Phylogeographic Analysis of Vitellaria paradoxa (Shea Tree) Populations Across the Nigerian Guinea Savanna Using Chloroplast DNA Markers

Vitellaria paradoxa (shea tree) is an economically vital non-timber forest species across Nigerian Guinea savanna, yet its population genetic structure and phylogeographic history across the country's geographic range remain largely uncharacterised, limiting evidence-based management of genetic diversity. This study analysed the phylogeographic structure of Vitellaria paradoxa populations using chloroplast DNA markers (trnL-trnF and rpl16 intron sequences) across 12 populations distributed across the Nigerian Guinea savanna zone, from Kogi and Kwara States in the South to Katsina and Jigawa States in the North. Leaf tissue from 15 individuals per population was sampled, DNA was extracted, and target regions were amplified by polymerase chain reaction and sequenced. Haplotype networks were constructed using TCS software. Population genetic parameters including haplotype diversity, nucleotide diversity, and neutrality tests were calculated. Analysis of molecular variance was performed to partition diversity within and among populations. Eighteen chloroplast haplotypes were identified across all populations. Haplotype diversity was higher in southern populations (Kwara, Kogi) compared to northern populations (Katsina, Jigawa), consistent with a northward expansion model. Analysis of molecular variance revealed that 68% of total genetic variation partitioned among rather than within populations, indicating significant genetic structuring. Northern and southern population groups were genetically distinct with low gene flow. The study concludes that shea tree populations in Nigeria harbour significant phylogeographic structure, and recommends that domestication programmes maintain separate northern and southern breeding populations to preserve adaptive genetic diversity.

Keywords: Vitellaria paradoxa, shea tree, phylogeography, chloroplast DNA, Guinea savanna