Comparative Cytogenetics Analysis on Five Genera of Thorny Catfish (Siluriformes, Doradidae): Chromosome Review in the Family and Inferences About Chromosomal Evolution Integrated with Phylogenetic Proposals

Abstract

Doradidae has been a target of phylogenetic studies over the last few years, but chromosomal information about the family is still scarce. Therefore, new cytogenetic data are provided herein and they are correlated with phylogenetic proposals to contribute to the knowledge of chromosomal evolution within doradids. Cytogenetic studies were performed on Trachydoras paraguayensis, Anadoras sp. "araguaia," Ossancora eigenmanni, Platydoras armatulus, and Rhinodoras dorbignyi. O. eigenmanni, P. armatulus, and R. dorbignyi had 2n = 58 chromosomes as found for most doradids, but T. paraguayensis and Anadoras sp. "araguaia" had 2n = 56 chromosomes, probably caused by a chromosomal reduction. There is a great maintenance of 2n = 58 verified in doradids, but karyotype formulas are diverse. Moreover, other markers (i.e., nucleolar organizer regions, heterochromatin distribution, and 5S and 18S rDNA) showed a great diversity among the analyzed species. Contrasting the variability in the chromosomal markers with the maintenance of diploid number, it is likely that inversions and translocations played an important role in chromosome differentiation in Doradidae. Herein, we created an integrative discussion linking cytogenetic data to phylogenetic proposals, based on morphological and genetic features, enabling us to identify possible cytogenetic traits, as well as probable chromosomal plesiomorphy and apomorphy of Doradidae species.

Karyotype Evolution of Talking Thorny Catfishes Anadoras (Doradidae, Astrodoradinae): A Process Mediated by Structural Rearrangements and Intense Reorganization of Repetitive DNAs

“…Assuming that the 2n = 58 chromosomes indeed represent the ancestral diploid number for thorny catfishes, our results show that the 2n = 56 described in all Anadoras species would be a derived condition, likely attributed Cytogenet Genome Res 2022;162:64-75 DOI: 10.1159/000523747 to fusion events, as already reported in Trachydoras paraguayensis [Baumgärtner et al, 2016[Baumgärtner et al, , 2018. We believe that this chromosome reduction does not represent the ancestral condition for these 2 taxa, and it is likely to have arisen from independent events.…”

“…Based on this scenario of karyotype homogeneity, Eler et al [2007] and Milhomem et al [2008] proposed a model of chromosome diversification mediated by pericentric inversion events, due to the constancy of 2n = 58 and great variation in karyotype formulas. Recently, this scenario changed drastically, revealing numeric and structural variations in several thorny catfishes, besides supernumerary chromosomes and a unique ZW sexual system [Takagui et al, 2017[Takagui et al, , 2021Baumgärtner et al, 2018]. According to Takagui et al [2021], the ancestral diploid number for the Doradidae family still remains as an open question, but several lines of evidence support the 2n = 58 chromosomes as a plesiomorphic feature in the family and as the likely ancestral karyotype configuration.…”

“…Pericentric inversions have been frequently detected in many groups of fish, especially among the Siluriformes where they are considered the major rearrangements in the karyotype diversification in Loricariichthys [Takagui et al, 2014], Rineloricaria [Venturelli et al, 2021], Trachelyopterus [Santos et al, 2021], Tatia [Lui et al, 2013a], Pimelodus [Girardi et al, 2018], and Trichomycterus [Oliveira et al, 2016]. Among Doradidae, multiple pericentric inversions events associated with heterochromatin movements occurred independently in several clades and played a key role in the diversification of Wertheimerinae [Eler et al, 2007;Takagui et al, 2019] and Doradinae subfamilies, especially in the large species allocated in the nonfimbriated barbels clade [Milhomem et al, 2008;Baumgärtner et al, 2018;Takagui et al, 2021] and in the widespread species T. paraguayensis [Baumgärtner et al, 2016].…”

“…However, a major obstacle in using this type of approach is the lack of cytogenetic data for some groups, or when they are available, they are either fragmented or restricted to certain clades. Thus they are poorly representative in relation to the total diversity of a given group, as seen for instance within Doradidae thorny catfishes [Baumgärtner et al, 2018;Takagui et al, 2019]. This family has upwards of 96 valid species [Fricke and Eschmeyer, 2021] widely distributed along South America, where they are popularly known as armaus, abotoados, rique-rique, serrudo, among others.…”

Karyotypic characterization of Centromochlus schultzi Rössel 1962 (Auchenipteridae, Centromochlinae) from the Xingu River basin: New inferences on chromosomal evolution in Centromochlus

“…However, several groups of Neotropical fish carry these ribosomal genes in synteny, distant or colocalized. Several recent studies in Siluriformes showed the synteny of these genes (e.g., Baumgärtner et al, 2018;Fonseca et al, 2018;Lorscheider et al, 2018;Takagui et al, 2019;Terra et al, 2019), being considered as a plesiomorphic feature in Tricomycteridae and Loricariidae (Ziemniczak et al, 2012), and an ancestral condition in the sister group of Auchenipteridae, the Doradidae family (Baumgärtner et al, 2018;Takagui et al, 2019).…”