﻿AbstractThe karyotype differentiation of the twelve known members of theNothobranchiusugandensisWildekamp, 1994 species
group is reviewed and the karyotype composition of seven of its species is described
herein for the first time using a conventional cytogenetic protocol. Changes in the
architecture of eukaryotic genomes often have a major impact on processes underlying
reproductive isolation, adaptation and diversification. African annual killifishes of the
genusNothobranchiusPeters, 1868 (Teleostei:Nothobranchiidae),
which are adapted to an extreme environment of ephemeral wetland pools in African
savannahs, feature extensive karyotype evolution in small, isolated populations and thus
are suitable models for studying the interplay between karyotype change and species
evolution. The present investigation reveals a highly conserved diploid chromosome number
(2n = 36) but a variable number of chromosomal arms (46–64) among members of theN.ugandensisspecies group, implying a
significant role of pericentric inversions and/or other types of centromeric shift in the
karyotype evolution of the group. When superimposed onto a phylogenetic tree based on
molecular analyses of two mitochondrial genes the cytogenetic characteristics did not show
any correlation with the phylogenetic relationships within the lineage. While karyotypes
of many otherNothobranchiusspp. studied to date diversified mainly via chromosome fusions and fissions, theN.ugandensisspecies group maintains
stable 2n and the karyotype differentiation seems to be constrained to intrachromosomal
rearrangements. Possible reasons for this difference in the trajectory of karyotype
differentiation are discussed. While genetic drift seems to be a major factor in the
fixation of chromosome rearrangements inNothobranchius, future studies are
needed to assess the impact of predicted multiple inversions on the genome evolution and
species diversification within theN.ugandensisspecies group.