Evolutionary Ecology and Phylogeography of Marine Catfish (Ariidae) in Nigerian Coastal Waters

The Ariidae (sea catfishes) are ecologically and commercially important components of Nigerian coastal fisheries, yet their evolutionary history, population genetic structure, and response to historical oceanographic events such as Pleistocene sea level oscillations and river capture remain unknown, limiting understanding of speciation processes and the genetic resources available to support sustainable fisheries. This dissertation provides the first comprehensive phylogeographic and evolutionary ecological study of Nigerian coastal Ariidae, integrating molecular systematics, population genetics, and ecological niche modelling to elucidate diversification history and contemporary population connectivity. Museum specimens and fresh tissue samples from 15 Ariidae species are collected from 22 coastal and estuarine sites spanning all six geopolitical zones of coastal Nigeria, from Badagry to Calabar, during sampling expeditions in 2022 to 2024. A phylogenetic hypothesis for the Nigerian Ariidae is constructed using maximum likelihood and Bayesian inference analyses of mitochondrial cytochrome b, cytochrome oxidase I, and nuclear RAG1 and myh6 gene sequences. Population structure and gene flow among the most commercially important species (Arius latiscutatus, Arius heudeloti, Carlarius parkii) are characterised using restriction site-associated DNA sequencing for population genomics. Divergence dating using a molecular clock calibrated against West African ichthyofaunal biogeographic events tests the hypothesis that Pleistocene sea level lowstands drove population fragmentation and incipient speciation between the Niger Delta and Cross River estuarine populations. Ecological niche models project future range shifts under SSP2-4.5 and SSP5-8.5 climate scenarios. Findings provide the genetic basis for a fisheries unit of management framework. Keywords: Ariidae phylogeography, marine catfish, population genetics, Nigeria, estuarine biogeography