Comparative cytogenetic of six species of Amazonian Peacock bass (Cichla, Cichlinae): intrachromosomal variations and genetic introgression among sympatric species

Abstract

Cytogenetic data for the genus Cichla Bloch et Schneider, 1801 are still very limited, with only four karyotype descriptions to date. The sum of the available cytogenetic information for Cichla species, points to a maintenance of the diploid number of 48 acrocentric chromosomes, considered a typical ancestral feature in cichlids. In the current study, we performed molecular and classical cytogenetic analyses of the karyotype organization of six species of Cichla, the earliest-diverging genus of Neotropical cichlids. We cytogenetically analysed Cichla kelberi Kullander et Ferreira, 2006, Cichla monoculus Agassiz, 1831, Cichla piquiti Kullander et Ferreira, 2006, Cichla temensis Humboldt, 1821, Cichla vazzoleri Kullander et Ferreira, 2006 and Cichla pinima Kullander et Ferreira, 2006, including three individuals that showed mixed morphological characteristics, likely from different species, suggesting they were hybrid individuals. All individuals analysed showed 2n = 48 acrocentric chromosomes, with centromeric heterochromatic blocks on all chromosomes and a terminal heterochromatic region on the q arm of the 2nd pair. Mapping 18S rDNA gave hybridization signals, correlated with the nucleolus organizer regions, on the 2nd pair for all analyzed individuals. However, we found distinct patterns for 5S rDNA: interstitially at the proximal position on 6th pair of four species (C. kelberi, C. pinima, C. piquiti and C. vazzoleri), and on the distal of the 4th pair in two (C. monoculus and C. temensis). Accordingly, we present here new data for the genus and discuss the evolutionary trends in the karyotype of this group of fish. In addition, we provide data that supports the occurrence of hybrid individuals in the Uatumã River region, mainly based on 5S rDNA mapping.

Karyotypic variation of two populations of the small freshwater stingray Potamotrygon wallacei Carvalho, Rosa & Araújo 2016: A classical and molecular approach

“…Our experiments did not show any ITS signals despite the differences in the karyotypic formula, this absence of ITS might be caused by successive losses and degeneration, leading to gradual shortening of the nonfunctional telomeric arrays as seen in other animal groups [49,50,67,68]. However, the differences in the karyotypic formula might indicate that inversions play a key role in the karyotype differentiation of P. wallacei populations.…”

“…fishes [48][49][50], and in all freshwater stingrays species cytogenetically characterized [22,23,29]. The exception is P. wallacei here analyzed, whose chromosomes exhibited terminal blocks on the long arms of pairs 2 and 3, a pattern, although relatively uncommon, already seen in some marine species [45].…”

Reduced genetic diversity and the success of the invasive peacock bass (Cichliformes: Cichlidae)

“…One of the primordial aspects when assessing peacock bass colonization is the taxonomic identity of the invaders, i.e., if there is one dominant species or a group of them. The genus Cichla shows an extensive phenotypic variation, especially related to the color pattern, which can be very confusing for species identification (Reiss et al, 2012;Quadros et al, 2020). The misidentification of several Cichla species introduced in different regions of Brazil was previously reported by Kullander and Ferreira (2006), such as for C. kelberi (Kullander & Ferreira, 2006), which was erroneously identified as C. monoculus Spix & Agassiz, 1831 and C. piquiti (Kullander & Ferreira, 2006), due to the overlapping morphometric characters and similar coloration patterns.…”