Abstract
Cycads, an ancient plant lineage originating ~270 million years ago, are dioecious species relying on scent for insect-mediated pollination. The genus Encephalartos, endemic to Africa, is a rapidly diversified lineage under significant extinction risk due to reproductive failure. While their pollinators (Porthetes sp., Metacucujus spp., and Erotylidae) and their use of male cones as brood sites are known, the taxonomy of African Erotylidae remains largely unstudied at the molecular level. Furthermore, the non-pollinating seed predator Antliarhinus spp. inflicts 90-100% seed loss by developing in female cones and preying on ovules, yet its chemical ecology in relation to Encephalartos spp. is unknown. This study aimed to bridge these knowledge gaps by investigating the ecology of odour communication between Encephalartos spp. and Antliarhinus spp., and the taxonomy of African Erotylidae. The research pursued four objectives: i) identify African cycad-pollinating Erotylids using DNA barcoding, ii) test Antliarhinus responses to Encephalartos odour cues, iii) understand factors predisposing cycad seeds to predation along elevational gradients using E. villosus, and iv) assess the impact of Antliarhinus predation and cycad sex ratio on E. villosus fecundity in varying aggregations. Data were collected in the period of two years, in the Oribi Gorge Nature Reserve and Umtamvuna Nature Reserve, South Africa, and analyzed using various statistical methods in R, including Structural Equation Models and generalized linear models. Key findings include: i) Despite sequencing challenges, phylogenetic analysis of African Erotylidae revealed at least nine potential beetle species, indicating high diversity. ii) Y-maze olfactometer assays showed that both male and female Antliarhinus zamiae were attracted to volatile organic compounds (VOCs), with females exhibiting stronger responses. Critically, a ternary blend of (3E)-1,3-octadiene, linalool, and benzaldehyde, known to attract pollinators, also strongly attracted A. zamiae, suggesting their exploitation of pollinator-attracting cues. iii) For E. villosus, seed production decreased while seed predation increased with elevation, with open habitats
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yielding significantly more seeds and lower predation. iv) Population dynamics of E. villosus showed a stable population growth rate (λ=1) across habitats and elevations, with a high proportion of seedlings and high elasticity for seedling stage stasis. This research represents the first DNA barcoding study of African Erotylidae and the first investigation into the chemical ecology of Antliarhinus spp. in relation to Encephalartos spp. in Africa. We firstly recommend intensive field surveys for more specimens needed from all African cycads to improve the success rate of DNA sequencing. Close work between entomologists and molecular biologists of South Africa and other African Universities to describe these species, Erotylidae sp., by using DNA barcoding. This will help to differentiate closely related cycad species and improve the accuracy of taxonomic classification within the genus at the species level. Secondly, more research to quantify VOCs concentration and determine the threshold of chemical compounds that attract (blends) herbivores from female cones of E. villosus. Investigate local traditional uses of cycad species and correlate these with phytochemical analyses. Thirdly, document microclimate, substrate (soil, rock, tree type), and associated vegetation for cycad species to understand their niche specialization. Lastly, conduct further longitudinal studies for at least four years to understand how habitat type and elevation influence population trajectories over time, and to better predict the dynamics of the E. villous population in the study site.