Abstract
The African weakly electric elephantfish family Mormyridae comprises 22 genera and almost 230 species. Up-to-date cytogenetic information was available for 17 species representing 14 genera. Here we report chromosome number and morphology in Hyperopisusbebe (Lacepède, 1803) and Pollimyrusisidori (Valenciennes, 1847) collected from the White Nile system in southwestern Ethiopia. Both taxa displayed the diploid chromosome number 2n = 40, but they differed in fundamental numbers: FN = 66 in H.bebe and FN = 72 in P.isidori; previously the same diploid chromosome number 2n = 40 was reported in an undescribed species of Pollimyrus Taverne, 1971 (FN = 42) from the same region. Our results demonstrate that not only pericentric inversions, but fusions also played a substantial role in the evolution of the mormyrid karyotype structure. If the hypothesis that the karyotype structure with 2n = 50–52 and prevalence of the uni-armed chromosomes close to the ancestral condition for the family Mormyridae is correct, the most derived karyotype structures are found in the Mormyrus Linnaeus, 1758 species with 2n = 50 and the highest number of bi-armed elements in their compliments compared to all other mormyrids and in Pollimyrusisidori with the highest number of bi-armed elements among the mormyrids with 2n = 40.
Highlights
The African weakly electric elephantfishes comprise the family Mormyridae including 22 genera and almost 230 species (Eschmeyer et al 2021; Froese and Pauly 2021)
The karyotype structure with 2n = 50–52 and prevalence of the uni-armed elements is rather infrequent among mormyrids but appears in the genera displaying primitive morphology and mainly basal phylogenetic positions (Taverne 1972; Alves-Gomes and Hopkins 1997; Sullivan et al 2000)
Sudanese river basins (Eschmeyer et al 2021; Froese and Pauly 2021). Both Pollimyrus and Hyperopisus never appeared among basal groups in the mormyrid molecular based phylogenies (Alves-Gomes and Hopkins 1997; Sullivan et al 2000; Lavoué et al 2003)
Summary
The African weakly electric elephantfishes comprise the family Mormyridae including 22 genera and almost 230 species (Eschmeyer et al 2021; Froese and Pauly 2021). The karyotype structure with 2n = 50–52 and prevalence of the uni-armed elements is rather infrequent among mormyrids but appears in the genera displaying primitive morphology (mainly, dentition and electrocyte structure) and mainly basal phylogenetic positions (Taverne 1972; Alves-Gomes and Hopkins 1997; Sullivan et al 2000). Sudanese river basins (Eschmeyer et al 2021; Froese and Pauly 2021) Both Pollimyrus and Hyperopisus never appeared among basal groups in the mormyrid molecular based phylogenies (Alves-Gomes and Hopkins 1997; Sullivan et al 2000; Lavoué et al 2003). Based on the obtained and previous results, the two types of karyotype structure most derived from a hypothetical ancestral condition within the family Mormyridae were defined
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