Comparative cytogenetic analyses in Ancistrus species (Siluriformes: Loricariidae)

Abstract

Ancistrus is a specious genus of armored catfishes that has been extensively used for cytogenetic studies in the last 17 years. A comparison of the extensive karyotypic plasticity within this genus is presented with new cytogenetic analysis for Ancistrus cf. multispinis and Ancistrus aguaboensis. This study aims to improve our understanding of chromosomal evolution associated with changes in the diploid number (2n) and the dispersion of ribosomal DNAs (rDNAs) within Ancistrus. Ancistrus cf. multispinis and A. aguaboensis exhibit 2n of 52 and 50 chromosomes, respectively. Given that A. cf. multispinis shares a 2n = 52 also found in Pterygoplichthyini, the sister group for Ancistrini, a Robertsonian (Rb) fusion event is proposed for the 2n reduction in A. aguaboensis. 5S rDNAs pseudogenes sites have already been associated with Rb fusion in Ancistrus and our analysis suggests that the 2n reduction in A. aguaboensis was triggered by double strand breaks (DSBs) and chromosomal rearrangements at 5S rDNA sites. The presence of evolutionary breakpoint regions (EBRs) into rDNA cluster is proposed to explain part of the Rb fusion in Ancistrus. Cytogenetic data presented extends the diversity already documented in Ancistrus to further understand the role of chromosomal rearrangements in the diversification of Ancistrini.

Highly Rearranged Karyotypes and Multiple Sex Chromosome Systems in Armored Catfishes from the Genus Harttia (Teleostei, Siluriformes)

“…The Loricariidae family is an outstanding group to investigate chromosomal breaks and rearrangements that gave rise to extremely diverse karyotypes among its representatives [ 39 , 40 , 41 , 42 ]. These fishes are characterized by a sedentary lifestyle, with rare migratory events [ 43 ].…”

Multiple sex chromosomes in teleost fishes from a cytogenetic perspective: state of the art and future challenges

“…Moreover, it has been repeatedly shown that populations of many teleost species and species complexes are polymorphic for sex chromosome systems [31,59,65,70,79,[83][84][85][86][87][88][89]. These observations point to a very recent, ongoing and recurrent formation of multiple sex chromosomes and stress the importance of proper sampling and sample size.…”

“…This is evidenced by a recent report of experimental crosses between a strain of the platyfish Xiphophorus maculatus with XY and the swordtail Xiphophorus helleri with ZW, which led to the translocation of the sex-determining region to an autosome in hybrids [ 145 ]. It is therefore reasonable to hypothesize that interaction between populations differing in their sex chromosome systems [ 31 , 59 , 65 , 70 , 79 , 83 , 85 – 89 ] can give rise to novel sex chromosomes including multiple sex chromosome systems.…”

Cytogenetic Analysis of <b><i>Panaqolus tankei</i></b> Cramer &amp; Sousa, 2016 (Siluriformes, Loricariidae), an Ornamental Fish Endemic to Xingu River, Brazil

“…In addition, Ancistrini species exhibit great differences in terms of number and positions of rDNAs sites. For example, a single chromosome pair carrying 18S rDNA is a characteristic shared by all analyzed Ancistrus Kner, 1854 species [Bueno et al, 2018;Glugoski et al, 2020]. On the other hand, Pety et al [2018] found multiple sites for 18S rDNA in Peckoltia species, another genus of Ancistrini.…”

“…Several cytogenetic studies involving Ancistrini species point to conservation of the diploid number of 2n = 52 chromosomes [Bueno et al, 2018;Pety et al, 2018;Glugoski et al, 2020], but differences in the karyotype formulae suggest inversions as the primary mechanisms of chromosomal evolution in this group [Ayres-Alves et al, 2017;Bueno et al, 2018]. In addition, Ancistrini species exhibit great differences in terms of number and positions of rDNAs sites.…”