Subterranean Fishes of the World

3207

2013

AIm 2013

The genus Astyanax has more than 100 species distributed throughout the Neotropical region. Certain denominations comprise groups of species that gradually are undergoing taxonomic revisions. The main evidence for these species complexes are due to cytogenetic studies, morphological and, more recently, molecular markers and sequencing of mitochondrial DNA. The diploid numbers in Astyanax ranging from 36 to 50 chromosomes, with great numerical and structural variation. Aiming to understand the natural history of this group, the ATPase 6/8 region of the mitochondrial DNA of 18 nominal species were sequenced. Due to the morphological and chromosomal diversity of the group, different cytotypes/populations of some of these nominal species or species complexes were sequenced, totaling approximately 180 individuals. The sequences with 650pb were aligned and a Maximum Likelihood tree based on 500 bootstrap replicates according to the test of evolutionary models (TN93 + G) was constructed. The obtained tree rebuilt three major clades, encompassing 28 evolutionary units. The first one is formed by species belonging to the coastal rivers of Brazil, whose morphological characters includes elongated body and hyaline fins. Among the four nominal species, it is suggested there are seven independent evolutionary units. The chromosomal plesiomorphies that support the group are 2n = 50, with a prevalence of acrocentrics, absence of As51 satellite DNA sites; six to 10 5S rDNA sites distributed in acrocentric chromosomes. The second clade is formed by A. mexicanus and the species possessing oval humeral spot. All of them have 2n = 50 and predominance of submetacentric chromosomes; presence of As51 satellite DNA in few sites; A. mexicanus has six 5S rDNA sites, including a pericentromeric site at a submetacentric pair, that is a marker, meanwhile the other group have a pair of 5S rDNA, just this marker. The third clade is formed by complexes of species A. scabripinnis and A. fasciatus, among others. It is characterized by high chromosome variability with Robertsonian rearrangements, causing several decreases in chromosome number; loss and gain of As51 satellite DNA sites; maintenance of chromosome submetacentric marker with the 5S rDNA site, usually with four sites; in general, few acrocentric chromosomes. Previous work from our group has demonstrated the occurrence of three major clades, which have been strengthened with the addition of further species to the analysis. Despite representing only about 15% of the nominal species, and only one region of mitogenome, the simplesiomorphies observed in morphological and cytogenetic level reinforce the reconstruction obtained by the present analysis and demonstrate its phylogenetic signal in the genus Astyanax. Financial support: CNPq, FAPEMIG.

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