Abstract
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.
Highlights
Loricariidae is the largest family of the Siluriformes, which includes about 1.000 species distributed in the Neotropical region, and comprises fishes vulgarly called as armored catfishes (Fricke et al, 2020)
Ancistrus aguaboensis presented 2n = 50 chromosomes, a karyotype formula arranged in 16m+10sm+4st+20a, fundamental number (FN) = 80 and, without sex chromosome heteromorphism (Fig. 1A)
Ancistrus aguaboensis has its first karyotype description in this study, and 2n = 50 chromosomes suggests a numerical reduction by centric fusion
Summary
Loricariidae is the largest family of the Siluriformes, which includes about 1.000 species distributed in the Neotropical region, and comprises fishes vulgarly called as armored catfishes (Fricke et al, 2020). It consists of six subfamilies: Delturinae, Hypoptopomatinae, Hypostominae, Lithogeninae, Loricariinae and Rhinelepinae (Armbruster, 2004; Reis et al, 2006). Ancistrini remains a clade rich in genera and with a high morphological diversity (Lujan et al, 2015), which presents constant systematic reformulations and with a lot of undescribed species waiting for scientific validation
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