Astyanax fasciatus may be characterized as a chromosomally diversified ‘species’ presenting distinct cytotypes, each with its specific variants. The sympatric and syntopic occurrence of different cytotypes reinforces the hypothesis in which A. fasciatus may represent a group of species currently placed under a single common designation. Specimens from three collection points spread along the Mogi-Guaçu River in southeast Brazil were examined in the present work: (1) near its headwaters (Ouro Fino – MG), (2) in the middle region of the river (Cachoeira de Emas, Pirassunun ga – SP) and (3) close to its confluence with the Pardo River (Barrinha – SP). The 2n = 48 chromosomes cytotype was found in all sampling points, while cytotype 2n = 46 was only encountered in Barrinha and Cachoeira de Emas. In the latter locality, cytotype 2n = 46 predominated; nevertheless, other karyotype forms with 2n = 45 and 47 chromosomes also occurred, besides a structural variant of cytotype 2n = 46. One specimen with 2n = 47 chromosomes was also found in Ouro Fino. The Ag-NOR analysis, as well as the location of the 18S and 5S ribosomal genes, were conserved in all cytotypes. The data indicate that the variant karyotypes are a consequence of interbreeding between the standard cytotypes (2n = 46 and 48) and/or its descendants. This suggests a karyotype plasticity for this species, where at least a few variant karyotypes would not have deleterious effects on their bearers.

We present cytogenetic analyses of four fish species, belonging to four Loricariidae subfamilies: Neoplecostomus microps (Neoplecostominae) with 2n ¼ 54 chromosomes, Harttia loricariformis (Loricariinae) with 2n ¼ 56 chromosomes, Hypostomus affinis (Hypostominae) with 2n ¼ 66 chromosomes and Upsilodus sp. (Upsilodinae), with 2n ¼ 96 chromosomes. In addition to karyotypes, data on the location of 18s rDNA sites are presented, derived from indirect (silver nitrate impregnation) and direct (FISH) methods. There is only one pair of nucleolar organizing regions (NORs) per species, except in H. affinis. Diversity and NOR macrokaryotypic evolution in the species analyzed are discussed in relation to the evolution of the Loricariidae as a whole. In addition, a revision of the cytogenetic data available for this family is presented.

The use of improved cytogenetic techniques such as fluorescent in situ hybridization (FISH) has offered important methodologies for cytotaxonomic and evolutionary studies. In particular, the mapping of 5S rDNA sites has proved to be an excellent marker in the study of different organisms and, more recently, in fish. In the present work, the FISH technique was used to map the 5S rDNA sites in the chromosomes of eight neotropical fish species from the Paraíba do Sul river basin, four of these belonging to the order Characiformes, family Characidae, genus Astyanax (A. scabripinnis, A. parahybae, A. giton and A. intermedius) and four to the order Siluriformes, family Loricariidae (Neoplecostomus microps, Harttia loricariformis, Hypostomus affinis and Upsilodus sp.). Karyotype evolution aspects of the analyzed groups are discussed.

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Regarding such an important issue as our origin, as well as the origin of all biological diversity, it is surprising to realize that evolution still faces drawbacks in keeping its deserved notability as a unifying theory in biology. This does not happen because evolutionism lacks validity as a scientific theory, but rather because of several misconceptions regarding evolutionary biology that were and continue to be found in elementary and secondary education. Furthermore, mistaken evolutionary ideas also affect some philosophical and social issues. The aim of the present study was to evaluate knowledge about evolution among freshman students from distinct majoring areas at Universidade Estadual do Centro-Oeste do Paraná (UNI-CENTRO), Brazil. The research was carried out based on a ten-question questionnaire about evolution with distinct levels of difficulty, comprising the most observed misconceptions. In this study, 231 students attending classes in biological sciences (morning and evening schedule), exact sciences (agronomy, physics, chemistry, and math), and human sciences (history, geography, and pedagogy) were interviewed. The total average of right answers was 48.8%, and the highest average per course obtained was 58.7% from the students attending biological sciences (evening schedule). Although evolutionary biology and ecology are supposed to represent teaching guide issues according to the recommendations of the National Curricular Parameters for the Secondary School, the data obtained suggest that the evidence for evolution, the role of natural selection and random events, as well as the sources of variation, must be better focused at schools.