Cytogenetic markers to understand chromosome diversification and conflicting taxonomic issues in Rineloricaria (Loricariidae: Loricariinae) from Rio Grande do Sul coastal drainages

Chromosomal rearrangements and the first indication of an ♀X1X1X2X2/♂X1X2Y sex chromosome system in Rineloricaria fishes (Teleostei: Siluriformes)

“…Rineloricaria features extensive chromosomal variability reflected in both 2 n (36–70) and karyotype structure, including records of supernumerary (B) chromosomes (Alves et al ., 2003; Takagui et al ., 2020; Venturelli et al ., 2021). In this study, we present the first cytogenetic data for Rineloricaria teffeana , an endemic species from the Amazon.…”

“…Three karyotypic groups have been distinguished in the Loricariinae subfamily: (i) species with 2 n below 48 chromosomes; (ii) species with 2 n = 52–58, a range closer to a considered plesiomorphic karyotype for Loricariinae (Alves et al ., 2003; Artoni & Bertollo, 2001; Blanco et al ., 2017); and (iii) species with 2 n higher than 60 chromosomes (Takagui et al ., 2020). The majority of so‐far karyotyped Rineloricaria species (approximately 70%; see Table 1 in Venturelli et al ., 2021) belong to group III, which covers mostly the species from the coastal region of southern and south‐eastern Brazil. When put into the context of the phylogenetic relationships among Rineloricaria spp.…”

“…(Covain et al ., 2016), the cytogenetic data suggest parallel increases and decreases in 2 n in several lineages but the prevailing trend is towards the increase in 2 n accompanied by the elevated number of monoarmed ( i.e . subtelocentric and acrocentric) chromosomes, which points to an important contribution of centric fissions to chromosomal differentiation of this genus (Venturelli et al ., 2021). R. teffeana , together with R. latirostris , R. lanceolata , belongs to the group of species with 2 n ≤ 48 chromosomes.…”

“…multiple 5S rDNA clusters matches the general trend observed in many other Rineloricaria spp. (Glugoski et al ., 2022; Primo et al ., 2017; Takagui et al ., 2020; Venturelli et al ., 2021). On the other hand, the syntenic organization in the form of adjacent 5S and 18S rDNA sites on the chromosome pair 4 in R. teffeana is exceptional for the genus and, according to recent knowledge, it may serve as a species‐specific marker.…”

“…Cytogenetic studies of Rineloricaria are limited to the chromosomal characterization of 16 species from different river basins in southern and south‐eastern Brazil (reviewed in Venturelli et al ., 2021; Takagui et al ., 2020), representing approximately 23% of the species diversity described for the genus to date. Although the cytogenetic data for Rineloricaria are still sparse, they have already revealed substantial inter‐ and intraspecific variability, where the diploid chromosome number (2 n ) ranges from 36 (in R. latirostris ; Giuliano‐Caetano, 1998) to 70 chromosomes (in R. lima , R. longicauda and R. quadrensis ; Rosa et al ., 2012; Venturelli et al ., 2021). At the intraspecific level, extensive structural polymorphisms have been well documented in Rineloricaria latirostris where the 2 n of different individuals ranges gradually from 36 to 48 chromosomes, suggesting that this taxon is a probable species complex (Giuliano‐Caetano, 1998).…”