Population history and seed dispersal in widespread Central American Begonia species (Begoniaceae) inferred from plastome-derived microsatellite markers

Seven plastid microsatellite markers derived from plastome sequence data were used to study the population genetic structure in two widespread Begonia spp. from Central America. In B. nelumbiifolia, no variation was found at any locus. In contrast, significant haplotype diversity was found in B. heracleifolia (h_T = 0.937, h_S = 0.444, 39 haplotypes, mean of 3.3 haplotypes per population), and populations showed high absolute levels of genetic differentiation (G'_ST = 0.829, D = 0.407). The distribution of haplotypes showed strong phylogeographical structure (G_ST = 0.526, R_ST = 0.737, G_ST < R_ST, P < 0.05), but this pattern was poorly accounted for by commonly studied historical scenarios, such as Pleistocene refugia or Pliocene differentiation at the Isthmus of Tehuantepec. Instead, subdivision into a large number of regions, each containing local populations (e.g. when k = 9, F_CT = 0.749, P < 0.05), best explained the haplotype distribution. The lack of haplotype diversity in B. nelumbiifolia, a moist adapted species, suggests that it may have been severely restricted in range during dry spells in the Pleistocene, and has subsequently expanded from this recent population bottleneck. The high haplotype diversity in B. heracleifolia may indicate that its adaptation to drought enabled it to survive in small, but ecologically suitable, pockets of isolated habitat throughout the Pleistocene. Limited seed exchange between B. heracleifolia populations is likely to be responsible for its high population substructure, and provided the opportunity for divergence through genetic drift. This interpretation is consistent with previous population genetic studies in Begonia, and suggests a common pattern of extremely low genetic exchange among a series of small, but long-lived, populations that may predispose the genus to rapid speciation. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 00, 000–000.