The Molecular Ecology of Plant-Herbivore Interactions in the Rainforest-Savanna Transition Zone of Nigeria: An Original Coevolutionary Study

Plant-herbivore coevolution drives the diversification of plant secondary metabolites and herbivore detoxification mechanisms, yet the molecular ecology of these interactions in the ecologically complex rainforest-savanna transition zone of Central Nigeria, where floristic complexity is highest and interaction networks most intricate, has not been studied. This study investigates the molecular ecology of plant-herbivore interactions in the rainforest-savanna transition zone spanning Kwara, Kogi, and Nassarawa States, making original contributions to coevolutionary theory in West African ecological systems. The study characterised plant secondary metabolite profiles using untargeted metabolomics (liquid chromatography-mass spectrometry) for 45 dominant plant species at 6 sites across the transition zone gradient. Herbivore community composition was assessed by standardised sweep netting, frass DNA barcoding, and camera trapping, totalling 18 months of field data. Plant-herbivore interaction networks were constructed from feeding observations, gut content metabarcoding of 420 herbivore specimens, and controlled feeding preference trials with 12 focal plant-herbivore pairs. Coevolutionary dynamics were assessed using phylogenetic comparative methods (PGLS) to test the prediction that plant-herbivore specialisation correlates with secondary metabolite diversification rate. Results revealed highly modular plant-herbivore networks in which specialist interactions dominate, particularly for alkaloid-rich plant species. Untargeted metabolomics identified 2,847 unique metabolite features, with diversity peaking in forest-edge species at the transition zone boundary. Phylogenetic analysis confirmed a significant positive correlation between plant secondary metabolite diversity and host specificity of associated herbivores. Three novel insect-plant interaction specialisation events were documented. The study makes an original contribution to plant-herbivore coevolutionary theory in tropical transition ecotones.

Keywords: plant-herbivore interactions, molecular ecology, coevolution, transition zone, secondary metabolites