Abstract
The genera Cichlasoma and Gymnogeophagus belong to the subfamily Cichlinae, the only one in Neotropical cichlids. Cichlasoma dimerus, C. paranaense, C. portalegrense, Gymnogeophagus rhabdotus, and G. lacustris were collected at different points in the Paranapanema and Paraguay basins and the Lagoon of Patos hydrographic system. In addition to conventional analysis, CMA3 fluorochrome staining, and FISH with 18S rDNA probe were performed. All species had a diploid number equal to 48, with interand intraspecific differences in karyotype formulae. All species presented a single AgNOR site, except G. rhabdotus and the C. paranaense population of the Paranapanema River, which revealed more than one pair of nucleolar chromosomes. AgNORs were coincident to 18S rDNA and CMA3. Heterochromatin was distributed in the pericentromeric chromosomal regions and coincident with NORs. For the first time, this work shows cytogenetic data for C. portalegrense, G. lacustris, and G. rhabdotus. Although some results reinforce the idea of conservative chromosome evolution of 2n in Cichlinae, interspecific and populational variations observed confirm that chromosomal rearrangements affect the microstructural karyotype diversification in this group of fish.
Highlights
Cichlidae represents the largest and most diverse family among Neotropical Perciformes, with about 1700 fish species (Eschmeyer and Fong, 2018)
AgNORs were located on a pair of chromosomes for all species, except for the population B of C. paranaense and G. rhabdotus, which showed three to four chromosomes bearing these regions (Figures 1 and 2, boxes)
Despite conservation in diploid number, variations were found in the karyotype formulae of C. dimerus and C. paranaense in comparison to previously studied populations (Martins et al, 1995; Feldberg et al, 2003; Roncati et al, 2007; Poletto et al, 2010)
Summary
Cichlidae represents the largest and most diverse family among Neotropical Perciformes, with about 1700 fish species (Eschmeyer and Fong, 2018). Based on morphological and molecular data, Smith et al (2008) proposed that all Neotropical cichlids belong to a single subfamily, Cichlinae, as a monophyletic group. This subfamily is subdivided into seven tribes: Astronotini, Chaetobranchini, Cichlasomatini, Cichlini, Geophagini, Heroini, and Retroculini. The genera Cichlasoma and Gymnogeophagus belong to the Cichlasomatini and Geophagini tribes, respectively (Kullander, 2003). Cichlasoma presents a wide distribution, occurring in almost all Neotropical regions, from Mexico to the South of South America (Rican and Kullander, 2006). Gymnogeophagus has a more restricted distribution, in which the majority of species is endemic to the coastal river drainage of Uruguay and southern Brazil, in the states of Rio Grande do Sul and Santa Catarina, with exception of G. balzanii, which presents a wider distribution (Reis and Malabarba, 1988)
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