Cytogenetic studies of two freshwater sciaenids of the genus Plagioscion (Perciformes, Sciaenidae) from the central Amazon

Abstract

Cytogenetic characterization of two freshwater sciaenid species from the genus Plagioscion (P. squamosissimus and Plagioscion sp.) was obtained for the first time. Giemsa staining, Ag-NOR and C-banding revealed that both species presented 2n = 48 chromosomes (almost all acrocentric). Single NORs and heterochromatin were found mainly at the pericentromeric position. Karyotypic formulae and NOR location proved to be valuable in showing both interspecific and intraspecific differences. All chromosomes were acrocentric in P. squamosissimus. NORs were located at proximal positions on the long arms of the last chromosome pair of the complement, and were heteromorphic due to size differences. Such heteromorphic NORs seem to be associated with each population sampled. Plagioscion sp. presented two cytotypes: cytotype a (2M + 46A) and cytotype b (48A). In both cytotypes, NOR-bearing chromosomes were located at the proximal position on the long arms of the first chromosome pair of the complement. However, NOR-bearing chromosomes were metacentric in cytotype a and acrocentric in cytotype b.

Cytogenetic studies in Brazilian marine Sciaenidae and Sparidae fishes (Perciformes)

“…In general, the distribution of heterochromatic segments at the centromeric and pericentromeric position identified in Atlantic scianids follows the pattern previously reported in other species of this family (Reggi et al, 1986;Feldberg et al, 1999). A similar heterochromatin distribution pattern was also observed in the sparid A. probatocephalus.…”

“…A single NOR in the pericentromeric region has been considered a basal condition within Perciformes (Affonso et al, 2001), and they are widespread within Scianidae. However, the NOR-bearing chromosome pair can differ among species, such as in Plagioscion sp (1st pair) and P. squamosissimus (24th pair) (Feldberg et al, 1999) or in M. americanus (1st pair), P. acuminatus (2nd pair) and O. punctatissimus (10th pair), presently studied.…”

“…The latter is characterized by a chromosomal variation determined by fissions, with cytotypes varying from 2n = 48 to 52 chromosomes (Gregory et al, 1980). Moreover, a few species may show variation in the number of chromosome arms related to pericentric inversions during karyotypic evolution (Takai and Ojima, 1987;Feldberg et al, 1999). However, this variation seems to be insignificant when compared to other Perciformes families, such as Nototheniidae (2n = 22-58; FN = 44-88) or Bathydraconidae (2n = 20-48; FN = 40-58) (Pisano and Ozouf-Costaz, 2000).…”

“…However, even freshwater Scianidae species, such as Plagioscion squamosissimus and Plagioscion sp, inhabiting inland waters and, therefore, more propitious to karyotypic diversification by the presence of more effective geographic barriers, share a similar karyotype structure (2n = 48 acrocentric) also found in their related marine representatives (Feldberg et al, 1999). These data, coupled with the present results, reinforce that, besides environmental partitions, whether related to physical or biological features, there should be an intrinsic condition for the maintenance of stable karyotypes in some groups.…”

“…So far, karyotypes are reported for 29 of the total number of Scianidae species (Froese and Pauly, 2007), such as, for instance, the 11 marine species analyzed by LeGrand and Fitzsimons (1988), two South American species (Gomes et al, 1983a,b;Pereira et al, 1988), and three Indian species as well (Chakraborty, 1986;Tripathy and Das, 1988), among others. Most scianids have a diploid number of 2n = 48 chromosomes, nearly all acrocentric (Feldberg et al, 1999).…”