Sequential Steps of Chromosomal Differentiation in Atlantic Surgeonfishes: Evolutionary Inferences

Abstract

Surgeonfishes are a species-rich group and a major biomass on coral reefs. Three species are commonly found throughout South Atlantic, Acanthurus bahianus, A. chirurgus, and A. coeruleus. In this paper, we present the first cytogenetic data of these species, revealing a sequential chromosomal diversification. A. coeruleus was characterized by a relatively conserved karyotype evolved by pericentric inversions of some pairs (2n = 48, 2sm + 4st + 42a). In contrast, the karyotypes of A. bahianus (2n = 36) and A. chirurgus (2n = 34) were highly differentiated by the presence of six large metacentric pairs in A. bahianus (12m + 2sm + 4st + 18a) and A. chirurgus (12m + 2sm + 4st +1 6a) probably derived by chromosomal fusions that corroborate their closer relationship. A discernible in tandem fusion represents an autapomorphic character to A. chirurgus. In spite of macrostructure variation, single nucleolar organizer regions (NORs) on short arms of a subtelocentric pair and similar distribution of C-bands were observed in the three species. Overlapping of chromosomal data with molecular phylogeny indicated pericentric inversions which took place nearly at 19 Ma while centric fusions are as recent as 5 Ma. A physical mapping of coding and noncoding sequences in Acanthurus could clarify the role of additional rearrangements during their chromosomal evolution.

Differential hypomethylation of the repetitive Tol2/Alu-rich sequences in the genome of Bodianus species (Labriformes, Labridae)

“… insularis . The monitoring of ribosomal genes in chromosomes in a phylogenetic perspective makes it possible to identify the sequential patterns of change or synteny maintenance over time ( Affonso et al 2014 ; Fernandes et al 2015 ; Costa et al 2016 ), especially in conserved karyotypes, such as in Bodianus .…”

Atlantic surgeonfishes bear only minor microstructural changes in highly derived karyotypes

“…The karyotypes were arranged as previously defined by Affonso et al (2014) with identification of metacentric (m), submetacentric (sm), subtelocentric (st), and acrocentric (a) chromosomes based on arm ratio. An idiogram was built based on the structural features of chromosomal pairs of each species combining the results of mapped sequences.…”

Inferring Diversity and Evolution in Fish by Means of Integrative Molecular Cytogenetics

“…However, the physical mapping of these sequences by FISH in rare situations has revealed a massive dispersion in most of the chromosomes of some species. Such situations are observed in families with conservative evolutionary patterns such as Pomacanthidae [ 49 ] as well as in those with more dynamic patterns such as Gobiidae [ 25 ]. In this last family, the species Ctenogobius smaragdus , with 2 n = 48 chromosomes, exhibits 5S hybridization marks in 42 chromosomes of the karyotype ( Figure 3 ), and it suggests that not all these regions are active [ 50 ].…”