Karyotypic evolution in Neotropical freshwater fish

Abstract

The largest freshwater fish fauna of the world is found in the Neotropical region and includes 2500 to 2700 known species [1], and a total number of species that may actually reach 5000 [2]. Until the late seventies not much was known about the cytogenetic characteristics of these fish and the cytogenetic data available about the Neotropical fish fauna was limited to knowledge of the chromosome number of about 252 species, most of them obtained from specimens of unknown geographical origin, as listed by Almeida-Toledo [3]. Cytogenetic studies focusing on the Neotropical fish species have greatly developed within the last twenty years, mainly in Brazil. The number of species already karyotyped has reached 706, belonging to 207 genera and 38 families [4]. These data include not only chromosome number and formulae, but also data about the presence of differentiated sex chromosomes, supernumerary B-chromosomes, and the location of nucleolus organizer regions (NORs). For a growing number of species, restriction banding analysis, in situ localization of rDNA sequences in the chromosomes [5, 6], of satellite DNA probes (obtained from heterochromatic regions either from pericentromeric sequences [7] or from B-chromosomes [8]) or of telomeric sequences and, more recently, immunocytogenetic analyses [9] are being carried out.KeywordsNucleolus Organizer RegionPericentric InversionKaryotypic EvolutionNeotropical FishFemale HeterogametyThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.