Evolução cromossômica na família Callichthyidae (Ostariophysi: Siluriformes) : aumento, conservação ou redução do número diploide?

Abstract

Structure and number changes of chromosomes can provide evidences on the processes involved in the diversification of a group. For fish, although chromosomal diversity is partially known, different hypotheses indicate that the diploid number may have increased, decreased or remained constant throughout evolutionary history. Here, we compiled all cytogenetic data available in the literature for the family Callichthyidae and presented a complete hypothesis about chromossomal evolution in the family. We also provided an original description of the cytogenetic characteristics (diploid number, nucleolus organizing regions and constitutive heterochromatin) of Aspidoras poecilus from the population of the ‘Ribeirão Ínsula – MT’ stream. Our probabilistic analyzes demonstrated that events of fusion, fission, duplication of the entire chromosome set and partial duplications probably occurred during the evolution of the family. The population of A. poecilus has 2n = 46, composed of 24M + 18SM + 4ST, with large heterochromatic blocks in the interstitial and centromeric regions and heteromorphism in the nucleolus organizing regions present in two chromosomes. Althought there is still a gap in cytogenetic data for callictids, our analyses present a quasi-complete picture of chromossomal evolution for the family, and indicate that the structural diversity of chromosomes can present independent patterns in a moderately small vertebrate family, with events of increase, conservation and maintenance present at different taxonomic levels.