Genetic diversity of Philippine Rubus moluccanus L. (Rosaceae) populations examined with VNTR DNA probes

Two synthetic DNA probes composed of tandemly repeated 'core' sequences (GACA and GATA) were us ed to examine ge ne tic diversity at multiple variable-number-tandem-repeat (VNTR) loci within and among four spatially isolated Philippine populations of Rubles moluccanus L. (Rosaceae), an uncultivated bramble widely distributed throughout southeast Asia-Malesia. Central goals were to determine whether apomictic propagation was detectable in R. moluccanus and to examine whether populations isolated on separate islands, or on mountain tops on a single island, were genetically differentiated. Sampling 22 individuals per population, the findings include: (1) no two individuals shared identical VNTR band profiles and thus apomictic propagation was not detected; (2) the mean number of bands scored per individual was 24.3 (SD = 3.91) and the proportion of polymorphic loci within populations ranged from 0.69 to 1.00 (mean = 0.86 +/- SD = 0.085); (3) the average proportion of bands shared between individuals within populations ranged from 0.39 to 0.67 (0.50 +/- 0.067), while average interpopulation similarity ranged from 0.21 to 0.50 (0.32 +/- 0.092); and (4) estimated heterozygosity within populations ranged from 0.42 to 0.79 (0.62 +/- 0.083), while interpopulation heterozygosity ran from 0.62 to 0.81 (0.74 +/- 0.062). Permutation tests were used to estimate the statistical significance of differences in similarity between populations. A Luzon population isolated by 1200 km was always significantly different in similarity tests when compared with each of the other three populations, all located on Mindanao (and separated by at least 100 km but less than 250 km). Of the latter three, only one population differed significantly from the other two in the degree of VNTR markers shared, possibly reflecting biogeographic partitioning suggested for the island. Across all populations, average estimated Fst was 0.154, although mean inter-island Fst (0.224) was significantly higher than mean intra-island Pst (0.085). These results suggest that, while intra-island gene flow is relatively high, significant differentiation of tropical species may occur even over short distances on individual islands. Preservation of only a limited number of populations may result in a significant loss of genetic diversity in such species.