Pattern and processes of cichlid speciation along a geographical gradient in the Lower Congo River: Are species complex genomic networks?

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Inter- and intraspecific gene flow is increasingly recognized as an important factor shaping diversification and speciation. We study the phylogeny, phylogeography and population genomics of five small cichlid species assemblages (Teleostei: Cichlidae; 3-10 species each) endemic to the rapids of the Lower Congo River. The parallel evolution of five morphological and/or ecological divergent lineages of the genera Steatocranus, Nanochromis, Haplochromis, Teleogramma and Lamprologus within the contiguous unidirectional topography of the Lower Congo River allows testing of speciation with gene flow and hybrid speciation hypotheses under parapatric and partially sympatric geographical settings. Building on own previous phylogeographic and morphometric results, we will take advantage of Next Generation Sequencing, stable isotope analysis and geometrical morphometrics to assess genome-phenotype-environment associations for each cichlid assemblage along an approximately 16 km long stretch of the Lower Congo River at the rapids of Inga. This approach will give us the opportunity (1) to identify and compare genomic signatures of adaptive vs. non-adaptive parapatric population divergence across species under identical conditions. It will further allow to (2) identify and analyze changes of genomic architecture after secondary introgression and, in at least one case, after homoploid hybrid speciation, which most likely took place after secondary contact of previously allopatric lineages. The study will contribute to the general understanding of the role of introgression and hybridization for the origin of new species.