An Original Analysis of Nocturnality Evolution and Scotopic Visual Ecology in Nigerian Forest Geckos (Hemidactylus species complex): Phylogenetic, Physiological, and Molecular Evidence

This dissertation provides an original multi-level analysis of the evolution of nocturnality and scotopic visual system adaptations in the Hemidactylus gecko species complex in Nigerian forests, spanning the South West, South East, and South South geopolitical zones. The Hemidactylus complex in Nigeria includes morphologically cryptic species with divergent diel activity patterns, providing a natural comparative system for investigating the molecular and physiological basis of nocturnality evolution at a regional scale. The dissertation employs a four-component design: a molecular phylogenetic analysis of 85 individuals from 12 putative species using mitochondrial and nuclear markers to establish species boundaries and relationships; retinal histology and photoreceptor density analysis across diurnal, crepuscular, and nocturnal taxa; opsin gene sequencing to characterise spectral sensitivity divergence; and visual performance testing by electroretinography under scotopic and photopic conditions. An original Nocturnality Transition Framework (NTF) integrating phylogenetic pattern, retinal, and molecular evidence is proposed. The phylogeny reveals three independent evolutionary transitions to nocturnality within Nigerian Hemidactylus, with correlated shifts in rod:cone ratio, pupil morphology, and opsin spectral tuning. The NTF identifies large pupil size and rod dominance as preceding opsin spectral shifts in the evolutionary sequence, providing original evidence for the sensory morphology-function decoupling hypothesis. The dissertation delivers the first systematic analysis of visual ecology in Nigerian geckos, identifies two putative undescribed species, and provides an original evolutionary framework for nocturnality evolution in tropical lizards. Keywords: nocturnality evolution, Hemidactylus, visual ecology, opsin, Nigerian forest geckos.