Evolutionary Tracks of Chromosomal Diversification in Surgeonfishes (Acanthuridae: Acanthurus) Along the World's Biogeographic Domains.

Maria Aparecida Fernandes,Krit Pinthong,Luiz Antônio Carlos Bertollo,Alongklod Tanomtong,Wagner Franco Molina,Allyson Santos De Souza,Clóvis Coutinho Da Motta-Neto,Weerayuth Supiwong,Amanda Tôrres Borges,Gideão Wagner Werneck Félix Da Costa,Marcelo De Bello Cioffi,Rodrigo Xavier Soares

doi:10.3389/fgene.2021.760244

Abstract

Fishes of the genus Acanthurus (Acanthuridae) are strongly related to reef environments, in a broad biogeographic context worldwide. Although their biological aspects are well known, cytogenetic information related to this genus remains incipient. In this study, Acanthurus species from populations inhabiting coastal regions of the Southwest Atlantic (SWA), South Atlantic oceanic islands (Fernando de Noronha Archipelago and Trindade Island), Greater Caribbean (GC), and Indo-Pacific Ocean (the center of the origin of the group) were analyzed to investigate their evolutionary differentiation. For this purpose, we employed conventional cytogenetic procedures and fluorescence in situ hybridization of 18S rDNA, 5S rDNA, and H3 and H2B-H2A histone sequences. The Atlantic species (A. coeruleus, A. chirurgus, and A. bahianus) did not show variations among them, despite their vast continental and insular distribution. In contrast, A. coeruleus from SWA and GC diverged from each other in the number of 18S rDNA sites, a condition likely associated with the barrier created by the outflows of the Amazonas/Orinoco rivers. The geminate species A. tractus had a cytogenetic profile similar to that of A. bahianus. However, the chromosomal macrostructures and the distribution of rDNA and hisDNA sequences revealed moderate to higher rates of diversification when Acanthurus species from recently colonized areas (Atlantic Ocean) were compared to A. triostegus, a representative species from the Indian Ocean. Our cytogenetic data covered all Acanthurus species from the Western Atlantic, tracked phylogenetic diversification throughout the dispersive process of the genus, and highlighted the probable diversifying role of ocean barriers in this process.

Highlights

Acanthuridae represents a charismatic group of primarily large-bodied herbivorous fish species, which play an important ecological role in benthic communities and the resilience of coral environments in all tropical and subtropical seas (Randall, 2001; Green and Bellwood, 2009; Russ et al, 2018)
Acanthurus triostegus from the Andaman Sea, analyzed for the first time has 2n 48 acrocentric chromosomes (FN 48), with AgNOR sites located in the short arm of pair 24
The 18S rDNA sites occur exclusively in the short arm of pair 24 in A. triostegus, the sites are located in the short arms of the largest subtelocentric pair, without interpopulation variability, in A. tractus, A. bahianus, and A. chirurgus

Summary

Introduction

Acanthuridae (surgeonfishes, tangs, and unicornfishes) represents a charismatic group of primarily large-bodied herbivorous fish species, which play an important ecological role in benthic communities and the resilience of coral environments in all tropical and subtropical seas (Randall, 2001; Green and Bellwood, 2009; Russ et al, 2018). The common name “surgeonfish” refers to the peculiar scalpellike modified scales on both sides of the caudal peduncle that is used in inter- and intraspecific aggressive interactions (Randall, 2001). Due to their attractive colors and shapes, surgeonfishes dominate aquarium trade in several areas (Sadovy and Vincent, 2002; Papavlasopoulou et al, 2014). Despite the growing set of genetic data on Acanthuridae, spanning the nuclear (Bernardi et al, 2018) and the mitochondrial (Ludt et al, 2020) genomes, the cytogenetic features of Acanthuridae are still largely incipient (

Methods

Results

Conclusion