Population Structure, Parasitic Associations, Distribution Drivers, and Genetic Diversity of Osyris Lanceolata (Hochst. & Steud.) in Uganda and Kenya

Abstract

Osyris lanceolata is highly valued in Africa. The species is endangered due to exploitation and yet among the least studied. Information on the species ecology and genetics is limited in literature. Previous studies revealed knowledge gaps on the species ecology and population genetics which undermines its conservation and threatens livelihoods. To address the existing knowledge gaps, this study was designed to: determine the population structure of O. lanceolata in Uganda; analyse its hosts, habitat qualities and morphology; identify the species’ distribution drivers; and characterize its genetic diversity and structure in Uganda and Kenya. Using the nearest neighbor methods, eleven sites were inventoried and 112 soil samples collected in Karamoja. A total of 210 genetic samples, 96 from Uganda and 114 from Kenya were analysed. A regression analysis of 388 individuals revealed an irregular and poorly regenerating population structure (slope = -4.7058, r2 = 0.2617) with more coppiced individuals (58.7%), fewer seedlings (4%), saplings (46%) and adults (50%). The species density ranged from 5.095 trees ha-1 (Amudat), 27.306 trees ha-1 (Nakapiripirit) and 48.3 trees ha-1 in Moroto District. The species distribution was influenced by highly clustered hosts namely; Euclea racemosa, Rhus natalensis, Maytenus senegalensis, Ozorea insignis, and Terminalia browni as well as habitat qualities such as moderate illumination, rocky surfaces, water gullies and mammal droppings. Multiple regression analysis inferred phosphorus (r2 = 0.6534, p<0.001); nitrogen (r2 = 0.2123, p<0.001), sodium (r2 = 0.3282, p<0.001) and calcium (r2 = 0.3719, p <0.001) as distribution drivers. Kenyan populations showed higher genetic diversity (0.587 - 0.681) than Ugandan populations (0.49 - 0.677). AMOVA revealed greater genetic divergence among individuals (91%), populations (1%), regions (3%) and within individuals (4%). Ugandan populations showed more deviations from Hardy -Weinberg Equilibrium (HWE) than Kenyan populations. STRUCTURE analysis revealed two genetic clusters (K = 2) suggesting emerging evolutionary trends within O. lanceolata taxon that might lead to full allopatric speciation. The findings provide a foundation for developing conservation action strategies to halt further decline in the population and genetic erosion of O. lanceolata and save the species from impeding extinction.