@article {671, title = {Phylogenetic reconstruction of African weakly electric fish (Campylomormyrus spp.) is suggestive of ancient introgression events}, journal = {Molecular Phylogenetics and Evolution}, volume = {214}, year = {2026}, month = {Jan-01-2026}, pages = {108452}, abstract = {

The African weakly electric fish genus Campylomormyrus belongs to the species-rich family Mormyridae and comprises 15 described species. Previous species trees that focus on the genus, have included at most ten species. The resulting phylogenies have been used to explain the evolution of the species-specific electrical organ discharge (EOD) and interpreted in the context of sympatric speciation caused by disruptive selection. However, available molecular phylogenies that are focused on the Campylomormyrus genus rely only on a limited number of genetic markers. Here, we used ddRAD sequencing to genotype 65 individuals from twelve Campylomormyrus species and Gnathonemus petersii at more than 8,000 SNPs. We reconstruct a robust species tree that is suggestive of ancient introgression events between different species, which might affect both genetic and trait variability in the genus. Different levels of genetic and EOD diversity in two significant Campylomormyrus clades reveals that i) certain species might be in early stages of their speciation process, ii) that hybridization/introgression occurs in mormyrids and iii) that EOD-related genes could be potential speciation genes. Our genomic approach demonstrates the significance of these findings in understanding the evolution of Campylomormyrus.

}, keywords = {Ancient introgression, Campylomormyrus, ddRAD sequencing, EOD, phylogeny, speciation}, issn = {1055-7903}, doi = {10.1016/j.ympev.2025.108452}, url = {https://doi.org/10.1016/j.ympev.2025.108452}, author = {Canitz, Julia and Kirschbaum, Frank and Vendrami, David L.J. and Mamonekene, Victor and Tiedemann, Ralph} } @article {667, title = {Organization of the stalk system on electrocytes in mormyrid weakly electric fish Campylomormyrus compressirostris}, journal = {Cell and Tissue Research}, year = {2024}, month = {Dec-20-2024}, pages = {1-17}, abstract = {

The adult electric organ in weakly electric mormyrid fish consists of action-potential-generating electrocytes, structurally and functionally modified skeletal muscle cells. The electrocytes have a disc-shaped portion and, on one of its sides, numerous thin processes, termed stalklets. These unite to stalks leading to a single main stalk that carries the innervation site. Here, we describe the 3-dimensional layout of the stalklet/stalk system in adult Campylomormyrus compressirostris by differential interference contrast microscopy and confocal fluorescence microscopy. Using antibodies against Na+/K+-ATPase \α-subunit and plasma membrane Ca2+-ATPase, we show that these ion pumps are differentially distributed over the stalklet/stalk system, with plasma membrane Ca2+-ATPase being enriched on the stalklet membrane. Stalklets are distributed and organized in a quite uniform pattern on the posterior face of the electrocyte disc and fuse to terminal stalks. The latter then unite in a mostly dichotomic mode to stalks of increasing thickness, with the main stalk measuring about 100\ \µm in diameter. We further analyse the structural organization of stalklets and stalks, with a characteristic cytoskeletal system of bundled actin filaments in the centre and nuclei in subsurface position. These results suggest that the stalklet/stalk system is adapted in its structural layout to generate an action potential highly synchronized over the entire disc-portion of the electrocyte, accounting for the short electric organ discharge in this species. Our results suggest that actin-related proteins overexpressed in electrocytes, as shown previously by transcriptome analysis, may be involved in the organization of the unique F-actin system in stalklets and stalks.

}, keywords = {Ca2+-ATPase, Confocal microscopy, electrocyte, F-actin, Plasma membrane, Sodium pump}, issn = {0302-766X, 1432-0878}, doi = {10.1007/s00441-024-03938-y}, url = {https://doi.org/10.1007/s00441-024-03938-y}, author = {Baumann, Otto and Cheng, Feng and Kirschbaum, Frank and Tiedemann, Ralph} }