Extensive Chromosomal Reorganization in Apistogramma Fishes (Cichlidae, Cichlinae) Fits the Complex Evolutionary Diversification of the Genus

Abstract

Neotropical cichlid fishes are one of the most diversified and evolutionarily successful species assemblages. Extremely similar forms and intraspecific polychromatism present challenges for the taxonomy of some of these groups. Several species complexes have a largely unknown origin and unresolved evolutionary processes. Dwarf cichlids of the genus Apistogramma, comprising more than a hundred species, exhibit intricate taxonomic and biogeographic patterns, with both allopatric and sympatric distributions. However, karyotype evolution and the role of chromosomal changes in Apistogramma are still unknown. In the present study, nine South American Apistogramma species were analyzed using conventional cytogenetic methods and the mapping of repetitive DNA sequences [18S rDNA, 5S rDNA, and (TTAGGG)n] by fluorescence in situ hybridization (FISH). Our results showed that Apistogramma has unique cytogenetic characteristics in relation to closely related groups, such as a reduced 2n and a large number of bi-armed chromosomes. Interspecific patterns revealed a scenario of remarkable karyotypic changes, including a reduction of 2n, the occurrence of B-chromosomes and evolutionary dynamic of rDNA tandem repeats. In addition to the well-known pre-zygotic reproductive isolation, the karyotype reorganization in the genus suggests that chromosomal changes could act as postzygotic barriers in areas where Apistogramma congeners overlap.

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

“…This is one of the most widelydistributed species in the Amazon River basins (Kullander and Ferreira 2006), and the commonly introduced into dam resevoirs throughout Brazil (dos Santos et al 2016;Diamante et al 2017). Heterochromatin is known to play important roles in the chromosomal architecture and karyotype organization, such as assisting in chromosomal segregation, nuclear organization and expression of gene regulation, associated with responses to environmental changes (Grewal and Jia 2007;Varriale et al 2008;Bühler 2009;Ribeiro et al 2017;Viana Ferreira et al 2019). This seems to be the case for the different C. monoculus populations analyzed in our study, where individuals from black and acid waters (Negro and Uatumã rivers), white and black mixed waters (confluence of Negro and Solimões rivers), and in the confluence of white and clear waters (confluence of Amazonas and Tapajós rivers), showed intraspecific variability in their heterochromatic patterns, possibly reflecting chromatin adaptation and/or epigenomic responses to changes in the specific environment inhabited by these different populations.…”

Evolutionary dynamics of pre- and postzygotic reproductive isolation in cichlid fishes

“…However, speciation is still incomplete, as changes in environmental conditions can disrupt species assortative mating [18]. As proposed for late stages in sticklebacks [167], completion of the speciation process in cichlids might require the establishment of major intrinsic incompatibilities, such as changes in karyotypes or chromosomal rearrangements, which can already be observed in some cichlid lineages [141][142][143][144]. Because of great variation in the strength of reproductive isolation among different lineages, cichlid fishes might provide powerful contrasts to elucidate further characteristics distinguishing different stages along the speciation continuum associated with different biogeographic settings.…”

“…Such forms of intrinsic incompatibilities have been reported in multiple different cichlid lineages (reviewed in [141]) and probably played a role in allopatric (e.g. Apistogramma spp., [142]), as well as in sympatric settings (e.g. Laetacara cf.…”

River Reorganization Affects Populations of Dwarf Cichlid Species (Apistogramma Genus) in the Lower Negro River, Brazil

“…Endemic fish populations may have become isolated from widely distributed ones through landscape changes (Wise, 2011a,b;Albert et al, 2017), which makes them an ideal subject with which to study speciation related to geologic drivers of landscape change. The dwarf cichlids from the genus Apistogramma have over a hundred described species, which are well known to have either allopatric or sympatric geographic distributions (Kullander and Ferreira, 2005;Römer, 2006;Costa et al, 2019). It is estimated that many Apistogramma species still need to be described and thus species richness is probably underestimated (Estivals et al, 2020).…”