Sandra Mariotto

Chromosomal diversification in ribosomal DNA sites in Ancistrus Kner, 1854 (Loricariidae, Ancistrini) from three hydrographic basins of Mato Grosso, Brazil

Abstract Populations of seven Ancistrus species were analyzed from streams and rivers of three hydrographic Brazilian basins. All populations showed different diploid numbers (2n), fundamental numbers (FNs), and karyotypes. Some representatives of Loricariidae have 2n = 54 chromosomes, which is very likely an ancestral cytotaxonomic characteristic, but many other representatives show extensive karyotype diversification. In the Ancistrus species studied, extensive karyotypic differentiation, which is generally associated with chromosome number reduction and rearrangement of the ribosomal RNA gene (rDNA) sites, was verified. Chromosomal locations of 18S and 5S rDNA were jointly detected using fluorescence in situ hybridization (FISH). In all the Ancistrus species analyzed, 18S rDNA sites were detected only on one chromosome pair, though this differed among species. 5S rDNA was located on 1–3 chromosome pairs either separately or in synteny with 18S rDNA in four of the seven species/populations. Hence the karyotype differentiation in Ancistrus species could be associated with a morphological speciation process, suggesting that chromosome fusions, inversions, deletions, duplications, and heterochromatination could contribute to the karyotype evolution of these neotropical armored catfishes.

Diversity and chromosomal evolution in the genus Ancistrus Kner, 1854 (Loricariidae: Ancistrini) from three hydrographic basins of Mato Grosso State, Brazil

Cytogenetic analyses were carried out in 117 specimens of seven species of the genus Ancistrus from three hydrographic in Mato Grosso State: Paraguay, Araguaia-Tocantins and Amazon basins. Conventional cytogenetic techniques were used to obtain mitotic chromosomes. C-banding was performed to detect heterochromatic regions and silver nitrate staining was used to identify nucleolar organizer regions (Ag-NORs). The counted and paired chromosomes revealed diploid numbers ranging from 2n = 40 to 2n = 54 with karyotype formulae varying from FN = 80 to FN = 86. Single marks in distinct chromosomes identified the nucleolar organizer regions. The constitutive heterochromatin was scarce in the diploid number from 2n = 50 to 2n = 54 and conspicuous blocks were observed in a single species with 2n = 40 chromosomes. These data corroborate the hypotheses of reduction of diploid number in species with derived features such as presence of sex chromosomes and polymorphisms, besides allowing inferences about the evolutionary mechanisms and the ancestor karyotype that favored the diversification of this important genus in the tribe Ancistrini.

Comparative cytogenetics of Astyanax (Teleostei: Characidae) from the upper Paraguay basin

Astyanax is one of the most abundant and diverse taxa of fishes in the Neotropical region. In order to increase the amount of cytogenetic information for Astyanax as well as to exhibit data to subsidize future taxonomic studies, this work analyzed three species of Astyanax: two species are cryptic, and are here reported to live in syntopy (A. abramis and A. lacustris); the first karyotype description for A. pirapuan is also presented. Cytogenetic analyzes reveal a diploid number of 2n=50 chromosomes for three species, yet with differences in their karyotype morphology. The physical mapping of 18S rDNA showed up to thirteen sites in A. pirapuan and two in A. abramis and A. lacustris. The physical mapping of 5S rDNA has proven to be an effective marker for the characterization of species of Astyanax studied in this work.

Phylogenetic and Phylogeographic Relationships among Lineages of the Armored Catfish Ancistrus Kner, 1854 (Loricariidae: Ancistrini), from the Amazon and Paraguay Basins

Ancistrus is one of the most diverse genera in the Ancistrini tribe, with 64 nominal species. The group is characterized by high cytogenetic variability; the diploid number of chromosomes ranges from 2n = 34 to 2n = 54. Ancistrus is widely distributed in the basins of the Uruguay, Paraguay, and Amazonian rivers; the latter two regions show the greatest diversity of Ancistrus species and karyotypes. Despite these characteristics, the group includes species for which taxonomic identification is difficult, and phylogenetic relationships and phylogeographic patterns, especially in the Paraguay and Amazon basins, have not yet been revealed. In this study, we determined the phylogenetic and phylogeographic relationships among the Ancistrus lineages in these regions. In particular, 93 concatenated sequences of mitochondrial ATPase 6/8 and COI as well as nuclear Rag2 were used for a phylogenetic analysis, and ATPase 6/8 were used for a phylogeographic analysis. The topology generated by the Bayesian method included three distinct clades subdivided into 21 groups. The clades indicated a monophyletic relationship among the lineages from the Amazon and Paraguay basins. The 21 groups had a high average genetic distance (8.4%) and were structured genetically. In the haplotype network, eight large groups were observed, seven belonging to the Paraguay basin and one corresponding to the Amazon basin, and no haplotypes were shared between the two basins. These results indicate that Ancistrus lineages form a monophyletic unit in the Paraguay and Amazon basins, and these lineages have a high level of divergence and genetic isolation. These results corroborate the existence of cryptic species in the region and emphasize the need for a taxonomic revision of the genus in these basins.

Chromosome mapping of a Tc1-like transposon in species of the catfish Ancistrus

Abstract The Tc1 mariner element is widely distributed among organisms and have been already described in different species of fish. The genus Ancistrus (Kner, 1854) has 68 nominal species and is part of an interesting taxonomic and cytogenetic group, as well as presenting a variation of chromosome number, ranging from 2n=34 to 54 chromosomes, and the existence of simple and multiple sex chromosome system and the occurrence of chromosomal polymorphisms involving chromosomes that carry the nucleolus organizer region. In this study, a repetitive element by restriction enzyme, from Ancistrus sp.1 “Flecha” was isolated, which showed similarity with a transposable element Tc1-mariner. Its chromosomal location is distributed in heterochromatic regions and along the chromosomal arms of all specimens covered in this study, confirming the pattern dispersed of this element found in other studies carried out with other species. Thus, this result reinforces the hypothesis that the sequence AnDraI is really a dispersed element isolated. As this isolated sequence showed the same pattern in all species which have different sex chromosomes systems, including in all sex chromosomes, we could know that it is not involved in sex chromosome differentiation.

Chromosome mapping of U2 snDNA element in two populations of Ancistrus sp (Siluriformes: Loricariidae)

Universidade Estadual Paulista Julio de Mesquita Filho, Instituto de Biociencias, Rio Claro, BrasilThe advent of the next generation sequencing (NGS) made sequencing and scaffolding of an entire animal genome a routine procedure. As the result we face a fast increase in the number of animal genomes available due to the activities of large international genome sequencing initiatives e.g., Genome 10K (G10K) or smaller projects. However, the full informative power of a sequenced genome could only be achieved when it is assembled into chromosomes. Usually, a draft or nearly complete animal chromosome assembly is achieved through three steps: (i) constructing contigs based on read overlaps, (ii) merging contigs into scaffolds using pair-end reads, and (iii) mapping scaffolds on chromosomes with the use of physical or genetic maps. As the cost of mapping techniques is still much higher than sequencing, the genetic and physical maps are not available for the majority of the de novo sequenced genomes. To overcome this problem for assemblies that employ long-insert libraries (5 – 40 Kbp) we recently developed the reference-assisted chromosome assembly (RACA) algorithm (Kim et al., 2013). This method relies on both the raw sequencing data (reads) and comparative information; the latter is obtained from alignments between the target (de novo sequenced), a closely related (reference) and more distantly related (outgroup) genomes. Using RACA followed by the manual FISH or PCR verification steps we are reconstructing the chromosome organisation of 19 bird species sequenced by the G10K community. We use the publically available chicken (Gallus gallus) and zebra finch (Taeniopygia guttata) chromosome assemblies as either reference or outgroup for each reconstruction depending on their phylogenetic relationships with each target species. Initially, we established the optimal RACA parameters for a bird chromosome assembly reconstruction using the duck (Anas platyrhynchos) and budgerigar (Melopsittacus undulatus) super-scaffolds assembled with the support from physical maps. This step allowed us to test the reliability of RACA reconstructions for bird genomes. Due to a higher evolutionary conservation of the bird karyotype compared to the mammalian one, we have achieved ~97% accuracy of scaffold adjacencies in our predicted chromosome fragments compared to the ~93-96% accuracies reported for mammals (Kim et al., 2013). We detected ~4-28% of scaffolds in different target bird genomes that are either chimeric or containing genuine lineage-specific evolutionary breakpoint regions. Some of these scaffolds will be selected for follow up PCR or FISH verifications. All RACA reconstructions will become publicly available from our Evolution Highway comparative chromosome browser http://evolutionhighway.ncsa.uiuc.edu/birds/ and will be further utilised to study connections between the chromosome evolution, adaptation and phenotypic diversity in birds and other vertebrates.Universidade Estadual Paulista, Nucleo de Pesquisa e Conservacao de Cervideos, Faculdade de Ciencias Agrarias e Veterinarias, Jaboticabal, Brasil• Invited speaker abstracts have the prefix “S” • Selected Oral presentations have the prefix “O” • Poster abstracts have the prefix “P” S1: 50th Anniversary of the first Oxford Chromosome Conference and some reflections on chromosome synapsis Malcolm A Ferguson-Smith Department of Veterinary Medicine, University of Cambridge, Cambridge, UK. Cyril Darlington, who organised the first Oxford Chromosome Conference 50 years ago, was one of the great pioneers of cytogenetics. He brought new understanding to the mechanisms of mitosis and meiosis and the uniformity of chromosome behaviour in all plants and animals with its implications for evolution. His major conclusions relate to the origin of chiasmata and the properties of sex chromosomes and were based on light microscopy before the era of molecular cytogenetics in the 1970s. Since his day the field has been transformed by electron microscopy, FISH, immunofluorescence of chromosomal proteins, meiotic mutants in yeast and mice and by DNA mapping and sequencing. Progress in understanding chromosome structure and synapsis in meiotic and somatic cells since Darlington will be briefly summarised with emphasis on the unknown. Genome conservation and the nature of non-coding DNA at synapsis sites, and the threedimensional structure of chromosomal proteins (eg, those of axial filaments), should be among the topics for discussion at this and future Chromosome Conferences. 20th International Chromosome Conference (ICCXX) 35120th International Chromosome Conference (ICCXX). 50th Anniversary, University of Kent, Canterbury, 1st–4th September 2014.Dinosaurs hold a unique place both in the history of the earth and the imagination of many. They dominated the terrestrial environment for around 170 million years during which time they diversified into at least 1000 different species. Reptilia, within which they are placed is one of the most remarkable vertebrate groups, consisting of two structurally and physiologically distinct lineages – the birds and the non-avian reptiles, of which there are 10,000 and 7,500 extant species respectively. The dinosaurs are without doubt the most successful group of vertebrate to have existed. They survived several mass extinction events before finally non-avian dinosaurs were defeated 66 million years ago in the Cretaceous-Paleogene extinction event, leaving the neornithes (modern birds) as their living descendants. Aside from the huge phenotypic diversity seen in this group, the birds and non-avian reptiles interestingly display similar karyotypic patterns (with the exception of crocodilians); with the characteristic pattern of macro and micro chromosomes, small genome size and few repetitive elements, suggesting that these were features exhibited in their common ancestor. In this study, the availability of multiple reptile genome sequences (including birds) on an interactive browser (Evolution Highway) allowed us to identify multi species homologous synteny blocks (msHSBs) between the putative avian ancestor (derived from six species of extant birds), the Lizard (Anolis carolensis) and the Snake (Boa constrictor). From these msHSBs we were able to produce a series of contiguous ancestral regions (CARs) representing the most likely ancestral karyotype of the Saurian (ancestor of archosaurs and lepidosaurs) that diverged from the mammalian lineage 280 mya. From this we have hypothesised the series of inter and intra-chromosomal rearrangements that have occurred along the dinosaur (archosaur) lineage to the ancestor of modern birds (100 mya) and along the lepidosaur lineage to the modern snake and lizard using the model of maximum parsimony. Our study shows that relatively few chromosomal rearrangements took place over this period with an average of one inter or intra-chromosomal (translocations and inversions respectively) rearrangement occurring approximately every 2 million years. The majority of these rearrangements appear to be intra-chromosomal suggesting an overall karyotypic stability, which is consistent with that of that of modern birds. Our results support the hypothesis that the characteristically avian genome was present in the saurian ancestor and that it has remained remarkably stable in the 280 million years since. It is credible therefore to suggest that this ‘avian-style’ genome may be one of the key factors in the success of this extraordinarily diverse animal group.