Long pollen dispersal prevents biparental inbreeding depression in seeds in a natural population of the tropical tree Shorea laxa

Abstract

The aim of this study was to detect biparental inbreeding depression in seeds in a natural population of the tropical tree Shorea laxa. Using microsatellite markers, we conducted parentage analysis and directly estimated outcrossing rate and contemporary pollen dispersal across a natural population (100 ha). We found a high outcrossing rate and frequent long pollen dispersal in S. laxa, even though the population-level flowering during the study was not intensive. We also found a significant but weak negative correlation between pairwise relatedness and spatial distance between adult trees. Structural equation modeling revealed significant decrease in seed size with increasing pairwise relatedness of seed parents, indicating biparental inbreeding depression and also indicating a positive contribution of maternal internal relatedness and a negative contribution of pollen dispersal distance to the relationships among seed size and pairwise relatedness of seed parents. These results suggest that long-distance pollen dispersal is essential to prevent biparental inbreeding depression in S. laxa. When developing conservation strategies for S. laxa, attention must be paid to the breeding structure and phenology to ensure long-distance pollen dispersal and prevent reproductive isolation and inbreeding.