Cytogenetic Characterization of Geophagus brasiliensis and Two Species of Gymnogeophagus (Cichlidae: Geophaginae) from Guaíba Lake, RS, Brazil

Chromosome comparison among five species of Neotropical cichlids of Cichlasoma and Gymnogeophagus (Perciformes)

The genera Cichlasoma and Gymnogeophagus belong to the subfamily Cichlinae, the only one in Neotropical cichlids. Cichlasoma dimerus, C. paranaense, C. portalegrense, Gymnogeophagus rhabdotus, and G. lacustris were collected at different points in the Paranapanema and Paraguay basins and the Lagoon of Patos hydrographic system. In addition to conventional analysis, CMA3 fluorochrome staining, and FISH with 18S rDNA probe were performed. All species had a diploid number equal to 48, with interand intraspecific differences in karyotype formulae. All species presented a single AgNOR site, except G. rhabdotus and the C. paranaense population of the Paranapanema River, which revealed more than one pair of nucleolar chromosomes. AgNORs were coincident to 18S rDNA and CMA3. Heterochromatin was distributed in the pericentromeric chromosomal regions and coincident with NORs. For the first time, this work shows cytogenetic data for C. portalegrense, G. lacustris, and G. rhabdotus. Although some results reinforce the idea of conservative chromosome evolution of 2n in Cichlinae, interspecific and populational variations observed confirm that chromosomal rearrangements affect the microstructural karyotype diversification in this group of fish.

Extensive Chromosomal Reorganization in Apistogramma Fishes (Cichlidae, Cichlinae) Fits the Complex Evolutionary Diversification of the Genus

Neotropical cichlid fishes are one of the most diversified and evolutionarily successful species assemblages. Extremely similar forms and intraspecific polychromatism present challenges for the taxonomy of some of these groups. Several species complexes have a largely unknown origin and unresolved evolutionary processes. Dwarf cichlids of the genus Apistogramma, comprising more than a hundred species, exhibit intricate taxonomic and biogeographic patterns, with both allopatric and sympatric distributions. However, karyotype evolution and the role of chromosomal changes in Apistogramma are still unknown. In the present study, nine South American Apistogramma species were analyzed using conventional cytogenetic methods and the mapping of repetitive DNA sequences [18S rDNA, 5S rDNA, and (TTAGGG)n] by fluorescence in situ hybridization (FISH). Our results showed that Apistogramma has unique cytogenetic characteristics in relation to closely related groups, such as a reduced 2n and a large number of bi-armed chromosomes. Interspecific patterns revealed a scenario of remarkable karyotypic changes, including a reduction of 2n, the occurrence of B-chromosomes and evolutionary dynamic of rDNA tandem repeats. In addition to the well-known pre-zygotic reproductive isolation, the karyotype reorganization in the genus suggests that chromosomal changes could act as postzygotic barriers in areas where Apistogramma congeners overlap.

Karyotype diversity between species of Crenicichla (Perciformes, Cichlidae) from different Brazilian hydrographic basins

Crenicichla is the largest genus in the Cichlidae family in South America. The genus includes 100 valid species that are popularly known in Brazil as jacundás or joaninhas and are widely distributed in rivers east of the Andes. Cytogenetic analyses were carried out on seven species in this genus. All species showed a diploid number of 48 with interspecific differences in karyotype formulas and AgNORs located in interstitial position on the short arm of the largest metacentric pair, except for the two populations from C. britskii. Population A showed terminal markings on the long arm of the fifth pair of the complement, and population B showed up to two marked chromosome pairs. FISH with an 18S rDNA probe was coincident with AgNORs and CMA₃, except for pair 6 from population B of C. britskii that did not presented positive CMA₃ sites. This work presents first cytogenetic data for C. haroldoi, C. maculata, and C. punctata, and the results show karyotypic patterns similar to those in the literature. However, the diversity found in populations of C. britskii represents new information about the evolution of the karyotype of the Cichlidae family, which has been conservative. Furthermore, the data could assist in phylogenetic studies of Crenicichla.

On the tear proteome of the house mouse (Mus musculus musculus) in relation to chemical signalling

Mammalian tears are produced by lacrimal glands to protect eyes and may function in chemical communication and immunity. Recent studies on the house mouse chemical signalling revealed that major urinary proteins (MUPs) are not individually unique in Mus musculus musculus. This fact stimulated us to look for other sexually dimorphic proteins that may—in combination with MUPs—contribute to a pool of chemical signals in tears. MUPs and other lipocalins including odorant binding proteins (OBPs) have the capacity to selectively transport volatile organic compounds (VOCs) in their eight-stranded beta barrel, thus we have generated the tear proteome of the house mouse to detect a wider pool of proteins that may be involved in chemical signalling. We have detected significant male-biased (7.8%) and female-biased (7%) proteins in tears. Those proteins that showed the most elevated sexual dimorphisms were highly expressed and belong to MUP, OBP, ESP (i.e., exocrine gland-secreted peptides), and SCGB/ABP (i.e., secretoglobin) families. Thus, tears may have the potential to elicit sex-specific signals in combination by different proteins. Some tear lipocalins are not sexually dimorphic—with MUP20/darcin and OBP6 being good examples—and because all proteins may flow with tears through nasolacrimal ducts to nasal and oral cavities we suggest that their roles are wider than originally thought. Also, we have also detected several sexually dimorphic bactericidal proteins, thus further supporting an idea that males and females may have adopted alternative strategies in controlling microbiota thus yielding different VOC profiles.

Comparative Cytotaxonomy of Two Species of Fish from the Genus Satanoperca Reveals the Presence of a B Chromosome

The taxonomy of Satanoperca spp. is still unresolved, especially because coloring, one of the main diagnostic characters, is variable among species of this genus. Thus, the aim of this study was to elucidate the relationship between the genome and the organization of the chromosome in two Satanoperca species. Our main goal was to develop a method to better differentiate taxa and understand the evolution of Satanoperca jurupari and Satanoperca lilith karyotypes, which we analyzed with classical and molecular cytogenetics. Both species have the same diploid number (2n) of 48 and location of 5S rDNA sites on pair 5. Nonetheless, the distribution of heterochromatin and 18S rDNA sites followed a species-specific pattern. The interstitial telomeric sites were not highlighted in either species. Regardless, a single B chromosome was identified in some metaphases of S. lilith. These data show that Satanoperca species harbor chromosomal features that can be used to identify the two species of Satanoperca studied here, allowing for the use of cytogenetic markers to make taxonomic inferences within the genus.

Cryptic speciation within the Neotropical cichlid Geophagus brasiliensis (Quoy & Gaimard, 1824) (Teleostei Cichlidae): a new paradigm in karyotypical and molecular evolution

The family Cichlidae is one of the most species-rich taxa in the Neotropics. However, the factors that determine these high levels of biodiversity remain unexplored. We have analyzed the morphological, cytogenetic, and molecular data from 62 specimens of a widespread cichlid, Geophagus brasiliensis, from three adjacent basins in southeastern Brazil. Morphological analyses did not show differences among specimens. The cytogenetic data indicate the occurrence of multiple nucleolar organizer regions and four sympatric karyotypes that differ in the first pair of chromosome morphology, in the Doce River Basin; whereas the karyotype from the Paraíba do Sul Basin is widely divergent. The molecular data--616 bp fragment of cytochrome oxidase subunit I--revealed two haplogroups with the deepest genetic divergence (6.4%) ever reported within a nominal species in the Neotropical Region: One of the haplogroups is restricted to the quaternary lakes in the middle portion of the Doce Basin and the Mucuri River, whereas the other haplogroup is composed of haplotypes from elsewhere in the Doce Basin and the Paraíba do Sul Basin. These patterns suggest that G. brasiliensis undergoes a cryptic speciation process involving three major lineages that differ from the African explosive cichlid radiation.

Comparative cytogenetics of ten species of cichlid fishes (Teleostei, Cichlidae) from the Araguaia River system, Brazil, by conventional cytogenetic methods

Cichlids represent one of the most species-rich families of fishes and have attracted the attention of evolutionary biologists due to the rapid radiation occurring in some groups and the importance of some species in the world aquaculture. Cytogenetic analysis was conducted in 10 cichlid species from the Araguaia River, Amazon Basin, Brazil. The chromosome number was 2n=48 for all analyzed species except for Laetacara araguaiae Ottoni et Costa, 2009 (2n=44). Chromosomal polymorphism was detected only in Geophagus proximus (Castelnau, 1855), which exhibits an extra large submetacentric and and a dot-like chromosomes. Moreover, the C-banding revealed a general pericentromeric heterochromatic pattern and some additional blocks for some species. The heterochromatic blocks corresponding to AgNOR bearing regions were observed in all species and also corresponded to CMA3 positive blocks, which were observed in terminal regions. Besides the general conserved chromosomal and heterochromatin patterns for South American cichlids, the presence of GC-rich heterochromatin was quite different in the species Biotodoma cupido (Heckel, 1840), Geophagus proximus, Retroculus lapidifer (Castelnau, 1855), Crenicichla strigata Günther, 1862 and Heros efasciatus Heckel, 1840. The results suggest that independent events of heterochromatin modification occurred during chromosome evolution in the group, regardless of the conservation of macro-chromosomal structure.

Chromosome differentiation patterns during cichlid fish evolution

BACKGROUND

Cichlid fishes have been the subject of increasing scientific interest because of their rapid adaptive radiation which has led to an extensive ecological diversity and their enormous importance to tropical and subtropical aquaculture. To increase our understanding of chromosome evolution among cichlid species, karyotypes of one Asian, 22 African, and 30 South American cichlid species were investigated, and chromosomal data of the family was reviewed.

RESULTS

Although there is extensive variation in the karyotypes of cichlid fishes (from 2n = 32 to 2n = 60 chromosomes), the modal chromosome number for South American species was 2n = 48 and the modal number for the African ones was 2n = 44. The only Asian species analyzed, Etroplus maculatus, was observed to have 46 chromosomes. The presence of one or two macro B chromosomes was detected in two African species. The cytogenetic mapping of 18S ribosomal RNA (18S rRNA) gene revealed a variable number of clusters among species varying from two to six.

CONCLUSIONS

The karyotype diversification of cichlids seems to have occurred through several chromosomal rearrangements involving fissions, fusions and inversions. It was possible to identify karyotype markers for the subfamilies Pseudocrenilabrinae (African) and Cichlinae (American). The karyotype analyses did not clarify the phylogenetic relationship among the Cichlinae tribes. On the other hand, the two major groups of Pseudocrenilabrinae (tilapiine and haplochromine) were clearly discriminated based on the characteristics of their karyotypes. The cytogenetic mapping of 18S ribosomal RNA (18S rRNA) gene did not follow the chromosome diversification in the family. The dynamic evolution of the repeated units of rRNA genes generates patterns of chromosomal distribution that do not help follows the phylogenetic relationships among taxa. The presence of B chromosomes in cichlids is of particular interest because they may not be represented in the reference genome sequences currently being obtained.