Mating pattern and pollen dispersal in the wild olive tree (Olea europaea subsp cuspidata)

In this study, the mating system, contemporary pollen flow, and landscape pollen connectivity of the wild olive tree (Olea europaea subsp. cuspidata) were analyzed in a fragmented landscape of less than 4-km diameter located in north-western Ethiopia. Four remnant populations of different sizes were investigated. Eight highly polymorphic microsatellite markers were used to genotype 534 adults and 704 embryos. We used contrasting sampling schemes and different methodological approaches to analyze the pollen flow. We observed a lower rate of inbreeding and correlated mating in the fragmented vs. the non-fragmented subpopulation. Using parentage analysis, we detected a bidirectional pollen movement across subpopulations. Pollen flow was found to be directed towards small subpopulations based on parentage and anisotropic analysis. Pollen immigration amounted to more than 50%. Although most pollination occurred within a distance of less than 200 m, longer distance pollen movements of more than 3 km were also detected. Pollen dispersal in the large and dense subpopulation was reduced, and a smaller number of effective pollen sources were detected compared to a smaller fragmented subpopulation. We obtained consistent estimates for the number of effective pollen donors (approximately 6 per mother tree) using three different methods. The average pollen dispersal distance at the landscape level amounted to 276 m while at the local level, 174 m was estimated. Bigger trees were better pollen contributors than smaller trees. We showed here for the first time that pollen dispersal in wild olive follows a leptokurtic distribution.