Intra-population Genetic Structure of Camellia hengchunensis Chang

Camellia hengchunensis Chang is an endemic species of Taiwan, which is distributed only on the windward slopes and ridges of Nanjenshan area in the southernmost Taiwan. According to previous research and observation, Camellia is pollinated by insect, often by bees, and the seeds are dispersed mainly by gravity. The object of this study is to use microsatellite markers to help us understand more about the mating system, seed and pollen dispersal, genetic diversity and spatial distribution pattern of C. hengchunensis, and to test two hypothesis about intra-population genetic structure of C. hengchunensis: (1) The genetic structure would be significant but weak at small scale; and (2) Genetic structure would decrease as the size class increases. The results of parentage analysis on 141 samples from Lanjenshi plot and 12 samples near Nanjenlake plot suggest that the outcrossing rate of C. hengchunensis is high. The average seed dispersal distance in Lanjenshi plot is 44.75 m, with a minimum value of 0.286 m and a maximum value of 252.672 m. The average pollen dispersal distance in Lanjenshi plot is 96.371m, with a minimum value of 0 m (when inbreeding) and a maximum value of 265.798 m. Values of Shannon’s information index and Nei’s gene diversity are 0.2712 and 0.1587 respectively in Lanjenshi plot. The Gst value of the two subpopulations in Lanjenshi plot is 0.0236, and the Nm value is 20.6892; the Gst value of Lanjenshi plot and Nanjenlake plot is 0.0761, and the Nm value is 6.0734. All samples in Lanjenshi plot form a clump spatial distribution at all scales, and the genetic structure is significant below 45~60 m. According to minimum DBH for onset of flowering, we divide all samples into three size classes: juveniles, adults and old trees. Both juveniles and old trees are randomly distributed at small scale and show a clump pattern at larger scales in Lanjenshi plot, and the genetic structure of them are not significant at all scales. Adults are aggregated at all scales, and the genetic structure of these individuals is significant below 30 m. The results presented above indicate that seeds of C. hengchunensis are mainly dispersed by gravity, but there might still be other dispersal mechanisms. The pollen dispersal distance can be over 1 km, which makes the genetic divergence between plots not significant. The first hypothesis about genetic structure is supported, which may result from low selfing rate, restricted gene flow, high density of adults and the inverse J-shape population structure. The second hypothesis about genetic structure is not supported, and the possible reasons might be: (1) For unknown reason, only part of “old trees” born “adults”; and (2) Only adults belong to some family survived during the establishing process, because of the heterogeneity of habitat.