Chromosome evolution in fish: sex chromosome variability in Eigenmannia virescens (Gymnotiformes : Sternopygidae)

New data are presented on the sex chromosomes of the fish species Eigenmannia virescens (Gymnotiformes, Sternopygidae). A new finding, involving the occurrence of ZZ/ ZW sex chromosomes, is described in specimens sampled from the Sao Francisco and Amazon river basins in Brazil. All individuals had a chromosome number of 2n = 38. The homologs of the sex chromosome pair from the Sao Francisco river basin sample differed only in their morphology, while those from the Amazonian sample differed both in morphology and heterochromatin pattern. A possible model for the evolution of the sex chromosomes in E virescens is proposed, including data from populations from the Parana (Brazil) river basin, in which male heterogamety has already been described. The occurrence of different sex chromosome systems in species and populations of the neotropical freshwater fish fauna is discussed. Copyright (C) 2002 S. Karger AG, Basel.

Sex chromosome evolution in fish: the formation of the neo-Y chromosome in Eigenmannia (Gymnotiformes)

Chromosomes of a species of Eigenmannia presenting a X1X1X2X2:X1X2Y sex chromosome system, resulting from a Y-autosome Robertsonian translocation, were analyzed using the C-banding technique, chromomycin A(3) (CMA(3)) and mithramycin (MM) staining and in situ digestion by the restriction endonuclease AluI. A comparison of the metacentric Y chromosome of males with the corresponding acrocentrics in females indicated that a C-band-positive, CMA(3)/MM-fluorescent and AluI digestion-resistant region had been lost during the process of translocation, resulting in a diminution of heterochromatin in the males. It is hypothesized that the presence of a smaller amount of G+C-rich heterochromatin in the sex chromosomes of the heteromorphic sex when compared with the homomorphic sex may be associated with the sex determination mechanism in this species and may be a more widely occurring phenomenon in fish with differentiated sex chromosomes than was initially thought.

Chromosome Evolution in African Cichlid Fish: Contributions from the Physical Mapping of Repeated DNAs

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Chromosome evolution in three Brazilian Leptodactylus species (Anura, Leptodactylidae), with phylogenetic considerations

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Comparative karyotype analysis and chromosome evolution in the genus Aplastodiscus (Cophomantini, Hylinae, Hylidae)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Chromosome evolution in the erythrinid fish, Erythrinus erythrinus (Teleostei : Characiformes)

The genus Erythrinus belongs to the family Erythrinidae, a neotropical fish group. This genus contains only two described species, Erythrinus erythrinus being the most widely distributed in South America. Six samples of this species from five distinct Brazilian localities and one from Argentina were studied cytogenetically. Four groups were identified on the basis of their chromosomal features. Group A comprises three samples, all with 2n = 54 chromosomes, a very similar karyotypic structure, and the absence of chromosome differentiation between males and females. One sample bears up to four supernumerary microchromosomes, which look like 'double minute chromosomes' in appearance. Groups B - D comprise the three remaining samples, all sharing an X1X1X2X2/X1X2Y sex chromosome system. Group B shows 2n = 54/53 chromosomes in females and males, respectively, and also shows up to three supernumerary microchromosomes. Groups C and D show 2n = 52/51 chromosomes in females and males, respectively, but differ in the number of metacentric, subtelocentric, and acrocentric chromosomes. In these three groups ( B - D), the Y is a metacentric chromosome clearly identified as the largest in the complement. The present results offer clear evidence that local samples of E. erythrinus retain exclusive and fixed chromosomal features, indicating that this species may represent a species complex.

A cytogenetic study of Diplomystes mesembrinus (Teleostei, Siluriformes, Diplomystidae) with a discussion of chromosome evolution in siluriforms

The mitotic chromosomes, nucleolus organizer regions (NORs), C-banding pattern and nuclear DNA content of Diplomystes mesembrinus were studied. The karyotype, with 2n=56 chromosomes (22m+24sm+6st+4a), has a high chromosome arm number (NF = 102), one chromosome pair with NORs, and a very small amount of heterochromatin. The NOR-bearing arm is entirely heterochromatic and exhibits a marked size polymorphism. The diploid DNA content detected in erythrocyte nuclei of D. mesembrinus was 2.57 ± 0.15 pg/nucleus. The chromosome evolution in Siluriformes is discussed on the basis of available cytogenetic data and it is proposed that 2n=56 is synapomorphic for the order.

Comparative cytogenetics of nine species of Hypoptopomatinae (Teleostei: Siluriformes: Loricariidae): The importance of structural rearrangements in chromosome evolution

Fishes of the subfamily Hypoptopomatinae are very common and found in the lowlands of cis-Andean South America from Venezuela to the north of Argentina. With the main objective of contributing for a better understanding of the importance of chromosome rearrangements in the loricariid evolution, cytogenetic analyses were conducted in nine species of Hypoptopomatinae. The results showed a marked gross karyotypic conservation with the presence of 2n=54 chromosomes in all species analyzed. The main differences were found in the karyotypic formulae level. Most species had a single interstitial Ag-NORs, however terminal Ag-NORs were observed in three species. One species exhibited two Ag-NOR-bearing chromosome pairs. The distribution of C-band positive segments was species specific but chromosome markers were observed among the species analyzed. The gross cytogenetic characteristics observed among the Hypoptopomatinae species are similar to those observed in other primitive Loricariidae species suggesting that small changes, mainly paracentric and pericentric inversion were the main events in the karyotypic evolution of this fish group.

Chromosome mapping of repetitive sequences in Anostomidae species: Implications for genomic and sex chromosome evolution

Background: Members of the Anostomidae family provide an interesting model system for the study of the influence of repetitive elements on genome composition, mainly because they possess numerous heterochromatic segments and a peculiar system of female heterogamety that is restricted to a few species of the Leporinus genus. The aim of this study was to isolate and identify important new repetitive DNA elements in Anostomidae through restriction enzyme digestion, followed by cloning, characterisation and chromosome mapping of this fragment. To identify repetitive elements in other Leporinus species and expand on studies of repetitive elements in Anostomidae, hybridisation experiments were also performed using previously described probes of LeSpeI repetitive elements. Results: The 628-base pair (bp) LeSpeII fragment was hybridised to metaphase cells of L. elongatus individuals as well as those of L. macrocephalus, L. obtusidens, L. striatus, L. lacustris, L. friderici, Schizodon borellii and S. isognathus. In L. elongatus, both male and female cells contained small clusters of LeSpeII repetitive elements dispersed on all of the chromosomes, with enrichment near most of the terminal portions of the chromosomes. In the female sex chromosomes of L. elongatus (Z2,Z2/W1W 2), however, this repeated element was absent. In the remaining species, a dispersed pattern of hybridisation was observed on all chromosomes irrespective of whether or not they were sex chromosomes. The repetitive element LeSpeI produced positive hybridisations signals only in L. elongatus, L. macrocephalus and L. obtusidens, i.e., species with differentiated sex chromosomes. In the remaining species, the LeSpeI element did not produce hybridisation signals. Conclusions: Results are discussed in terms of the effects of repetitive sequences on the differentiation of the Anostomidae genome, especially with respect to sex chromosome evolution. LeSpeII showed hybridisation patterns typical of Long Interspersed Elements (LINEs). The differential distribution of this element may be linked to sex chromosome differentiation in L. elongatus species. The relationship between sex chromosome specificity and the LeSpeI element is confirmed in the species L. elongatus, L. macrocephalus and L. obtusidens. © 2012 da Silva et al.; licensee BioMed Central Ltd.

Chromosome Evolution in Dendropsophini (Amphibia, Anura, Hylinae)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Chromosome evolution in fishes: a new challenging proposal from Neotropical species

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Chromosome evolution in lycosoid spiders (Araneomorphae): a scenario based on analysis of seven species of the families Lycosidae, Senoculidae and Trechaleidae

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Chromosome differentiation patterns during cichlid fish evolution

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)