Abstract The squirrelfish family (Holocentridae) represents a ubiquitous and ecologically vital component of coral reef fauna. Their vast oceanic distribution across oceanic barriers in some species presents a unique opportunity to investigate karyotypic evolution on a vast spatial dimension. Here we conducted the first interpopulational cytogenetic analysis of Myripristis jacobus and Holocentrus adscensionis (Atlantic Ocean), and Sargocentron rubrum (Indian Ocean). Our approach integrates conventional cytogenetic techniques with fluorescence in situ hybridization (FISH) to provide a comprehensive view of their karyotypic structures. Sargocentron rubrum and M. jacobus presented 2n = 48 acrocentric chromosomes, while H. adscensionis exhibited 2n = 50 (2 m + 6sm + 16st + 26a, FN = 74). The 18S ribosomal DNA (18S rDNA)/nucleolar organizer regions stained with silver (Ag-NORs) sites were in a one chromosome pair in S. rubrum and M. jacobus , and in two pairs in H. adscensionis . FISH analysis revealed a single 5S rDNA locus per genome across all studied species. Tol2 elements are dispersed throughout the chromosomes, while Rex3 and the (GA) 15 repeats form more conspicuous centromeric clusters. Cytogenetic comparisons among populations of H. adscensionis and M. jacobus did not show geographic variations, condition congruent with the high genetic connectivity reported for these species. The extensive geographic distribution of these species correlates with biological traits and historical contingencies underlying their karyotypic changes. Our findings provide new insights into karyotype evolution and highlight the need for expanded chromosomal studies in this family. This article aligns with SDG 14 (Life Below Water) of the UN Agenda for Sustainable Development Goals.
Fernandes et al. (Sat,) studied this question.