Fine- and local- scale genetic structure of Dysoxylum malabaricum, a late-successional canopy tree species in disturbed forest patches in the Western Ghats, India

摘要

Dysoxylum malabaricum (white cedar) is an economically important tree species, endemic to the Western Ghats, India, which is the world's most densely populated biodiversity hotspot. In this study, we used variation at ten nuclear simple sequence repeat loci to investigate genetic diversity and fine scale spatial genetic structure (FSGS) in seedlings and adults of D. malabaricum from four forest patches in the northern part of the Western Ghats. When genetic variation was compared between seedlings and adults across locations, significant differences were detected in allelic richness, observed heterozygosity, fixation index (F (IS)), and relatedness (P < 0.05). Reduced genetic diversity and increased relatedness at the seedling stage might be due to fragmentation and disturbance. There was no FSGS at the adult stage and FSGS was limited to shorter distance classes at the seedling stage. However, there was clear spatial genetic structure at the landscape level (< 50 km), regardless of age class, due to limited gene flow between forest patches. A comparison of the distributions of size classes in the four locations with published data from a more southern area, showed that large trees (diameter at breast height, DBH, > 130 cm) are present in the southern sacred forests but not in the northern forest reserves. This pattern is likely due to stronger harvesting pressure in the north compared to the south, because in the north there are no cultural taboos regulating the extraction of natural resources. The implications for forest conservation in this biodiversity hotspot are discussed.