints or evolutionary history. Amazonas outflow and upwelling on the Southeastern coast of Brazil are believed to be strong barriers to dispersal of some reef species. Moreover, it is suggested that the pattern of speciation and population structure at South Atlantic is quite distinctive from Pacific Ocean, even when comparing closely related taxa. Further genetic studies are strongly encouraged in Brazilian reef fishes in order to provide a reliable scenario of the genetic structure in this important and diverse fish group.

Chromosomal diversification of reef fishes from genus Centropyge (Perciformes, Pomacanthidae).

The genus Centropyge is remarkable for species richness, composing a highly specialized fish group amongst members from family Pomacanthidae. However, cytogenetical reports are nearly absent in these animals. New data are provided from karyotypical studies carried out on Centropygeaurantonotus from the Brazilian coast of the Atlantic Ocean and C. ferrugatus from the Philippines Sea of the Indo-Pacific Ocean. Both species present 2n=48 but karyotypes are differentiated by fundamental number. C. aurantonotus has a great number of biarmed chromosomes (4xa0mxa0+xa014xa0sm+16xa0st+4xa0a), while C. ferrugatus presents only acrocentric chromosomes. Single nucleolar organizer regions (NORs) are located at interstitial position of an acrocentric pair in C. ferrugatus and on short arms of a subtelocentric pair in C. aurantonotus, as confirmed by fluorescent in situ hybridization (FISH) with 18S rDNA probes. Heterochromatin is distributed over NOR and centromeric regions in both species, but additional GC-rich heterochromatic blocks on short arms of up to eight chromosomal pairs can be detected in C. aurantonotus. 5S rDNA segments were located interstitially on two chromosomal pairs in C. ferrugatus and on nine pairs in C. aurantonotus, mostly equivalent to heterochromatic blocks on short arms of biarmed chromosomes. C. ferrugatus can be considered a species in which basal chromosomal features proposed for modern Teleosteans were conserved. The derived karyotype pattern of C. aurantonotus seems to be determined by pericentric inversions and heterochromatin addition which probably determined the notorious dispersion of 5S rRNA (pseudo)genes. It is demonstrated that, even within a group generally characterized by cytogenetical homogeneity as the family Pomacanthidae, diversified karyotypes can be found.

Close karyotypical relationship between two species of marine angelfishes from South Atlantic: Pomacanthus arcuatus and P. paru (Perciformes, Pomacanthidae)

Abstract Several cytogenetical studies on marine Perciformes have demonstrated a conservative chromosomal pattern. Despite of some exceptions, even more specialized groups such as those from coral reefs have followed this trend. Nevertheless, the number of karyotypical information on fish from this environment is relatively reduced. In this work, cytogenetical data were obtained from two species of family Pomacanthidae (Perciformes), widespread throughout the Brazilian coast and associated to reefs: Pomacanthus paru and P. arcuatus. Both species have the same chromosomal constitution. The respective karyotypes are composed by one subtelocentric pair and 23 acrocentric pairs (2n=48). Single NORs are located on short arms of the subtelocentric pair. Heterochromatic blocks are restricted to centromeres and NORs. An accentuated NOR size heteromorphism between homologous was detected and analyses by chromomycin A3 demonstrated that it can be attributed to structural chromosome differences. A model of NOR evolution in Pomacanthus is proposed by pericentric inversion. Finally, the high level of resemblance between karyotypes from both species indicates their close phylogenetic relationship and diverges, although slightly, from the cytogenetical pattern so far described for Pomacanthidae representatives.

A Unique Sex Chromosome System in the Knifefish Gymnotus bahianus with Inferences About Chromosomal Evolution of Gymnotidae

Cytogenetic studies in Neotropical electric knifefish of genus Gymnotus have shown a remarkable interspecific variability, including distinct sex chromosome systems. In this study, we present the first chromosomal data in Gymnotus bahianus from Contas River basin, northeastern South America. Based on extensive analyses, the modal diploid values were 2n = 36 (30m/sm + 6st) for females and 2n = 37 (32m/sm + 5st) for males. Therefore, a novel XX/XY1Y2 sex chromosome system is described for the genus. Single nucleolar organizer regions (NORs) interspersed to GC-rich sites were detected on a subtelocentric pair (7th) for both sexes and confirmed by fluorescent in situ hybridization with 18S rDNA probes. Heterochromatin was detected at pericentromeric regions of all chromosomes and interspersed to NORs on pair 7 and 5S rDNA cistrons on pair 9. The highly differentiated karyotype of Gymnoytus bahianus, with low diploid numbers and a unique XX/XY1Y2 system, reinforces the independent origin of sex chromosomes in Gymnotiformes and seems to reflect the particular evolutionary history of this species in a small and isolated drainage system. Moreover, in spite of morphological similarities, the present results indicate a remarkable chromosomal divergence in relation to closely related species such as G. sylvius and G. carapo.

Revealing Hidden Diversity of the Underestimated Neotropical Ichthyofauna: DNA Barcoding in the Recently Described Genus Megaleporinus (Characiformes: Anostomidae)

Molecular studies have improved our knowledge on the neotropical ichthyofauna. DNA barcoding has successfully been used in fish species identification and in detecting cryptic diversity. Megaleporinus (Anostomidae) is a recently described freshwater fish genus within which taxonomic uncertainties remain. Here we assessed all nominal species of this genus using a DNA barcode approach (Cytochrome Oxidase subunit I) with a broad sampling to generate a reference library, characterize new molecular lineages, and test the hypothesis that some of the nominal species represent species complexes. The analyses identified 16 (ABGD and BIN) to 18 (ABGD, GMYC, and PTP) different molecular operational taxonomic units (MOTUs) within the 10 studied nominal species, indicating cryptic biodiversity and potential candidate species. Only Megaleporinus brinco, Megaleporinus garmani, and Megaleporinus elongatus showed correspondence between nominal species and MOTUs. Within six nominal species, a subdivision in two MOTUs was found, while Megaleporinus obtusidens was divided in three MOTUs, suggesting that DNA barcode is a very useful approach to identify the molecular lineages of Megaleporinus, even in the case of recent divergence (< 0.5 Ma). Our results thus provided molecular findings that can be used along with morphological traits to better define each species, including candidate new species. This is the most complete analysis of DNA barcode in this recently described genus, and considering its economic value, a precise species identification is quite desirable and fundamental for conservation of the whole biodiversity of this fish.

Sequential Steps of Chromosomal Differentiation in Atlantic Surgeonfishes: Evolutionary Inferences

Surgeonfishes are a species-rich group and a major biomass on coral reefs. Three species are commonly found throughout South Atlantic, Acanthurus bahianus, A. chirurgus, and A. coeruleus. In this paper, we present the first cytogenetic data of these species, revealing a sequential chromosomal diversification. A. coeruleus was characterized by a relatively conserved karyotype evolved by pericentric inversions of some pairs (2n = 48, 2sm + 4st + 42a). In contrast, the karyotypes of A. bahianus (2n = 36) and A. chirurgus (2n = 34) were highly differentiated by the presence of six large metacentric pairs in A. bahianus (12m + 2sm + 4st + 18a) and A. chirurgus (12m + 2sm + 4st +1 6a) probably derived by chromosomal fusions that corroborate their closer relationship. A discernible in tandem fusion represents an autapomorphic character to A. chirurgus. In spite of macrostructure variation, single nucleolar organizer regions (NORs) on short arms of a subtelocentric pair and similar distribution of C-bands were observed in the three species. Overlapping of chromosomal data with molecular phylogeny indicated pericentric inversions which took place nearly at 19u2009Ma while centric fusions are as recent as 5u2009Ma. A physical mapping of coding and noncoding sequences in Acanthurus could clarify the role of additional rearrangements during their chromosomal evolution.

First Report of Sex Chromosomes in Achiridae (Teleostei: Pleuronectiformes) with Inferences About the Origin of the Multiple X1X1X2X2/X1X2Y System and Dispersal of Ribosomal Genes in Achirus achirus.

American soles (family Achiridae) have been characterized by remarkable chromosomal variation even though several species lack basic cytogenetic information. This trend indicates that chromosomal traits can be useful to taxonomy once the morphological identification of some taxa in this family (e.g., Achirus species) is controversial. In this work, we expand the cytogenetic data in Achiridae by providing the first karyotypic analysis of Achirus achirus. An unusual multiple sex chromosome system (X1X1X2X2/X1X2Y) was detected, once males presented 2nu2009=u200933 with three unpaired chromosomes (X1X2Y) while females presented 2nu2009=u200934 with two acrocentric pairs (X1X1 and X2X2) found in hemizygosis in males. The 18S rDNA clusters were observed interspersed with GC-rich sites in a single pair. However, the 5S rRNA genes were dispersed through the genome of A. achirus in a sex-specific manner (10 clusters in males and 12 in females), as a result of the presence of ribosomal cistrons in X1 and X2 chromosomes. This pattern allowed us to infer that Y chromosome has evolved by partial deletion followed by fusion of proto-X1 and proto-X2 homologous chromosomes. The high rate of genomic evolution in Achiridae could have favored their reproductive isolation and speciation even in sympatric conditions.

Correlações Genéticas entre Características de Crescimento e Parâmetros da Curva em Bovinos da Raça Nelore

Esta pesquisa foi realizada com o objetivo de se estimar os coeficientes de herdabilidades e correlacoes geneticas e fenotipicas entre as caracteristicas P205, P365, P550, D160 e D240 com os parâmetros A (valor assintotico ou peso a maturidade) e k (taxa de maturacao) da curva de crescimento. Utilizaram-se dados de 3.061 animais, pesados trimestralmente, do nascimento aos dois anos de idade. As estimativas dos parâmetros da curva foram analisadas por meio da tecnica dos modelos nao-lineares, utilizando o modelo logistico e o metodo de Gauss Newton. Para obter as estimativas dos componentes de (co)variâncias, empregou-se a metodologia da Maxima Verossimilhanca Restrita Livre de Derivada (DFREML), por meio de modelos animais bi-caracteristica. As herdabilidades foram 0,15; 0,08; 0,27; 0,34; 0,31; 0,28 e 0,25, para A, k, P205, P365, P550, D160 e D240, respectivamente. As correlacoes geneticas do parâmetro A com as outras caracteristicas foram: -0,67 (k), 0,68 (P205), 0,68 (P365), 0,75 (P550), -0,45 (D160) e -0,42 (D240). As correlacoes geneticas do parâmetro k foram 0,14 (P205), 0,30 (P365), 0,24 (P550), -0,43 (D160) e 0,13 (D240). Os resultados obtidos sugerem que a selecao para P205, P365 e P550 resulta em aumento no peso a maturidade. Por outro lado, as caracteristicas D160 e D240 proporcionam menor ganho indireto no parâmetro A, devido a menor magnitude da associacao genetica. A selecao baseada em D160 ocasiona progresso genetico favoravel na taxa de maturacao.

ZZ/ZW sex chromosome system in the endangered fish Lignobrycon myersi Miranda-Ribeiro, 1956 (Teleostei, Characiformes, Triportheidae).

Abstract Lignobrycon myersi is an endemic fish species from a few coastal rivers in northeastern Brazil. Based on molecular evidence, Lignobrycon myersi and genera Triportheus Cope, 1872, Agoniates Müller & Troschel, 1845, Clupeacharax Pearson, 1924 and Engraulisoma Castro, 1981 were placed in the family Triportheidae. In the present work, we report the first cytogenetic data for Lignobrycon myersi to test the hypothesis that Lignobrycon and Triportheus are closely related. Studied specimens presented 2n=52 with 28 metacentric (m), 18 submetacentric (sm) and six subtelocentric (st) chromosomes for males and 27 m, 19 sm and 6 st for females, characterizing a ZZ/ZW sex chromosome system. The Z chromosome corresponds to the largest chromosome in karyotype while the W is about 50% smaller than the Z and largely heterochromatic. Terminal nucleolus organizer regions, GC-rich sites and 18S rDNA signals were detected on pair 14. However, additional 18S rDNA sites were observed in the W chromosome. The 5S rDNA was mainly detected on long arms of pair 7. The apparent synapomorphic chromosomal traits of Triportheus and Lignobrycon myersi reinforce their close phylogenetic relationship, suggesting that the ZZ/ZW chromosome system in both genera has arisen before cladogenic events.

Chromosomal Evolution and Cytotaxonomy in Wrasses (Perciformes; Labridae)

The wrasses (family Labridae) represent a suitable model to understand chromosomal evolution and to test the efficacy of cytotaxonomy since they display a remarkable karyotypic variation, rarely reported in marine Perciformes, as well as a high number of species and complex systematics. Therefore, we provided new chromosomal data in 5 labrids from South Atlantic (Doratonotus megalepis, Halichoeres dimidiatus, Halichoeres penrosei, Thalassoma noronhanum, and Xyrichtys novacula) and carried out a detailed comparative analysis of karyotypic data in Labridae using multivariate approaches. Basal diploid values (2n = 48) were observed in most of species studied in the present work but D. megalepis (2n = 46), along with distinct karyotype formulae. Single 18S rDNA sites interspersed with GC-rich heterochromatin were also commonly reported except for both Halichoeres species (2 18S rDNA-bearing pairs), following a species-specific pattern. These data show the high rates of chromosomal evolution in wrasses, ranging from microstructural rearrangements to centric fusions. A revision of chromosomal data in Labridae based on multivariate analysis of 74 taxa allowed inferring karyoevolutionary trends within tribes and genera of wrasses. The dendrogram obtained was in agreement with recent systematic hypotheses. In spite of the independent occurrence of some chromosomal rearrangements, karyoevolutionary trends could be identified within tribes of Labridae. Moreover, the karyotypic features are also suitable as cytotaxonomic markers of wrasses.