Cytogenetic Diversity and the Evolutionary Dynamics of rDNA Genes and Telomeric Sequences in theAncistrusGenus (Loricariidae: Ancistrini)

Abstract

The Ancistrus genus differs from other Ancistrini due to its wide karyotypic diversity, varied diploid numbers, differences in sex chromosomes, and large number of species, as well as its tendency to form small populations with low vagility. This study investigated the role of 5S and 18S rDNA and telomeric repetitive sequences in the evolution of the karyotypic macrostructure of seven species of the genus Ancistrus from the Central Amazon. The results indicate a strong correlation between the location of ribosomal sites and fragile sites in the genome, particularly of 5S rDNA sequences, which are associated, in some species, with telomeric sequences at the sites of chromosomal healing. Moreover, the occurrence of two lineages was observed with regard to the synteny of ribosomal genes. The species of the genus Ancistrus showed high chromosomal lability associated with breakpoints, which was characterized by the presence of repetitive DNA sequences and this process is suggested to be an evolutionary model for the rapid fixation of structural rearrangements.

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

“…In the Ancistrini so far, only two genera have data on 5S rDNA: Ancistrus (Mariotto et al, 2011;Favarato et al, 2016) and Hypancistrus (Silva et al, 2014). As it has been observed for the 18S rDNA, the 5S rDNA also presented variable forms among the different species of Ancistrini.…”

“…In this tribe, the most frequent diploid number is 52 chromosomes (Table 1). 2, 8, 9, 15, 16, 18, 19, 20, 22, 23, 24, 26 Oliveira et al (2008); Favarato et al (2016) Ancistrus sp. Catalão Cardoso et al (2013) With the exception of Ancistrus, for which the karyotypic differentiation is usually associated to a reduction in the diploid number (Oliveira et al, 2007(Oliveira et al, , 2008(Oliveira et al, , 2009Mariotto et al, 2009), there is a tendency towards maintaining the diploid number in the tribe.…”

“…Studies conducted so far in the group suggest that the localization of the 5S rDNA in a single chromosome pair is less frequent (Table 1), occurring in a few species of Ancistrus (Mariotto et al, 2011;Favarato et al, 2016) and in B. xanthellus. According to Martins & Galetti (1999), the localization of the ribosomal genes in different chromosomes may be advantageous if compared to the syntenic disposition because it might avoid unfavorable arrangements (Dover, 1986), since the occurrence of unequal crossing-over might be frequent in chromosomes with co-located ribosomal genes.…”

Co-located 18S/5S rDNA arrays: an ancient and unusual chromosomal trait in Julidini species (Labridae, Perciformes)

“…On the other hand, heterogeneous and large amounts of repetitive DNAs are related in several families with notable levels of chromosomal rearrangements and differentiation (Moreira-Filho and Bertollo 1991, Souza et al 2001, Favarato et al 2016). Among the repetitive DNAs, rDNA has a major role in karyotype diversification.…”

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

“…de Oliveira et al 2009, Mariotto et al 2011, 2013, Favarato et al 2016). The karyotype data available for this genus indicate considerable chromosomal diversity, with diploid numbers ranging from 2n=34 chromosomes in Ancistrus cuiabae (Mariotto et al 2009) to 2n=54 in Ancistrus claro (Mariotto et al 2011).…”