Cytogenetic analysis in Tetragonopterus franciscoensis (Characiformes): another piece to the karyoevolutionary puzzle of tetra fishes

Tetragonopterus is a taxonomically complex genus in Characidae, being currently represented by nine species according to integrative approaches. One of them, T. franciscoensis was recently validated in rivers from northeastern Brazil. Even though molecular and morphological data have been collected in Tetragonopterus, the cytogenetic analyses in this group are scarce despite of the role of chromosomal variation in speciation. Herein, we present the first detailed karyotypic study in T. franciscoensis along with a comparative analysis with published cytogenetic data in characin fish. All specimens shared 2n=52 distributed in 12 metacentric (m), 12 submetacentric (sm), and 28 subtelocentric/acrocentric (st/a) chromosomes for both sexes as well as single nucleolus organizer regions on short arms of pair 8 and several GC-rich sites. The mapping of telomeric sequences (TTAGGG)n revealed no telomeric interstitial signals. While subtle cytogenetic differences were observed between samples from northeastern basins in Brazil, corroborating a recent genetic divergence, distinct karyotypes were detected in relation to congeneric taxa from other Brazilian regions. Therefore, the origin of large biarmed pairs in species with low 2n values should be related to occurrence of centric fusions.