Chromosome Evolution and Karyotype Diversity in Nigerian Rodents: An Original Comparative Cytogenomic Study Across Six Geopolitical Zones

This dissertation provides the first comprehensive comparative cytogenomic study of chromosome evolution and karyotype diversity in Nigerian rodents, encompassing 65 species and populations from all six geopolitical zones. Rodents are the most speciose mammalian order, and chromosome number and structure are among the most rapidly evolving characters in the group, yet the karyotypic diversity of Nigerian rodent fauna has never been systematically characterised, creating a gap that prevents accurate species delimitation, evolutionary history reconstruction, and conservation unit designation. The dissertation employs a multi-phase cytogenomic design: conventional karyotyping (G, C, and Ag-NOR banding) on 320 specimens from 12 genera across all six zones; fluorescence in situ hybridisation (FISH) using repetitive element probes and telomeric repeats on selected taxa showing divergent karyomorphs; and comparative genomic hybridisation on pairs of cryptic species identified by molecular markers. A phylogenetic analysis of karyotype evolution maps chromosomal rearrangements onto an independently derived molecular phylogeny. The dissertation confirms karyotypic diversity exceeding current taxonomic recognition, with 14 putative cryptic species identified by combined cytogenomic and molecular analysis. Original contributions include the first Nigerian rodent karyotype atlas covering 65 species, a comparative genomic hybridisation dataset revealing interspecific chromosome homology relationships, and a theoretical model of centric fusion as the dominant rearrangement mechanism driving speciation in Mastomys and Arvicanthis. Conservation implications include the identification of six cryptic species requiring independent IUCN assessments. Keywords: karyotype evolution, rodents, cytogenomics, Nigeria, cryptic species.