Abstract
In the present study, three species of Lutjaninae, Lutjanus analis, L. griseus and L. synagris, were analyzed by conventional Giemsa staining, C-banding and silver staining, to reveal active Nucleolus Organizer Regions (NORs). Fluorescent in situ hybridization (FISH) was also applied to establish the number and location of the ribosomal gene clusters (18S and 5S rRNA genes). Counts of diploid metaphasic cells revealed a diploid modal chromosome complement composed of 48 acrocentric chromosomes in both L. analis and L. griseus. Two cytotypes were observed in L. synagris: cytotype I, with 2n=48 acrocentric chromosomes, found in 19 specimens, and cytotype II, with 46 acrocentric chromosomes and one large metacentric, found in two specimens. The large metacentric, which possibly originated from a Robertsonian rearrangement, was not found to be sex-related. In the three species, constitutive heterochromatin is located in the centromeres of all chromosomes. NORs were detected on the short arms of a single chromosome pair, number 24 in L. analis and number 6 in both cytotypes of L. synagris. In L. griseus, a polymorphism of the NORs number was detected, by both Ag-staining and FISH, as females show a maximum of three NORs, and males a maximum of six NORs. In all species, minor ribosomal genes were found located on a single chromosome pair. The obtained data, along with those previously reported for other five Lutjanidae species, show that a general chromosome homogeneity occurs within the family, but that derived karyotypes based on Robertsonian rearrangements as well as multiple and variable NORs sites can also be found.
Highlights
The Lutjanidae is a group composed of 17 genera and 105 species of mostly reef-associated marine fishes, which are distributed in all the tropical and subtropical seas of the world (Nelson, 2006)
The obtained data, along with those previously reported for other five Lutjanidae species, show that a general chromosome homogeneity occurs within the family, but that derived karyotypes based on Robertsonian rearrangements as well as multiple and variable Nucleolus Organizer Regions (NORs) sites can be found
The counts of diploid metaphasic cells (Table 1) revealed a modal chromosome complement composed of 2n=48 acrocentric chromosomes (NF=48) in both L. analis and L. griseus and in 19 out of the 21 examined specimens of L. synagris
Summary
The Lutjanidae (snappers) is a group composed of 17 genera and 105 species of mostly reef-associated marine fishes, which are distributed in all the tropical and subtropical seas of the world (Nelson, 2006). Three smaller subfamilies include the Paradichthyinae, with two monotypic genera (Symphorus and Symphorichthys), the Etelinae, with five genera (Aphareus, Aprion, Etelis, Pristipomoides and Rhandallichthys) and 19 species, and the Apsilinae, with four genera (Apsilus, Lipocheilus, Paracesio and Parapristipomoides) and 12 species (Nelson, 2006). In Venezuela, Cervigón (1993) recognizes six genera of Lutjanidae (Etelis, Pristipomoides, Apsilus, Ocyurus, Rhomboplites and Lutjanus ) including 15 species, 10 of which belong to the genus Lutjanus (L. analis, L. apodus, L. aya, L. bucanella, L. cyanopterus, L. griseus, L. jocu, L. mahogoni, L. purpureus, L. synagris and L. vivanus). In spite of their high number and their ecological and economic importance, cytogenetic studies on Lutjanidae are scarce. Only the chromosome number and morphology have been reported and there is no data regarding the chromosomal distribution and composition of the constitutive heterochromatin or numbers and locations of the major and minor ribosomal genes, which have proved to be useful markers in the investigation of the phylogenetic relationships among fish species within a family (Sola et al, 2007)
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