Phylogeography of an Alpine Species Primula Secundiflora Inferred From
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Journal of Systematics and Evolution 46 (1): 13–22 (2008) doi: 10.3724/SP.J.1002.2008.07049 (formerly Acta Phytotaxonomica Sinica) http://www.plantsystematics.com Phylogeography of an alpine species Primula secundiflora inferred from the chloroplast DNA sequence variation 1,4Feng-Ying WANG 2Xun GONG 1Chi-Ming HU 3Gang HAO* 1(South China Botanical Garden, the Chinese Academy of Sciences, Guangzhou 510650, China) 2(Kunming Institute of Botany, the Chinese Academy of Sciences, Kunming 650204, China) 3(College of Life Sciences, South China Agricultural University, Guangzhou 510642, China) 4(Graduate University of Chinese Academy of Sciences, Beijing 100049, China) Abstract The Hengduan Mountains (HM) and adjacent regions have been suggested as the important refugia of the temperate plants during the glacial stages. However, it remains unknown how the HM endemic species can respond to the climatic oscillations. In this study, we examined the chloroplast trnL-trnF and rps16 sequence variation of Primula secundiflora, a relatively common alpine perennial endemic to this region. Sequence data were obtained from 109 individuals of 11 populations covering the entire distribution range of the species. A total of 15 haplotypes were recovered and only one of them is commonly shared by three populations while the others are respectively fixed in the single population. The total diversity (HT=0.966) is high while the within-population diversity (HS=0.178) is low. Despite the high uniformity of the intraspecific morphology, an analysis of molecular variance (AMOVA) revealed a high level of genetic differentiation (97.65%) among populations. The higher NST (0.982) than GST (0.816) (P<0.05) suggested a distinctly phylogeographical pattern. Phylogenetic analyses of haplotypes identified four major clusters of the recovered haplotypes: three clades in the north, and the other one in the south. The isolated distribution of clades suggested multiple refugia of this species during the glacial stages. We failed to detect the interglacial or postglacial range expansion of this species as revealed for the other temper- ate plants. However, the low intra-population diversity suggested that most of the populations should have ex- perienced the in situ shrink-expansion cycles during the climatic oscillations. This inference was further supported by the nested clade analysis, which indicated that restricted gene flow with isolation by distance and allopatric fragmentation were likely the major processes that shaped the present-day spatial distribution of haplotypes in this species. Such a special phylogeographic pattern may have resulted from a combination of both climatic oscillation and complex topology of HM. Key words Phylogeography, Primula secundiflora, cpDNA, trnL-trnF, rps16, Hengduan Mountains. Hengduan Mountains (HM) in the southeast promoted the divergences of intraspecific lineages and Qinghai-Tibetan Plateau (QTP) comprise the major consequently leaded to adaptive diversification of component of the south-central “biodiversity hotspot”: plants (Wang & Liu, 1994; Sun, 2002; Wang et al., one of the 25 areas recognized globally as featuring 2005; Liu et al., 2006). These hypotheses were partly exceptional concentrations of endemic species (Myers confirmed in a few species-rich genera at the species et al., 2000). This region consists of a series of spec- level (Li & Li, 1993; Wang et al., 2004, 2005, 2007; tacular north-south trending ridges alternating with Liu et al., 2002, 2006). However, very few population deep valleys, with altitudes ranging from 2000 to 6000 genetic analyses have been conducted on the species m a.s.l. (Shi et al., 1998) and contains more than occurring in HM and therefore the phylogeographic 12000 species of plants and is especially rich in patterns, intraspecific divergence and glacial refugia endemic species and genera (Ying & Zhang, 1984, remains largely unknown in this region. The few 1993; Li & Li, 1993; Li, 1994; Hao, 1997; Wang, phylogeographic studies focused on the species dis- 2000). The production of such high diversity was tributed in the north of HM, mostly from the QTP suggested to be due to two major factors: (i) this platform, and these studies suggested that these spe- region served as an important refugium that harbored cies responded extensively to the past climatic oscilla- the ancient species; and (ii) the uplifts of the QTP as tions (e.g. Zhang et al., 2005; Meng et al., 2007). A well as the Quaternary climatic oscillations further few of them (Zhang et al., 2005) had experienced a ——————————— similar glacial retreat and postglacial range shift as Received: 19 March 2007 Accepted: 24 May 2007 those temperate organisms in Europe and North * Author for correspondence. E-mail: [email protected]; Tel.: 86-20- America during the past climatic oscillations (Avise, 38635898; Fax: 86-20-85282180. 14 Journal of Systematics and Evolution Vol. 46 No. 1 2008 1998; Comes & Kadereit, 1998; Hewitt, 1996, 2000, 1 Material and methods 2004; Newton et al., 1999; Widmer & Lexer, 2001; Abbott & Brochmann, 2003). However, this scenario 1.1 Plant materials might not have occurred in the southeast QTP because Leaf materials of Primula secundiflora were the high mountains and deep valleys may have sampled from almost the entire range of species, blocked the interglacial or interglacial range expan- including western Sichuan, north-western Yunnan and sion of plants. This topological effect might have south-eastern Xizang (Tibet) in HM (Table 1; Fig. 1). accelerated inter-population differentiation but re- Nine or 10 individuals from each population were tained multiple refugia of plants during glacial cli- collected, with samples at least 10 m apart. In total, matic oscillations. In order to test this prediction, in 109 individuals from 11 populations were used in the the present study, we aimed to recover the phy- present study. Leaf material was dried in silica gel and logeographic pattern of another alpine perennial that is stored at room temperature. endemic to HM. 1.2 DNA extraction, PCR amplification and se- Primula L. is one of the species-rich genera in quencing the HM and adjacent regions of the QTP with more Total DNA was extracted using the CTAB than 75% of the total number of species (ca. 425) method (Doyle, 1991). PCR amplification and DNA distributed in this region (Hu, 1994; Richards, 2002). sequencing were performed with universal primers for Despite the lack of the detailed research, the diversi- trnL-trnF (5′-CGAAATCGGTAGACGCTACG-3′ and fication of this genus may have similar causes as those 5′-ATTTGAACTGGTGACACGAG-3′; Taberlet et revealed for other species-rich genera (Wang et al., al., 1991; Zhang et al., 2006) and rps16 (5′-GTGGTA- 2004, 2005, 2007; Liu et al. 2002, 2006). Primula GAAAGCAACGTGCGACTT-3′ and 5′-TCGGGA- secundiflora Franch. is endemic to HM and sparely TCGAACATCAATTGCAAC-3′; Oxelman et al., distributed in alpine habitats of this region. In addi- 1997). Polymerase chain reaction (PCR) was con- tion, this perennial species has a wide geographical ducted in a total volume of 50 µL containing 20 ng coverage from west Sichuan to northwest Yunnan and template DNA, 5 µL 10×reaction buffer, 5 µL MgCl2 southeast Tibet (Hu, 1990; Hu & Kelso, 1996). This (25 mmol/L), 1 µL dNTP mix (10 mmol/L), 10 species displays the high uniformity in morphology µmol/L of each primer, and 1.5 unit of Taq poly- (Hu, 1990) and our field investigations failed to find merase. PCR reaction was run in a DNA Programma- any intraspecific variations. This species provides a ble Thermal Cycler (PTC-200, MJ Research) with good model to investigate the intraspecific genetic initial denaturation at 94 ℃ for 5 min, followed by 34 divergence and phylogeographic structure of alpine cycles of 1 min at 94 ℃, 1 min of annealing at 56 ℃ species in HM. We used the chloroplast (cp) trnL-trnF and 59 ℃, respectively, for trnL-trnF and rps16, 1 and rps16 sequence variations to explore the genetic min at 72 ℃, and a subsequent 7 min of final exten- structure of this species. The phylogeographic struc- sion at 72 ℃. Sequencing reactions were performed tures constructed by cpDNA may accurately reflect by using the dye-terminator cycle-sequencing ready- range shifts and population dynamics of plants be- reaction kit following the manufacturer’s protocol, cause this genome is maternally inherited in most and analyzed on an ABI 377 DNA Sequencer (Ap- angiosperms (Schaal et al., 1998; Newton et al., 1999; plied Biosystems, Foster City, CA 94404, USA). Soltis & Gitzendanner, 1999). The phylogeographic 1.3 Data analysis patterns of plants in other regions based on cpDNA The DNA sequences were aligned using the pro- sequence variations have been revealed to correspond gram Clustal X 1.81 (Thompson et al., 1997). Esti- well with the past range shifts and population dynam- mates of average gene diversity within populations ics inferred from pollen and glacial or climatic signa- (HS), total gene diversity (HT) and the proportion of tures (Fujii et al., 2002; Okaura & Harada, 2002; total diversity due to differences between populations Newton et al., 1999; Petit et al., 2003; Bartish et al., (GST and NST) were calculated using the program 2006). Overall, our objectives in this study were: (i) to PERMUT (Pons & Petit, 1996, available at http: establish the phylogeographic structure of P. secundi- //www.pierrton.intra.fr/genetics/labo/software/permut). flora based on the sequence variations of two cpDNA GST is calculated solely based on haplotype frequencies, fragments; and (ii) to test whether this species has a whereas NST takes into account the genetic relation high inter-population differentiation and had possibly among haplotypes. When NST value is higher than the retained multiple separate refugia during the glacial GST estimated, it indicates the presence of a phylogeo- stages. graphical structure (Petit et al., 2005). WANG et al.: Phylogeography of Primula secundiflora inferred from cpDNA sequence variation 15 Table 1 Sample locations of Primula secundiflora and genetic estimates of diversity within the studied populations Pop.