Divergent Chromosome Evolution in Hypostominae Tribes (Siluriformes: Loricariidae): Correlation of Chromosomal Data with Morphological and Molecular Phylogenies

Abstract

Hypostominae is the largest subfamily of Loricariidae, and is widely distributed throughout the Neotropic. In the present article, we analyze three Loricariidae species that were considered part of Hypostominae, from three different tribes, to discuss chromosome evolution in this fish group and to review the existent data for the subfamily. Rhinelepis aspera had 54 chromosomes (20m + 26sm+8st), whereas Pterygoplichthys ambrosettii and Megalancistrus parananus had 52 chromosomes, with 16m+24sm+8st+4a and 18m+24sm+10st, respectively. The karyological data were compared with existent phylogenetic hypotheses, indicating a common ancestor with 2n = 52 chromosomes for the Acanthicus, Hemiancistrus, and Peckoltia clades, as well as for Hypostomini. Shared recurrent characteristics of the tribes are discussed, as well as peculiarities of genera Ancistrus and Hypostomus. We propose that the occurrence of fragile sites demonstrated for Ancistrus facilitated chromosomal rearrangements that decreased the proportion of metacentric/submetacentric chromosomes and the diploid number in many species from this genus. Although Hypostominae is usually considered a subfamily with derived chromosome features, our revision shows that this is valid only for Hypostomini and Ancistrini, which have a divergent chromosome evolution from other tribes that seems to conserve plesiomorphic features.

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.…”

Comparative Cytogenetics Among Three Sympatric Hypostomus Species (Siluriformes: Loricariidae): An Evolutionary Analysis in a High Endemic Region

“…Several cytogenetic studies in Hypostomus revealed a great complexity and diversity of information [10][11][12][13][14][15][16][17][18][40][41][42][43][44][45][46] , showing extensive karyotype variation in this group. Cytogenetic analysis evidenced 2n = 54 chromosomes as an ancestral characteristic in Loricariidae, since it was reported in the basal genera and in the sister group Trichomycteridae 47 .…”

“…Cytogenetic analysis evidenced 2n = 54 chromosomes as an ancestral characteristic in Loricariidae, since it was reported in the basal genera and in the sister group Trichomycteridae 47 . Karyotype analyses in Hypostomus have allowed well-defined evolutionary trends, as the occurrence of high variation in the 2n, due to chromosomal rearrangements, like centric fissions [12][13][14][15][16][17][18][19][20][40][41][42][43][44][45][46] , which could explain the increased 2n present in the H. commersoni (2n = 68 chromosomes), H. derbyi (2n = 68 chromosomes) and H. myersi (2n = 74 chromosomes). Chromosome variability in Hypostomus may be assessed by intraspecific variation of 2n, karyotype formula, heterochromatin localization, and number and localization of NORs sites 15,17,44 .…”

“…The genus Hypostomus Lacépède, 1803 contains the greatest number of species in the Hypostominae subfamily (29 genera in total) 1,[7][8][9] , occurring in various freshwaters ecosystems throughout tropical and subtropical regions in South America 1 . Hypostomus possesses apomorphic morphological and cytogenetic characters among loricariids 10 , such as broad diploid number (2n) ranging (64 to 84 chromosomes) and, usually, multiple sites of rDNAs [11][12][13][14] , while some species have chromosomal characteristics considered to be plesiomorphic in the family, like sinteny in ribosomal genes families 10 . In Hypostomus, karyotype formulae, heterochromatin distribution, and number and localization of rDNAs sites are considered important evolutionary chromosome markers 10,[15][16][17][18] .…”