Discriminatory profile of rDNA sites and trend for acrocentric chromosome formation in the genus Trachinotus Lacépède, 1801 (Perciformes, Carangidae)
Chromosomal traits have provided valuable information for phylogeny and taxonomy of several fish groups. Three Atlantic Carangidae species of the genus Trachinotus Lacépède, 1801 (T. goodei Jordan et Evermann, 1896, T. carolinus (Linnaeus, 1766) and T. falcatus (Linnaeus, 1758)) were investigated,2n=48 chromosomes but different chromosomal arms (FN number), i.e., 52, 56 and 58, respectively, in view of the different number of two-armed chromosomes found in their karyotypes. Thus, T. goodei, T. carolinus and T. falcatus present a progressive distance from the probable basal karyotype proposed for Perciformes (2n=48 acrocentrics, FN=48). At first sight, these findings do not agree with the phylogenetic hypothesis based on mitochondrial sequences, where T. goodei appear as the most derived species, followed by T. falcatus and T. carolinus, respectively. However, the chromosomal mapping of ribosomal DNAs was informative for clarifying this apparent conflict. Indeed, the multiple 5S and 18S rDNA sites found in T. goodei corroborate the most derived condition for this species. In this sense, the occurrence of the unexpected number of two-armed chromosomes and FN value for this species, as well as for T. carolinus, must be due to additional rounds of acrocentric formation in these species, modifying the macrostructure of their karyotypes.
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