Cytogenetic analysis of Baryancistrus xanthellus (Siluriformes: Loricariidae: Ancistrini), an ornamental fish endemic to the Xingu River, Brazil

Abstract

Baryancistrus xanthellus is a species from the Ancistrini tribe known commonly as "amarelinho " or "golden nugget pleco". It is one of the most popular and valued ornamental fishes due to its color pattern. Also, it is an endemic species from the Xingu River occurring from Volta Grande do Xingu, region where the Belo Monte Hydropower Dam is being built, to São Félix do Xingu. The current study aimed to cytogenetically characterize B. xanthellus . Results point to the maintenance of 2n=52, which is considered the most common condition for the tribe, and a single nucleolus organizer region (NOR). Mapping of the 18S rDNA confirmed the NOR sites, and the 5S rDNA was mapped in the interstitial position of a single chromosome pair. The 18S and 5S rDNA located in different pairs constitute an apomorphy in Loricariidae. Large blocks of heterochromatin are present in pairs 1 and 10 and in the regions equivalent to NOR and the 5S rDNA. Data obtained in this study corroborated with the currently accepted phylogenetic hypothesis for the Ancistrini and demonstrate evidence that the genus Baryancistrus occupies a basal position in the tribe.

Hidden Diversity in the Populations of the Armored Catfish Ancistrus Kner, 1854 (Loricariidae, Hypostominae) from the Paraná River Basin Revealed by Molecular and Cytogenetic Data

“…The NOR mapping provided an excellent marker in the present study, being found in a single chromosome pair in each clade, a condition shared with most other Ancistrus species (Medeiros et al, 2016 ). The variation among clades in the NOR-bearing chromosome may be the result of chromosomal rearrangements occurring during chromosomal evolution.…”

“…The position and distribution of the 5S rDNA sites varied considerably among the four clades, as they do in other Ancistrus species, occupying multiple sites in pericentromeric, interstitial, or terminal positions. This variation is considered to be an important reflection of the enormous karyotypic diversity found in the Ancistrus , which is seen as evidence of the apomorphic condition of this group (Medeiros et al, 2016 ). This variability, together with the disjunction of the ribosomal sites caused by rearrangements or mobile genetic elements appears to be a common condition among Neotropical fish species (de Oliveira et al, 2009 ).…”

Cytogenetic data on Ancistrus sp. (Siluriformes, Loricariidae) of the Paraguay River basin (MS) sheds light on intrageneric karyotype diversification

“…From this starting point, there has been an extensive reduction in the diploid number in the genus Ancistrus (54 to 34) due to possible chromosomal fusions, which can be deduced from the inverse relationship between the number of acrocentric and meta-submetacentric chromosomes. This can be seen in the species with reduced diploid numbers (40, 38, 34), which show little or no acrocentric chromosomes (Mariotto et al 2004, 2006, 2009, 2011, de Oliveira et al 2009, Favarato et al 2016, Medeiros et al 2016). However, other rearrangements such as inversions and/or translocations also occurred during the evolution of the karyotype, resulting in the considerable diversity of the fundamental number observed in this genus…”

“…The karyotype data available for Ancistrus indicate a relation between diploid number and chromosome types; species with a 2n=44 or more have a larger number of acrocentric chromosomes, while species with smaller diploid numbers (2n=34 to 42) have few or no acrocentric chromosomes (de Oliveira et al 2009, Medeiros et al 2016). Artoni and Bertollo (2001) proposed that a karyotype of 2n=54 with a predominance of meta-submetacentric pairs was the primitive condition for the family Loricariidae, which was thus far been found in Ancistrus sp.…”

“…A single NOR in an interstitial location has been considered the plesiomorphic condition in Loricariidae (Artoni and Bertollo 2001, Alves et al 2003, de Oliveira et al 2009, Mariotto et al 2009, 2011, Mendes-Neto et al 2011). However, in Ancistrus , the NOR has been observed in a terminal position for most species but, there is also a significant number of species with interstitial NORs (Medeiros et al 2016). The structural diversity of NORs in Ancistrus related to the different types and sizes of chromosomes may be associated with extensive structural rearrangements (fusions, translocations and/or inversions) that occurred during the karyotype diversification of the genus (de Oliveira et al 2009, Mariotto et al 2011).…”