An Original Evolutionary Framework for Adaptive Radiation in African Cichlid Fishes of the Niger River, West Africa: Ecological, Genetic, and Morphological Perspectives

This dissertation develops an original evolutionary framework for understanding adaptive radiation in cichlid fishes of the Niger River system, using Nigerian populations from the North Central and South South geopolitical zones as the primary study system. The Niger River cichlid assemblage, comprising over 30 species across the genera Hemichromis, Tilapia, Sarotherodon, and Coptodon, offers a tractable West African model for comparative analysis of adaptive diversification that complements the East African lake radiation models but has received minimal scientific attention. The dissertation integrates morphological analysis, dietary ecology, stable isotope trophic positioning, population genomics (RADseq, 180 individuals, 24 species), and ancestral area reconstruction to characterise the phylogenetic, ecological, and geographic dimensions of cichlid diversification in the Niger system. Geometric morphometric analysis of body and jaw shape captures functional morphological diversity. Dietary specialisation is characterised by gut content analysis and stable isotope biplot clustering. Comparative phylogenetic methods test for rate shifts in morphological diversification along the phylogeny. The dissertation proposes the Niger Cichlid Diversification Framework (NCDF) as an original contribution, demonstrating a decoupled pattern of ecological and morphological diversification, where ecological niche differentiation preceded morphological divergence, a pattern not previously described in African cichlids. Two putative undescribed species are identified by genomic and morphological evidence. The NCDF advances cichlid evolutionary biology theory and provides a phylogenomic basis for species delimitation relevant to fisheries management in the Niger system. Keywords: adaptive radiation, cichlid fishes, Niger River, phylogenomics, evolutionary framework.