Karyotype differentiation in Chromaphyosemion killifishes (Cyprinodontiformes, Nothobranchiidae): patterns, mechanisms, and evolutionary implications

Abstract

Chromaphyosemion killifishes are a karyotypically highly diverse group of small, sexually dimorphic fishes living in rainforest rivulets in tropical West and Central Africa. In the present study, we used various chromosome banding and staining techniques to analyse the karyotypes of 13 populations representing seven described species (Chromaphyosemion loennbergii, Chromaphyosemion punctulatum, Chromaphyosemion splendopleure, Chromaphyosemion volcanum, Chromaphyosemion malumbresi, Chromaphyosemion melanogaster, Chromaphyosemion bitaeniatum) and two undescribed forms (Chromaphyosemion cf. lugens, Chromaphyosemion sp. Rio Muni GEMHS00/41). Diploid chromosome numbers (2n) and the number of chromosome arms (NF) ranged from 2n = 24 in C. malumbresi to 2n = 40 in C. bitaeniatum and from NF = 40 in C. volcanum and C. cf. lugens to NF = 54 in one population of C. loennbergii. A tentative XX/XY sex chromosome system was revealed in C. loennbergii, C. melanogaster, C. malumbresi, and Chromaphyosemion sp. Rio Muni GEMHS00/41. Mapping cytogenetic data for all described Chromaphyosemion species onto a recently published mitochondrial DNA phylogeny revealed a complex pattern of chromosomal evolution with several independent reductions of 2n and independent modifications of NF and nucleolus organizer region phenotypes. Together with the results of preliminary crossing and mate choice experiments, the cytogenetic and molecular phylogenetic data suggest that, contrary to previous hypotheses, chromosomal rearrangements are probably not the most important and certainly not the only factor driving speciation in Chromaphyosemion killifishes.

Comparative cytogenetics of Neotropical cichlid fishes (Nannacara, Ivanacara and Cleithracara) indicates evolutionary reduction of diploid chromosome numbers

“…The third evolutionary trend - also called Karyotype “B” in Thompson (1979) – is represented by the opposite evolutionary scenario - mostly centric fusions played role in evolution from the ancestral karyotype, which lead to reduction of diploid chromosome number accompanied by increasing number of metacentric and submetacentric chromosomes ( Thompson 1979 , Poletto et al 2010 ). This trend of chromosome number reduction seems to be parallel to some other fish groups like it was uncovered in killifishes ( Cyprinodontiformes , Nothobranchiidae ) Völker et al (2008) .…”

Differentiation of sex chromosomes and karyotypic evolution in the eye-lid geckos (Squamata: Gekkota: Eublepharidae), a group with different modes of sex determination

“…Chromosomes were also prepared from regenerating tail tips following the methods of Cattin and Ferreira (1989), as later modified by Völker (2006) with a few necessary modifications for reptiles. The tail tip was removed and subsequently left to regenerate for about 3 weeks.…”

Centric Fusions behind the Karyotype Evolution of Neotropical Nannostomus Pencilfishes (Characiforme, Lebiasinidae): First Insights from a Molecular Cytogenetic Perspective

“…Despite centric fusions not being a dominant type of chromosome rearrangement in teleosts, it seems that such a mechanism might indeed predominate in some lineages [59]. Within Teleostei, similar patterns of karyotype differentiation as those unraveled in Nannostomus have also been reported for African annual killifish genera Nothobranchius [60] and Chromaphyosemion [61,62], Gobiidae [63], Nothothenoidei [64], ophichthid eels (Ophichthidae) [54], Umbridae [65,66], and, in a broader context, also in the paleopolyploid Salmonidae family, where this process is apparently linked to the re-diploidization processes [67].…”