Genetic erosion in a tropical tree species demonstrates the need to conserve wide-ranging germplasm amid extreme habitat fragmentation

Comparing the genetic diversity across different generations within tropical tree populations is an understudied topic. To assess the potential genetic consequences and conservation implications of contemporary disturbances, a population genomic study of Palaquium obovatum across age classes was undertaken. Trees and juveniles were sampled from ten different localities (eight in Singapore, two in Peninsular Malaysia) and subjected to double digest restriction-site associated DNA-sequencing (ddRAD-seq) to assess intergenerational genetic differences and investigate population structure in a hexaploid lineage. Genetic erosion, characterised by reduced heterozygosity, was found to have occurred in almost all wild populations over time, the exceptions being in one isolated coastal population and some areas with cultivated occurences. Population structure was highly localised with the number of genetically distinct populations usually following geographically separated districts, which indicates limitations in pollen and seed dispersal between fragments, possibly due to declines in the associated assemblage of dispersers. For this reason, the germplasm for conserving species diversity in degraded habitats and forest fragments should be selected from a wide range of wild populations across the landscape.