Historical spatial range expansion and a very recent bottleneck of Cinnamomum kanehiraeHay. (Lauraceae) in Taiwan inferred from nuclear genes

Pei-Chun Liao,Kuo-Chieh Ho,Dai-Chang Kuo,Shih-Ying Hwang,Tsan-Piao Lin,Chia-Chia Lin

doi:10.1186/1471-2148-10-124

Abstract

BackgroundSpecies in the varied geographic topology of Taiwan underwent obvious demographic changes during glacial periods. Cinnamomum kanehirae has been exploited for timber and to obtain medicinal fungi for the past 100 years. Understanding anthropogenic factors influencing the demography of this species after the last glacial maximum (LGM) is critically important for the conservation of this species.ResultsPopulations of C. kanehirae were classified into four geographic regions: northwestern (NW), west-central (WC), southwestern (SW), and southeastern (SE). In total, 113 individuals from 19 localities were sampled, and variations in the chalcone synthase gene (Chs) intron and leafy (Lfy) intron-2 sequences of nuclear DNA were examined in order to assess phylogeographic patterns, the timescales of demographic and evolutionary events, and recent anthropogenic effects. In total, 210 Chs and 170 Lfy sequences, which respectively constituted 36 and 35 haplotypes, were used for the analyses. Estimates of the migration rate (M) through time revealed a pattern of frequent gene flow during previous and the present interglacials. The isolation-by-distance test showed that there generally was no significant correlation between genetic and geographic distances. The level of among-region genetic differentiation was significant when comparing eastern to western populations. However, no significant among-region genetic differentiation was found in comparisons among the four geographic regions. Moreover, essentially no genetic structuring was found for the three regions west of the CMR. A fit of spatial range expansion was found for pooled and regional samples according to the non-significant values of the sum of squared deviations. Using the Bayesian skyline plot (BSP) method, a recent bottleneck after the LGM expansion was detected in both regional and pooled samples.ConclusionsCommon haplotype distributions among geographic regions and the relatively shallow genetic structuring displayed are the result of historical gene flows. Southward dispersals in an earlier time frame from the NW region and in a later time frame from the SE region were inferred. The BSP analysis suggested a postglacial expansion event. Recent trends, however, refer to a bottleneck due to human interventions observed for both pooled and regional C. kanehirae samples.

Highlights

Species in the varied geographic topology of Taiwan underwent obvious demographic changes during glacial periods
Plant materials and DNA amplification In total, 113 individuals originating from 19 populations of C. kanehirae of Taiwan were collected from a scion garden at the Liukuei Research Center, Taiwan Forestry Research Institute (TFRI), southwestern Taiwan (Table 1, Figure 1)
Cinnamomum kanehirae is confronted with conditions of being rare, fragmented, and threatened at the present time, consistent with the genetic survey that revealed a pattern of population growth followed by an ongoing bottleneck

Summary

Introduction

Species in the varied geographic topology of Taiwan underwent obvious demographic changes during glacial periods. Climate change is an important factor influencing organisms' evolutionary history, especially their demographic dynamics [1]. Glacials changed climates in Asia and several refugia of different species are consistently being found [9,10,11,12], which shows that climate changes in the Pleistocene affected the demographic history of Asian species. Conifers which were distributed at high elevations in Taiwan spread to lower elevations to escape the ice-covered mountaintops [14,17,18], and those species originally distributed in middle and low elevations slowly migrated to the lowlands. Climate-dependent changes in demographics of trees in Taiwan are evidenced by the pollen record [19] and genetics, e.g., Michelia formosana (Magnoliaceae) [20], Cunninghamia konishii (Cupressaceae) [21], and Quercus (or Cyclobalanopsis) glauca (Fagaceae) [22]

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Discussion

Conclusion