Population structure and speciation in Begonia L.
In order to examine population structure (micro-evolution) in Begonia and its congruence to higher patterns of diversity (macro-evolution), nuclear microsatellite markers have been isolated and applied to two Begonia species, B. socotrana and B. sutherlandii. Begonia socotrana is endemic to the Haggeher Mountains of the island of Socotra in the Indian Ocean, where it has a total range of less than 10 x 15 km. Population surveys have highlighted the need for its conservation status to be reassessed, and it is proposed to reduce its status from 'endangered' to 'least concern'. Population genetic analyses using microsatellite data show a significant degree of population structure (RST= 0.081, P<0.01; q=0.096, P<0.01) and significant isolation by distance, even over small spatial scales. The pattern of isolation by distance could be due to restricted gene flow, or the result of small scale vicariance events in the fragmented peaks of the Haggeher Mountains during climate change and resulting altitudinal migration. Begonia sutherlandii is native to eastern and southern Africa, where it is restricted to shaded, moist banks in indigenous forest. A high degree of population structure was found (q=0.482, P<0.001; RST=0.634, P<0.001), which along with a high number of private alleles reflects the severe isolation of populations in a patchily distributed forest habitat. Population relationships appear to be strongly governed by the history and continuity of forest cover in the region. The population genetic studies of B. socotrana and B. sutherlandii show a strong correlation of genetic variation with geography which reflect patterns seen at larger scales. The correlation of micro and macro evolutionary patterns is congruent with a hypothesis of restricted gene flow promoting speciation in Begonia.