Karyotype differentiation in <i>Chromaphyosemion</i> killifishes (Cyprinodontiformes, Nothobranchiidae). II: Cytogenetic and mitochondrial DNA analyses demonstrate karyotype differentiation and its evolutionary direction in <i>C. riggenbachi</i>

Abstract

African killifishes of the genus Chromaphyosemion show a high degree of phenotypic and karyotypic diversity. The latter is especially pronounced in C. riggenbachi, a morphologically defined species restricted to a small distribution area in Cameroon. This study presents a detailed reconstruction of karyotype differentiation within C. riggenbachi using conventional Giemsa staining and sequential chromosome banding as well as a phylogenetic analysis based on part of the mitochondrial (mt) cytochrome b gene from eleven populations. The cytogenetic analysis revealed differences in chromosome morphology, banding patterns and/or diploid chromosome number (2n) among all populations examined. Diploid number ranged from 2n = 20 to 2n = 36 and varied mainly among populations, while C-banding patterns and NOR phenotypes showed fixed differences among populations as well as some variability within populations. The mtDNA analysis disclosed five clearly differentiated haplotype groups. Mapping the karyotype data onto the mtDNA dendrogram revealed a decrease in 2n from the most basal to the most derived groups, thus demonstrating a reduction of 2n during their evolutionary history. Our results indicate that karyotype differentiation involved Robertsonian fusions as well as non-Robertsonian processes. Causes of the high karyotypic variability may include an elevated chromosomal mutation rate as well as certain features of the ecology and mating system that could facilitate the fixation of chromosomal rearrangements. The pattern of karyotype and haplotype differentiation and the results of previous crossing experiments suggest incipient speciation in C. riggenbachi.

Paracentric Inversions Differentiate the Conservative Karyotypes in Two <b><i>Centropomus</i></b> Species (Teleostei: Centropomidae)

“…In fact, before fixation, rearrangements are present in a transitory heterozygous state in populations. Similarly, as in some individuals of the killifish Chromaphyosemion riggenbachi [Völker et al, 2006], polymorphism due to a paracentric inversion was also found in C. undecimalis , indicating ongoing chromosomal reorganizations in Centropomus. It is also noteworthy that snooks are protandric hermaphrodites which are born as males and later become females [Taylor et al .…”

“…Since paracentric inversions do not affect the morphology of the chromosomes, a number of markers are required to reveal them. In some cases, these inversions were detected when NORs were involved [Moreira-Filho et al, 1984;Ráb et al, 2002;Cardoso et al, 2013] and, less frequently, by changes in the position of 5S rDNA sites [Kavalco et al, 2004] or GC-rich heterochromatic regions [Völker et al, 2006].…”

Note on the banded karyotype of the enigmatic South Asian loach Vaillantella maassi (Cypriniformes: Vaillantellidae)

“…Noninvasive chromosome preparation was made from regenerating fin tissue according to Völker et al (2006). Sequential CMA 3 -fluorescence banding (Sola et al 1992), Giemsa staining, and AgNO 3 -staining (Howell and Black, 1980) were performed to detect NORs (i.e., major rDNA clusters).…”

Karyotype Patterns ofHypsolebias antenori(Cyprinodontiformes: Rivulidae): An Endangered Killifish of the Semiarid Region of Brazil

“…Unlike other Cyprinodontiformes, H. antenori showed no evidence of AT-rich regions in the karyotype, as hypothesized due to intense structural rearrangements occurring in chromosomes of some species [39]. This condition, associated with the occurrence of two GC-rich regions, coincident with nucleolar organizer regions, suggests lower participation of Robertsonian translocation events, frequent in several species [15, 19, 38–40].…”

“…More recently, extreme evolutionary dynamics involving chromosomal rearrangements has also been identified in annual African fish species of the genus Chromaphyosemion , where substantial cytogenetic changes related to chromosome morphology, besides banding patterns and/or diploid number between analyzed populations, were observed [39]. The karyotypic diversification among populations and species of this genus is strongly modeled by mechanisms of Robertsonian translocation, as well as other complementary processes including heterochromatinization [40].…”