Mitotic and Meiotic Behavior of B Chromosomes in Crenicichla lepidota: New Report in the Family Cichlidae

Abstract

B chromosomes are additional genetic elements to the standard complement. They display distinctive features and have been found in 15% of eukaryote species. In this study, we analyzed 4 populations of Crenicichla lepidota from hydrographic system of Laguna dos Patos/RS (Brazil). All specimens showed 2n = 48 with 6m + 42st - a, FN = 54, with a secondary constriction on the first pair of the complement. Among the 18 samples analyzed, 6 individuals belonging to the Gasômetro and Saco da Alemoa populations presented 1-3 small-sized heterochromatic B chromosomes, with intra- and interindividual variation. Simple AgNORs coincident with 18S rDNA and CMA3 positive/DAPI negative sites were present in all populations. The extra chromosomes did not exhibit any 18S rDNA sites. The meiotic analyses showed heteropycnotic regions in leptotene and zygotene stages, which may be related to the presence of B chromosomes. During pachytene were found 24 bivalents and 1 spatially separated, as well as during metaphases I and diplotene, indicating that there is no association between B chromosomes and those of the A complement. During diakinesis, an unusual meiotic configuration was observed, revealing a proximity between the bivalent and chromosome B (univalent), that might be the result of a heterochromatin affinity between these chromosomes. In anaphase I, late migration of B chromosomes was detected. The low frequency of B chromosomes in the Cichlidae family and in Crenicichla suggests its recent origin in this group and may be ascribable to animal exposure to deleterious effects under certain environmental conditions. Moreover, this is the first report in C. lepidota.

Genomic Characterization of a B Chromosome in Lake Malawi Cichlid Fishes

“…Among cichlid fishes, B chromosomes were first identified in species from South America [35,36]. More recently they have been identified also in species from lakes Victoria and Malawi in East Africa [37,38]. B chromosomes have been found in at least 7 species from Lake Malawi.…”

B chromosome polymorphism in South American cichlid

“…This is the second report for B chromosomes in C. lepidota. The first population discovered with extra chromosomes in some individuals was in the Patos-Mirim basin [23]. Despite the proximity of these populations, around 120 km, they show B chromosomes with different characteristics.…”

“…Despite the proximity of these populations, around 120 km, they show B chromosomes with different characteristics. Pires et al [23] highlighted the occurrence of small-sized heterochromatic extra chromosomes. This B chromosome size is the most frequent type of karyotype component found in Neotropical Cichlidae [32], which is chromosomes was independent in this fish group; this heterochromatin had no role in the origin and evolution of these chromosomes.…”

“…However, B chromosome polymorphisms have been reported for Amazonian populations of C. reticulata (northern Brazil) [24] and for C. lepidota from Patos Lagoon Basin (southern Brazil) [23]. These populations showed intra-and interindividual variation for presence and number of B chromosomes (zero to three B chromosomes) that are entirely heterochromatic (type III and II, respectively, according to Foresti et al [6]).…”

“…Crenicichla lepidota is a South American cichlid distributed in Argentina, Bolivia, Brazil, and Paraguay, along the basins of Paraná River, Paraguay River, Guaporé River, Uruguay River, and along the coast of Rio Grande do Sul (southern Brazilian state) [10]. An invariant diploid number 2n = 48 has been reported for Crenicichla species [11][12][13][14], with C. lepidota being no exception [9,[15][16][17][18][19][20][21][22][23].…”