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The Amazon aquatic ecosystems have been modified by the human population growth, going through changes in their water bodies and aquatic biota. The spectacled alligator (Caiman crocodilus crocodilus) has a wide distribution and adaptability to several environments, even those polluted ones. This study aimed to investigate if a Caiman species living in urban streams of Manaus city (Amazonas State, Brazil) is affected by environmental pollution. For that, it was used classical and molecular cytogenetic procedures, in addition to micronucleus and comet assays. Although the karyotype macrostructure remains unaltered (2 n = 42 chromosomes; 24 t + 18 m/sm; NF = 60), the genotoxic analysis and the cytogenetic mapping of repetitive DNA sequences demonstrated that polluted environments alter the genome of the specimens, affecting both the chromosomal organization and the genetic material., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Pollution is a growing environmental problem throughout the world, and the impact of human activities on biodiversity and the genetic variability of natural populations is increasingly preoccupying, given that adaptive processes depend on this variability, in particular that found in the repetitive DNA. In the present study, the mitochondrial DNA (COI) and the distribution of repetitive DNA sequences (18S and 5S rDNA) in the fish genome were analysed in fish populations inhabiting both polluted and unpolluted waters in the northern Amazon basin. The results indicate highly complex ribosomal sequences in the fish genome from the polluted environment because these sequences are involved primarily in the maintenance of genome integrity, mediated by a systematic increase in the number of copies of the ribosomal DNA in response to changes in environmental conditions., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The genera Leptodactylus and Adenomera comprise 92 species distributed throughout the Neotropical region. These species have a modal diploid chromosome number 2n = 22. However, chromosome rearrangements are evident in the differentiation of five intra-generic groups in the genus Leptodactylus (L. fuscus, L. latrans, L. marmoratus (formally composed by the species of the genus Adenomera), L. melanonotus, L. pentadactylus), yet it is not clear if there is a karyotype pattern for each group. Aiming to understand the intra-generic and interspecific karyotype patterns of Leptodactylus and Adenomera, cytogenetic analyses were performed in A. andreae, L. macrosternum, L. pentadactylus, L. petersii, and L. riveroi using conventional staining, C-banding, nucleolus organizer region (NOR) and hybridization in situ fluorescent (FISH). The karyotype of Leptodactylus riveroi was described for the first time. Adenomera andreae had 2n = 26, while the remaining species 2n = 22. The NOR was found on pair No. 8 of A. andreae, L. macrosternum, L. pentadactylus, and L. riveroi, whereas L. petersii had it on pairs Nos. 6 and 10. These locations were confirmed by the FISH with 18S rDNA probe, except for pair No. 10 of L. petersii. The C-banding pattern was evident at the centromeres of chromosomes of all species and some interspecific variations were also observed. 2n = 22 was observed in the species of the L. latrans group, as well as in the intra-generic groups L. fuscus and L. pentadactylus; in the L. melanonotus group there were three diploid chromosome numbers 2n = 20, 22 and 24; and a larger variation in 2n was also evident in the L. marmoratus group.

Repetitive DNA is the largest fraction of the eukaryote genome and comprises tandem and dispersed sequences. It presents variations in relation to its composition, number of copies, distribution, dynamics, and genome organization, and participates in the evolutionary diversification of different vertebrate species. Repetitive sequences are usually located in the heterochromatin of centromeric and telomeric regions of chromosomes, contributing to chromosomal structures. Therefore, the aim of this study was to physically map repetitive DNA sequences (5S rDNA, telomeric sequences, tropomyosin gene 1, and retroelements Rex1 and SINE) of mitotic chromosomes of Amazonian species of teiids (Ameiva ameiva, Cnemidophorus sp. 1, Kentropyx calcarata, Kentropyx pelviceps, and Tupinambis teguixin) to understand their genome organization and karyotype evolution. The mapping of repetitive sequences revealed a distinct pattern in Cnemidophorus sp. 1, whereas the other species showed all sequences interspersed in the heterochromatic region. Physical mapping of the tropomyosin 1 gene was performed for the first time in lizards and showed that in addition to being functional, this gene has a structural function similar to the mapped repetitive elements as it is located preferentially in centromeric regions and termini of chromosomes., (© 2016 S. Karger AG, Basel.)

Background: Hypsiboas species have been divided into seven groups using morphological and genetic characters, but for most of the species, there is no cytogenetic information available. A cytogenetic analysis using conventional staining, C-banding, silver staining, and fluorescence in situ hybridization (FISH) with telomeric sequence probes were used to investigate the karyotype of seven Amazon species of the genus Hypsiboas belonging to the following intrageneric groups: H. punctatus (H. cinerascens), H. semilineatus (H. boans, H. geographicus, and H. wavrini), and H. albopunctatus (H. lanciformis, H. multifasciatus, and H. raniceps). The aim was to differentiate between the karyotypes and use the chromosomal markers to distinguish between the Hypsiboas groups. The data were compared with a previous phylogenetic proposal for these anurans. In addition, H. lanciformis, H. boans, and H. wavrini are described here for the first time, and we characterize the diploid numbers for H. cinerascens, H. geographicus, H. multifasciatus, and H. raniceps., Results: The diploid number for all of the species analyzed was 24, with the exception of Hypsiboas lanciformis, which had 2n = 22 chromosomes. The constitutive heterochromatin distribution, nucleolar organizer region locations, and interstitial telomeric sites differed between the species. A hypothesis that the heterochromatic patterns are evolving is proposed, with the divergence of the groups probably involving events such as an increase in the heterochromatin in the species of the H. semilineatus group. The FISH conducted with the telomeric probes detected sites in the terminal regions of all of the chromosomes of all species. Interstitial telomeric sites were detected in three species belonging to the H. semilineatus group: H. boans, H. geographicus, and H. wavrini., Conclusion: The results of this study reinforce the complexity previously observed within the genus Hypsiboas and in the different groups that compose this taxon. More studies are needed focusing on this group and covering larger sampling areas, especially in the Brazilian Amazon, to improve our understanding of this fascinating and complex group.

Tandemly repeated sequences are a common feature of vertebrate mitochondrial DNA control regions. However, questions still remain about their mode of evolution and function. To better understand patterns of variation in length and to explore the existence of previously described domain, we have characterized the control region structure of the Amazonian ornamental fish Nannostomus eques and Nannostomus unifasciatus. The control region ranged from 1121 to 1142 bp in length and could be separated into three domains: the domain associated with the extended terminal associated sequences, the central conserved domain, and the conserved sequence blocks domain. In the first domain, we encountered a sequence repeated 10 times in tandem (variable number tandem repeat (VNTR)) that could adopt an "inverted repetitions" type structural conformation. The results suggest that the VNTR pattern encountered in both N. eques and N. unifasciatus is consistent with the prerequisites of the illegitimate elongation model in which the unequal pairing of the chains near the 5'-end of the control region favors the formation of repetitions.

Mitochondrial DNA ( mtDNA) sequences of the marbled hatchetfish Carnegiella strigata, an ornamental fish exported from the Negro River, was examined to determine its genetic diversity and population structure in blackwater rivers (Negro and Uatumã Rivers) in the central Amazon. Analyses of a 646 bp fragment of the ATPase 6/8 mtDNA gene revealed two monophyletic lineages of C. strigata with considerable genetic distance between them (10-12%), suggesting that these lineages should not be considered a single stock. Furthermore, there were strong differences in the geographical distribution of the lineages. These results indicate a past association between drainages of the Negro and Uatumã Rivers. They also suggest that, in the Negro River, its main tributary, the Branco River, may act as a geographical barrier and potentially an ecological barrier between populations of the middle and lower portions of the river., (© 2012 The Authors. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles.)

The genetic variability of the brown pencilfish Nannostomus eques was studied, based on an analysis of sequences from the control region (1084 bp) of mitochondrial (mt)DNA in 125 individuals collected from eight tributaries along the upper (Açaituba, Miuá, Jaradi and Arixanã), middle (Demini), and lower (Jacundá, Maguari and Catalão) Rio Negro (Brazil). Phylogenetic inferences using mtDNA data from N. eques revealed two evolutionary units. Genetic distance between them ranged from 5.5 to 8.3% and differed by 8.5-11.8% from the sister species pencilfish Nannostomus unifasciatus. The time of divergence between the two evolutionary units was estimated to be the Middle Pliocene (c. 2.99 million years before present). Population genetic analysis (DNA polymorphism, AMOVA and Mantel test) showed high haplotype diversity (HD, >0.90) in each evolutionary unit, a strong population genetic structure in the Demini River that formed a monophyletic group and a correlation between genetic divergence and geographical distance in only one of these units (evolutionary unit 1). On the basis of molecular data, the rapids and waterfalls near São Gabriel da Cachoeira (Upper Rio Negro) were the main barriers to gene flow within evolutionary unit 1 in some localities. The emergences of the Branco River and the Anavilhanas Archipelago were apparently responsible for the discrepancy in distribution of the two evolutionary units, except at Jacundá, where the evolutionary units were sympatric. In view of the differences between the evolutionary units, N. eques cannot be treated as a single stock in the Rio Negro basin. These results may have important implications for the fishery management of this ornamental fish., (© 2012 The Authors. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles.)