A Comparative Study Of Genetic Structure Between The Central And Peripheral Populations Of Castanopsis Sclerophylla

Rapid climate change is predicted to lead to species' migrations poleward or upward in elevation and affect the biodiversity significantly.The peripheral populations which always locate in the unfavorable habitats are likely to be sensitive to the climate change,so the species' response to the changing environment mainly depends on that of the peripheral populations.The centralperipheral hypothesis predicts that the peripheral populations have a lower genetic diversity and a higher genetic differentiation.However there are a lot of arguments on it.Castanopsis sclerophylla,a wind-pollinated species of potential high gene flow,is a dominant species of evergreen broad-leaved forests.In this paper,we compared the genetic structure between the central and the peripheral populations to understand whether peripheral populations with high-gene flow species have lower within-population genetic variation and higher among-population variation than central populations have.Using 7 pairs of polymorphic SSR primers,482 samples from 12 central and 5 peripheral populations of C.sclerophylla were analyzed.The mean number of alleles and allelic richness in peripheral populations were not lower,but higher,though not significantly,than those in central populations.Both the observed and expected heterozygosities were significantly higher compared to the central populations.This is due to high gene flow among populations mediated by air currents.During the flowering phase of C.sclerophylla,the dominant air currents are northwestward. Therefore the peripheral populations are recipient and may receive pollen-borne alleles from the central populations,while the central populations could not receive pollen from the peripheral populations.The G_STof the peripheral populations was 0.091,which was lower,but not significantly,than that of the central populations(0.142).The AMOVA indicated that 81%in the total genetic variation was found within populations and 2%was among the peripheral and central populations. The largest genetic distance is between populations RL and PT,while the nearest is between populations TT and YS.Mantel test indicated no relationship between genetic differentiation and geographical distance of C.sclerophylla.Using the software BOTTLENECK,we found significant effects of recent population bottleneck events in three of the five peripheral populations, indicating the peripheral populations might have been extinct and recolonized after the last glacial.