Abstract
BACKGROUND: The order Suliformes exhibits significant karyotype diversity, with Sula species showing a Z(1)Z(1)Z(2)Z(2)/Z(1)Z(2)W multiple-sex chromosome system, an uncommon occurrence in avians. Satellite DNAs (satDNAs), which consist of tandemly repeated sequences, often vary considerably even among closely related species, making them valuable markers for studying karyotypic evolution, particularly that of sex chromosome evolution. This study aims to characterize and investigate the potential role of these sequences in the karyotypic evolution of the group, with special attention to the sex chromosomes. METHODS: Through characterizing satDNAs in two Suliformes species (Sula leucogaster and Nannopterum brasilianum) using BGISEQ-500 platform and bioinformatics analysis. Their chromosomal distribution was mapped by fluorescence in situ hybridization (FISH) within their own karyotypes and in three additional Suliformes species (S. sula, S. dactylatra, and Fregata magnificens). RESULTS: Five satDNAs were identified in S. leucogaster and eight in N. brasilianum. Within the genus Sula, three species shared specific satDNA sequences, although with different hybridization patterns. In contrast, the satDNAs of N. brasilianum were species-specific. Additionally, the Z chromosome, including Z(2) in Sula species, showed reduced accumulation of repetitive DNAs. CONCLUSIONS: These results suggest that differential accumulation of repetitive sequences may have contributed to the diversification of karyotypes in this group, particularly influencing the structure and differentiation of sex chromosomes.