Diversidade cromossômica em população do gênero Geophagus (Cichiliformes, Cichlidae): análise citogenética de Geophagus parnaibae (Staeck; Schindler, 2006) da Lagoa Prata, Piauí

Abstract

Cichlids comprise a diverse array of genera, among which Geophagus stands out, currently encompassing 31 described species. One of these, Geophagus parnaibae, is endemic to the Parnaíba River basin and is commonly known as "cará salema." This species occurs in Lagoa da Prata, a marginal waterbody fed by the Parnaíba River and located in the municipality of Parnaíba, Piauí State (Brazil). Previous cytogenetic studies have focused on C-banding, nucleolus organizer regions (NORs), and karyotypic analysis in various species of the genus, with Geophagus brasiliensis being the most extensively investigated. The diploid number in the family Cichlidae ranges from 2n = 46 to 48, with approximately 60% of species exhibiting 2n = 48, indicating a high degree of chromosomal conservation. Nonetheless, cytogenetic data for G. parnaibae remain scarce. In the present study, The direct preparation techniques were employed to obtain mitotic chromosomes in order to determine the diploid number and characterize genomic organization. Silver nitrate staining was used to identify NORs, while C-banding enabled visualization of constitutive heterochromatin. The results revealed a conserved diploid number of 2n = 48; however, the species exhibited a structurally distinct karyotype, multiple NORs, and prominent centromeric heterochromatin. These features distinguish G. parnaibae from closely related species such as G. brasiliensis, suggesting potential chromosomal rearrangements, population isolation, and local adaptations. The observed variability points to ongoing microevolutionary processes, highlighting the importance of cytogenetic studies in geographically isolated populations. Furthermore, the findings underscore the need for complementary analyses using molecular markers and samples from different localities within the Parnaíba River basin to better elucidate the evolutionary mechanisms shaping chromosomal diversity within the genus Geophagus.