Abstract
Wrasses (Labridae) are extremely diversified marine fishes, whose species exhibit complex interactions with the reef environment. They are widely distributed in the Indian, Pacific and Atlantic oceans. Their species have displayed a number of karyotypic divergent processes, including chromosomal regions with complex structural organization. Current cytogenetic information for this family is phylogenetically and geographically limited and mainly based on conventional cytogenetic techniques. Here, the distribution patterns of heterochromatin, GC-specific chromosome regions and Ag-NORs, and the organization of 18S and 5S rDNA sites of the Atlantic species Thalassoma noronhanum (Boulenger, 1890), Halichoeres poeyi (Steindachner, 1867), Halichoeres radiatus (Linnaeus, 1758), Halichoeres brasiliensis (Bloch, 1791) and Halichoeres penrosei Starks, 1913, belonging to the tribe Julidini were analyzed. All the species exhibited 2n=48 chromosomes with variation in the number of chromosome arms among genera. Thalassoma noronhanum has 2m+46a, while species of the genus Halichoeres Rüppell, 1835 share karyotypes with 48 acrocentric chromosomes. The Halichoeres species exhibit differences in the heterochromatin distribution patterns and in the number and distribution of 18S and 5S rDNA sites. The occurrence of 18S/5S rDNA syntenic arrangements in all the species indicates a functionally stable and adaptive genomic organization. The phylogenetic sharing of this rDNA organization highlights a marked and unusual chromosomal singularity inside the family Labridae.
Highlights
Wrasses (Labridae) are one of the most abundant and ecologically diversified fish groups in tropical reefs (Choat and Bellwood 1998)
The Ag-nucleolus organizer regions (NORs) are positioned on the short arms of the single submetacentric pair of T. noronhanum (Fig. 2a)
In Halichoeres species, these sites are located in two chromosome pairs, except in H. penrosei, where they are located on the short arms of pair 15 (Fig. 2b, highlighted)
Summary
Wrasses (Labridae) are one of the most abundant and ecologically diversified fish groups in tropical reefs (Choat and Bellwood 1998). Their biodiversity is highlighted by nine tribes with 82 genera and 530 species (Westneat and Afaro 2005, Eschmeyer and Fong 2016), which exhibit extensive biological interactions in tropical reefs and temperate regions around the world (Choat and Bellwood 1998, Wainwright et al 2004, Nelson 2006). Cytogenetic analyses in Labridae have revealed particular trends in the karyotypic evolution of their clades (Sena and Molina 2007). The first one is characterized by conserved karyotypes, with 48 acrocentric chromosomes; the second by 48 chromosomes with an increase in the chromosome arms (NF); the third by a reduction in the number of chromosomes (
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