Three sympatric karyomorphs in the fish Astyanax fasciatus (Teleostei, Characidae) do not seem to hybridize in natural populations

Maressa Ferreira-Neto,Mohammed Bakkali,Juan Camacho,Orlando Moreira Filho,Claudio Oliveira,Marcelo Vicari,Roberto Artoni,Fausto Foresti

doi:10.3897/compcytogen.v6i1.2151

Maressa Ferreira-Neto, Mohammed Bakkali + Show 6 more

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https://doi.org/10.3897/compcytogen.v6i1.2151

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Abstract

Ninety individuals of the characid fish Astyanax fasciatus (Cuvier, 1819) were collected at Água da Madalena stream (Botucatu, São Paulo, Brazil) and analyzed for diploid chromosome number 2n and karyotype composition as well as for the chromosomal location of the 5S and 18S ribosomal DNA (rDNA). Whereas no chromosome differences were associated with sex, three different karyomorphs with diploid chromosome numbers 2n=46, 2n=48 and 2n=50 were found. No intermediate 2n numbers were discovered. The 2n=50 karyomorph showed some differences in 18S rDNA location compared to the two other karyomorphs. Finally, all specimens with the 2n=46 karyomorph showed the presence of a partly heterochromatic macro supernumerary chromosome, which was absent in all individuals with the two other karyomorphs. All these results suggest that indviduals of the three different karyomorphs are not likely to hybridize in the examined populations. Our findings strongly suggest the presence of three separate species (sensu biological species concept) easily diagnosed on the basis of differences in the diploid chromosome numbers and other chromosomal markers.

Highlights

The genus Astyanax (Baird et Girard, 1854) is one of the most diversified among Neotropical characid fishes
The cytogenetic analysis of the 90 specimens of Astyanax fasciatus revealed the presence of three different karyomorphs in the sample, showing 2n=46, 2n=48 and 2n=50 chromosomes (Table 2 and Fig. 2 a, c and e, respectively), and with fundamental numbers (NF= number of chromosome arms) equal to 84, 86 and 90, respectively
Sympatry and syntopy for several cytotypes have been reported in Astyanax species, such as A. scabripinnis (Souza and Moreira-Filho 1995) and A. fasciatus (Pazza et al 2006, 2008)

Summary

Introduction

The genus Astyanax (Baird et Girard, 1854) is one of the most diversified among Neotropical characid fishes. Other cases were reported in the Neotropical fish Corydoras aeneus Gill, 1858 (Turner et al 1992), Hoplias malabaricus, Bloch 1794 (Bertollo et al 1997), and Gymnotus carapo Linnaeus, 1758 (Milhomem et al 2008). Astyanax fasciatus is another species that seems to form a “species complex” since the available information points towards the existence of several karyomorphs with the diploid chromosome numbers 2n=45, 2n=46, 2n=47, 2n=48 and 2n=50 (Table 1). The karyotype most frequently cited in the literature is 2n=48 (Table 1), but the known geographical range is larger for the karyomorphs 2n=50 and 2n=46 (Figure 1)

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