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

Abstract

We present a database containing cytogenetic data of Neotropical actinopterygian fishes from Venezuela obtained in a single laboratory for the first time. The results of this study include 103 species belonging to 74 genera assigned to 45 families and 17 out of the 40 teleost orders. In the group of marine fishes, the modal diploid number was 2n=48 represented in 60% of the studied species, while in the freshwater fish group the modal diploid complement was 2n=54, represented in 21.21 % of the studied species. The average number of chromosomes and the mean FN were statistically higher in freshwater fish than in marine fish. The degree of diversification and karyotype variation was also higher in freshwater fish in contrast to a more conserved cytogenetic pattern in marine fish. In contrast to the assumption according to which 48 acrocentric chromosomes was basal chromosome number in fish, data here presented show that there is an obvious trend towards the reduction of the diploid number of chromosomes from values near 2n=60 with high number of biarmed chromosomes in more basal species to 2n=48 acrocentric elements in more derived Actinopterygii.Se presenta una base de datos que contiene los datos citogenéticos de peces Actinopterigios Neotropicales de Venezuela obtenidos por primera vez en un solo laboratorio. Los resultados de este estudio incluyen 103 especies pertenecientes a 74 géneros de 45 familias contenidas en 17 de los 40 órdenes de teleósteos. En el grupo de peces marinos, el número diploide modal fue 2n=48 representado en 60% de las especies estudiadas, mientras que en el grupo de peces de agua dulce el complemento diploide modal fue 2n=54, representado en el 21,21% de las especies estudiadas. El número de cromosomas y FN promedio fueron estadísticamente superiores en peces dulceacuícolas. El grado de diversificación y variación en el cariotipo también fue mayor en peces de agua dulce en contraste con un patrón citogenético más conservado en peces marinos. En contraposición a la suposición según la cual 48 cromosomas acrocentricos era el número cromosómico basal en los peces, los datos aquí presentados muestran que existe una evidente tendencia hacia la reducción del número de cromosomas desde valores cercanos a 2n=60 con alto número de cromosomas birrámeos en las especies más basales a 2n=48 elementos acrocéntricos en los actinopterigios más derivados.

Chromosomal stasis in distinct families of marine Percomorpharia from South Atlantic

“…Nonetheless, the karyotype macrostructure of this species follows the common trend observed in most Percomorpharia groups (e.g. Haemulidae, Scianidae, Lutjanidae and Serranidae) (Nirchio et al 2014).…”

“…However, detailed studies of karyotype microstructure are scarce for most marine fish species. Thus, microstructural chromosomal changes not affecting the number and morphology of chromosomes could remain undetected, misleading to the apparent chromosomal stability in Perciformes and allies (Nirchio et al 2014). Therefore, chromosomal studies including banding methods and mapping of specific DNA sequences, as carried out in the present study, are particularly important to infer the karyotype structure of Percomorpharia and the evolutionary forces that could determine interspecific variation in spite of the conservativeness of karyotype macrostructure.…”

Molecular Analysis and Chromosome Mapping of Repetitive DNAs in the Green TerrorAndinoacara rivulatus(Cichlidae: Cichlasomatini)

“…A diploid number 2n = 48 is the most common in fishes, 51,54 and it is also the one typically observed in neotropical cichlids. [55][56][57][58] However, many species of this group, despite sharing this chromosome number, differ in the karyotype formula, an evidence that could be explained by intrachromosomal rearrangements like centromeric shifts. As a result of these processes, karyotypic diversity in neotropical cichlids has a higher rate of evolution than that observed in cichlids from Old World.…”

Allopatric chromosomal variation in Nematocharax venustus Weitzman, Menezes & Britski, 1986 (Actinopterygii: Characiformes) based on mapping of repetitive sequences

“…In spite of being the most cytogenetically studied group of Neotropical ichthyofauna (Nirchio et al, 2014), karyotypic data are still absent for many species and genera of Characiformes, such as Nematocharax. The karyotype macrostructure of N. venustus, including the modal diploid number of 2n=50, high number of biarmed chromosomes and a large metacentric pair (1 st pair), is observed in several species of Characidae.…”