A conservation genetic study of Rafflesia speciosa (Rafflesiaceae): patterns of genetic diversity and differentiation within and between islands

Rafflesia speciosa is a threatened endo-holoparasitic species. It has several populations in the Central Panay Mountain Range (CPMR) of Panay island and a single population on Negros Island. Because R. speciosa is the only Philippine species of the genus that is not endemic to an individual island, it is a suitable species for improving our understanding of the factors underlying the high island endemism of Philippine Rafflesia. For this purpose and to inform the conservation management of R. speciosa, patterns of genetic diversity and differentiation were studied using 15 microsatellite loci and samples from nine populations. None of these populations shows evidence of inbreeding and R. speciosa has similar levels of heterozygosity as generally observed in outcrossing or perennial plant species. The results of AMOVA and Bayesian cluster analyses indicate that the Negros population is genetically differentiated from the CPMR populations. In addition, it has lower genetic diversity than similar-sized R. speciosa populations. These findings suggest that sea straits potentially provide significant reproductive barriers to Rafflesia species, and are perhaps responsible for their high island endemism. The general lack of genetic differentiation among the CPMR populations as suggested by the AMOVA, PCoA, and STRUCTURE results indicates recent gene flow among them and this finding improves our understanding of the geographical scale and context at which gene flow between Rafflesia populations occurs. Conservation efforts should be targeted towards avoiding further habitat degradation in the Negros population. We also recommend protective status for the entire CPMR and reforestation efforts to mitigate the severe habitat fragmentation, destruction, and degradation in this area.