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The absence of monogenean parasites in fish is a rare and intriguing occurrence in natural populations, often raising important questions about the environmental and biological factors at play. In this study, we focused on the gill ectoparasites of the Neotropical characid Psalidodon aff. fasciatus, the sole fish species inhabiting an isolated lake, millions of years old, located within a sinkhole in southern Brazil. A sinkhole is a steep, deep depression in the ground that forms a lake disconnected from other bodies of water, creating a unique and highly isolated environment. Over the span of a year, we examined 123 individual fish from this environment and found no ectoparasites on their gills. This striking absence of parasites reveals a complex scenario of evolutionary adaptations, potentially influenced by the isolated nature of the ecosystem. These findings challenge conventional perspectives on species interactions and parasitism, providing new insights into how organisms adapt to specific environmental conditions and prolonged isolation. [ABSTRACT FROM AUTHOR]

Research on the dynamics of vegetation distribution in relation to past climate can provide valuable insights into terrestrial ecosystems’ response to climate change. However, paleoenvironmental data sources are often scarce. The integration of ecological niche modeling and paleoecological data can fill in this knowledge gap. In order to elucidate the potential impacts of past and future climate change on the distribution of multiple vegetation types, we used 433 occurrence points of 100 species to build distribution models of five vegetation types occurring in southern Brazil, based on past, current, and future scenarios. Past models indicated the existence of a steppe domain during the Last Glacial Maximum, with forest expansion during the Mid-Holocene, which is consistent with paleoenvironmental data. The current distribution model identified a large area that was climatically suitable for ecotones in an important protection area threatened by agribusiness. The optimistic projections for 2070 predicted an expansion of mixed ombrophilous and seasonal semi-deciduous forests to a higher altitude and latitude, respectively. The pessimistic projections predicted a catastrophic scenario, with the extinction of the steppe and the savanna and a major increase of areas unsuitable for all vegetation types. The ombrophilous dense forest remained stable in all time scenarios, even in the pessimistic future projection. The results of the present study reinforce the need for the implementation of policies that will reduce greenhouse gas emissions that drive global climate change, which may lead to the extinction not only of species but also of landscapes as we know them today. [ABSTRACT FROM AUTHOR]

The taxonomy of the family Parodontidae is confused, with many open questions regarding the most appropriate generic groupings. Studies on the organization, structure, composition, and in situ location of chromosomal features have led to consistent advances in the understanding of genome evolution. Among the species of Parodontidae, the consistent chromosomal divergences can be helpful in taxonomic classification, such as heteromorphic chromosome sex, karyotypic formulae, and number/location of the repetitive DNAs. Molecular analysis of repetitive sequences of satellite DNA and their physical mapping in the chromosomes of different species in a single group may be used to infer evolutionary divergence and cladistic grouping. In the present study, rDNA and the satellite DNA pPh2004 were mapped by fluorescent in situ hybridization on the chromosomes of some species of Parodontidae. These results were analyzed and reviewed together with other chromosomal markers and previously published data, to formulate inferences about the diversification of the genomes and propose a clustering of some Parodontidae species. This analysis indicated that the species Apareiodon affinis, Parodon moreirai, Parodon hilarii, Parodon nasus, and Parodon pongoensis have an apomorphic state for satellite DNA pPh2004 in Parodontidae in relation to previously studied species of Apareiodon. [ABSTRACT FROM AUTHOR]

Fifty-five specimens of Steindachneridion melanodermatum were analyzed using molecular and conventional cytogenetic tools. Two polymorphisms were found: one involving the length of nucleolar organizer regions and another involving two submetacentric chromosomes previously identified as sex chromosomes. The polymorphism was confirmed by homogeneity between male and female karyotypes. Nucleotide sequencing and physical chromosome mapping were also used to identify and characterize one class of repetitive DNA, named SmAluI- Rex3. Based on the results and literature the present study offers an update of the occurrence of sex chromosome system in this species. [ABSTRACT FROM AUTHOR]

The freshwater silver catfish from the genus Rhamdia belongs to a group of neotropical fish with wide distribution throughout Central and South America. The results obtained in the F1 generation of native specimens of this species bred in captivity using molecular cytogenetic tools revealed a high number of triploid specimens (46.8%) in the samples analyzed. The use of double fluorescent in situ hybridization (double-FISH) with 18S and 5S rDNA probes allowed highlighting the location of ribosomal sites with independent activity. This chromosome marker allowed the identification of triploid nuclei, in which three markers were visualized, in contrast to diploid fish, which only exhibited two fluorescent signals. As triploid specimens exhibit either total or partial gonad sterility, the present study demonstrates the importance of cytogenetic monitoring in restocking programs aimed at genetic conservation. [ABSTRACT FROM AUTHOR]

Chromosome analyses were carried out for several fish species in a region impacted by the connection between two hydrographic basins, where a river originally pertaining to the Paraná River basin was transposed to the São Francisco River basin in the state of Minas Gerais, Brazil. The purpose was to assess the dispersal of invasive species from one hydrographic basin to the other and the consequent new geographical distributions of species that had been previously isolated from each other. Species of the families Parodontidae ( Apareiodon piracicabae, A. ibitiensis, Parodon hilarii, and P. nasus), Sternopygidae ( Eigenmannia virescens), and Gymnotidae ( Gymnotus sylvius) were studied. The four species of Parodontidae had 2n = 54 chromosomes, but species-specific karyotype structures, including the presence of the ZZ/ZW sex chromosome system in A. ibitiensis and P. hilarii. Two distinct karyomorphs (A and B) were identified for E. virescens, although with the same diploid number (2n = 38 chromosomes). G. sylvius had 2n = 40 chromosomes. P. hilarii and E. virescens (karyomorph B) are considered to be native to the São Francisco River basin, whereas A. piracicabae, A. ibitiensis, E. virescens (karyomorph A), and G. sylvius are known for the Paraná River basin, and P. nasus is known for the Paraná-Paraguay basin. The presence of the last five species in the São Francisco River basin indicates that they migrated from the Parana River to the São Francisco River basin due to the transposition of the river, and can therefore be considered invasive species in this basin. Moreover, a natural migratory pathway through the former wetland may have affected this dispersal. [ABSTRACT FROM AUTHOR]

Genetic variations in Astyanax sp. fish from Vila Velha State Park and Tibagi river (Paraná, Brazil) were analyzed by RAPD. Intrapopulational genetic similarity was analyzed at three collection sites. The higher RAPD polymorphism observed at site 3 (Tibagi river) suggests either an overlapping of structured populations or the presence of coexisting morphotypes at this site. Significant p values obtained by homogeneity tests revealed an unequal loci proportion among populations. The significance of similarity coefficients indicated that the differences observed among populations are relevant. These findings provide important information for the management and conservation of the species analyzed and for genetic variability maintenance programs. [ABSTRACT FROM AUTHOR]

Notopteridae (Teleostei, Osteoglossiformes) represents an old fish lineage with ten currently recognized species distributed in African and Southeastern Asian rivers. Their karyotype structures and diploid numbers remained conserved over long evolutionary periods, since African and Asian lineages diverged approximately 120 Mya. However, a significant genetic diversity was already identified for these species using molecular data. Thus, why the evolutionary relationships within Notopteridae are so diverse at the genomic level but so conserved in terms of their karyotypes? In an attempt to develop a more comprehensive picture of the karyotype and genome evolution in Notopteridae, we performed comparative genomic hybridization (CGH) and cross-species (Zoo-FISH) whole chromosome painting experiments to explore chromosome-scale intergenomic divergence among seven notopterid species, collected in different African and Southeast Asian river basins. CGH demonstrated an advanced stage of sequence divergence among the species and Zoo-FISH experiments showed diffuse and limited homology on inter-generic level, showing a temporal reduction of evolutionarily conserved syntenic regions. The sharing of a conserved chromosomal region revealed by Zoo-FISH in these species provides perspectives that several other homologous syntenic regions have remained conserved among their genomes despite long temporal isolation. In summary, Notopteridae is an interesting model for tracking the chromosome evolution as it is (i) ancestral vertebrate group with Gondwanan distribution and (ii) an example of animal group exhibiting karyotype stasis. The present study brings new insights into degree of genome divergence vs. conservation at chromosomal and sub-chromosomal level in representative sampling of this group. [ABSTRACT FROM AUTHOR]

Background: Among Neotropical fishes, the family Characidae is highly diverse and speciose and its taxonomy is not completely resolved. In Chile, the family is represented by five species, all within the genus Cheirodon, of which C. pisciculus, C. galusdae, C. kiliani, and C. australe are endemic, while C. interruptus is introduced. We compared chromosomal markers in order to appreciate the taxonomy and evolution of these trans-Andean fishes. Results: The specimens were photographed in stereomicroscope to observe the ventral protrusive teeth and cusps for morphological analysis and species identification. All of the species analysed had equally diploid chromosome number 2n = 50, with karyotypes dominated by high number of acrocentric chromosomes as compared to those of other members of Cheirodontinae. The distribution of heterochromatin was inconspicuous and was similar in all the species. The number of active NORs (nucleolus organizer regions) was polymorphic, with the greater number of them in C. kiliani and C. galusdae. The location of 5S and 18S rDNA ranged in number and position, showing two sites in different chromosomes. The fluorescent in situ hybridization with telomeric probe did not reveal interstitial sites in all analysed species. Conclusions: The comparative analysis of karyotypes and morphological markers revealed a biogeographic pattern of distribution, with the species that occur in the southern region forming one group and those in central and northern Chile forming another. [ABSTRACT FROM AUTHOR]