@phdthesis{Cheng2024,
  author    = {Cheng, Feng},
  title     = {Evolution and ontogeny of electric organ discharge in African weakly electric fish genus Campylomormyrus: a genomic and transcriptomic perspective},
  doi       = {10.25932/publishup-63017},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-630172},
  school      = {Universit{\"a}t Potsdam},
  pages     = {176},
  year      = {2024},
  abstract  = {The African weakly electric fishes (Mormyridae) exhibit a remarkable adaptive radiation possibly due to their species-specific electric organ discharges (EODs). It is produced by a muscle-derived electric organ that is located in the caudal peduncle. Divergence in EODs acts as a pre-zygotic isolation mechanism to drive species radiations. However, the mechanism behind the EOD diversification are only partially understood. The aim of this study is to explore the genetic basis of EOD diversification from the gene expression level across Campylomormyrus species/hybrids and ontogeny. I firstly produced a high quality genome of the species C. compressirostris as a valuable resource to understand the electric fish evolution. The next study compared the gene expression pattern between electric organs and skeletal muscles in Campylomormyrus species/hybrids with different types of EOD duration. I identified several candidate genes with an electric organ-specific expression, e.g. KCNA7a, KLF5, KCNJ2, SCN4aa, NDRG3, MEF2. The overall genes expression pattern exhibited a significant association with EOD duration in all analyzed species/hybrids. The expression of several candidate genes, e.g. KCNJ2, KLF5, KCNK6 and KCNQ5, possibly contribute to the regulation of EOD duration in Campylomormyrus due to their increasing or decreasing expression. Several potassium channel genes showed differential expression during ontogeny in species and hybrid with EOD alteration, e.g. KCNJ2. I next explored allele specific expression of intragenus hybrids by crossing the duration EOD species C. compressirostris with the medium duration EOD species C. tshokwe and the elongated duration EOD species C. rhynchophorus. The hybrids exhibited global expression dominance of the C. compressirostris allele in the adult skeletal muscle and electric organ, as well as in the juvenile electric organ. Only the gene KCNJ2 showed dominant expression of the allele from C. rhynchophorus, and this was increasingly dominant during ontogeny. It hence supported our hypothesis that KCNJ2 is a key gene of regulating EOD duration. Our results help us to understand, from a genetic perspective, how gene expression effect the EOD diversification in the African weakly electric fish.},
  language  = {en}
}
@phdthesis{Makower2016,
  author    = {Makower, Katharina},
  title     = {The roles of secondary metabolites in microcystis inter-strain interactions},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-93916},
  school      = {Universit{\"a}t Potsdam},
  pages     = {X, 131},
  year      = {2016},
  abstract  = {Among the bloom-forming and potentially harmful cyanobacteria, the genus Microcystis represents a most diverse taxon, on the genomic as well as on morphological and secondary metabolite levels. Microcystis communities are composed of a variety of diversified strains. The focus of this study lies on potential interactions between Microcystis representatives and the roles of secondary metabolites in these interaction processes. The role of secondary metabolites functioning as signaling molecules in the investigated interactions is demonstrated exemplary for the prevalent hepatotoxin microcystin. The extracellular and intracellular roles of microcystin are tested in microarray-based transcriptomic approaches. While an extracellular effect of microcystin on Microcystis transcription is confirmed and connected to a specific gene cluster of another secondary metabolite in this study, the intracellularly occurring microcystin is related with several pathways of the primary metabolism. A clear correlation of a microcystin knockout and the SigE-mediated regulation of carbon metabolism is found. According to the acquired transcriptional data, a model is proposed that postulates the regulating effect of microcystin on transcriptional regulators such as the alternative sigma factor SigE, which in return captures an essential role in sugar catabolism and redox-state regulation. For the purpose of simulating community conditions as found in the field, Microcystis colonies are isolated from the eutrophic lakes near Potsdam, Germany and established as stably growing under laboratory conditions. In co-habitation simulations, the recently isolated field strain FS2 is shown to specifically induce nearly immediate aggregation reactions in the axenic lab strain Microcystis aeruginosa PCC 7806. In transcriptional studies via microarrays, the induced expression program in PCC 7806 after aggregation induction is shown to involve the reorganization of cell envelope structures, a highly altered nutrient uptake balance and the reorientation of the aggregating cells to a heterotrophic carbon utilization, e.g. via glycolysis. These transcriptional changes are discussed as mechanisms of niche adaptation and acclimation in order to prevent competition for resources.},
  language  = {en}
}
@phdthesis{Lamanna2015,
  author    = {Lamanna, Francesco},
  title     = {Adaptive radiation and speciation in African weakly-electric fish},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-80097},
  school      = {Universit{\"a}t Potsdam},
  pages     = {114},
  year      = {2015},
  abstract  = {The rise of evolutionary novelties is one of the major drivers of evolutionary diversification. African weakly-electric fishes (Teleostei, Mormyridae) have undergone an outstanding adaptive radiation, putatively owing to their ability to communicate through species-specific Electric Organ Discharges (EODs) produced by a novel, muscle-derived electric organ. Indeed, such EODs might have acted as effective pre-zygotic isolation mechanisms, hence favoring ecological speciation in this group of fishes. Despite the evolutionary importance of this organ, genetic investigations regarding its origin and function have remained limited. The ultimate aim of this study is to better understand the genetic basis of EOD production by exploring the transcriptomic profiles of the electric organ and of its ancestral counterpart, the skeletal muscle, in the genus Campylomormyrus. After having established a set of reference transcriptomes using "Next-Generation Sequencing" (NGS) technologies, I performed in silico analyses of differential expression, in order to identify sets of genes that might be responsible for the functional differences observed between these two kinds of tissues. The results of such analyses indicate that: i) the loss of contractile activity and the decoupling of the excitation-contraction processes are reflected by the down-regulation of the corresponding genes in the electric organ; ii) the metabolic activity of the electric organ might be specialized towards the production and turnover of membrane structures; iii) several ion channels are highly expressed in the electric organ in order to increase excitability, and iv) several myogenic factors might be down-regulated by transcription repressors in the EO. A secondary task of this study is to improve the genus level phylogeny of Campylomormyrus by applying new methods of inference based on the multispecies coalescent model, in order to reduce the conflict among gene trees and to reconstruct a phylogenetic tree as closest as possible to the actual species-tree. By using 1 mitochondrial and 4 nuclear markers, I was able to resolve the phylogenetic relationships among most of the currently described Campylomormyrus species. Additionally, I applied several coalescent-based species delimitation methods, in order to test the hypothesis that putatively cryptic species, which are distinguishable only from their EOD, belong to independently evolving lineages. The results of this analysis were additionally validated by investigating patterns of diversification at 16 microsatellite loci. The results suggest the presence of a new, yet undescribed species of Campylomormyrus.},
  language  = {en}
}