Caracterização cromossômica de Psalidodon fasciatus, Cuvier 1819 (Characiformes, Characidae) do município de Santa Helena - PR

Abstract

The Neotropical region has the largest known continental water ichthyofauna, harboring a high biodiversity of species and it is considered a region still poorly understood. In this perspective, broadening the understanding of the chromosomal diversity of the its ichthyofauna becomes a potential tool for the general understanding of biodiversity and, consequently, for the expansion of actions that strengthen models of environmental preservation and adequate management of aquatic systems. The Characidae family is one of the largest and most complex among the families of Characiformes, demonstrating descriptive inconsistencies in their kinship relationships, with frequent monophyletic uncertainties, such as P. fasciatus. Therefore, this study aimed to characterize Psalidodon fasciatus specimens by classical cytogenetic methodologies from a natural population of Santa Helena-PR. Sixteen specimens (6 males and 10 females) of Psalidodon aff. Fasciatus have been colected. Analyzes have been performed using Giemsa staining, C-Banding and silver nitrate impregnation (AgNOR). The most frequent diploid number found in the analyzed specimens was 2n=50 chromosomes (8m+24sm+6st+12a, FN = 88), which was found in 5 males and 8 females. However, in 3 specimens, 2 females and 1 male, a diploid number of 2n=48 chromosomes (8m+24sm+6st+10a, NF=86) was observed. In the 2n=50 karyomorph, markings by heterochromatin blocks associated with the AgNORs were evidenced in the terminal regions of the submetacentric chromosome pairs 8 and 9, while in the 2n=48 karyomorph, some conspicuous markings were observed in the terminal region of the acrocentric chromosome pair 23 and only in one chromosome of the submetacentric pair 7, also in terminal position. The specimens analyzed in the present study, although morphologically identified as Psalidodon aff. fasciatus, showed considerable chromosomal divergences (diploid number, NF, Ag-NORs and C Banding) when compared with each other and with other studied populations, and ca be separated into two distinct karyomorphs. Thus, such chromosomal variation suggests possible reproductive isolation, reinforcing the hypothesis that P. fasciatus is a complex of species.