AOBPreview originally published online on June 21, 2006
Annals of Botany 2006 98(2):449-457; doi:10.1093/aob/mcl123
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Genetic Diversity and Geographic Differentiation in Tacca chantrieri (Taccaceae): an Autonomous Selfing Plant with Showy Floral Display
1 Laboratory for Plant Biodiversity and Biogeography, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan 650204, China, 2 Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Mengla, Yunnan 666303, China and 3 The Graduate School of Chinese Academy of Sciences, Beijing, 100049, China
* For correspondence. E-mail dzl{at}mail.kib.ac.cn
Received: 25 December 2005 Returned for revision: 27 March 2006 Accepted: 12 April 2006 Published electronically: 21 June 2006
• Background and Aims Despite considerable investment in elaborate floral displays, Tacca chantrieri populations are predominantly selfing. It is hypothesized that this species might possess considerable spatial or temporal variation in outcrossing rates among populations. To test this hypothesis, genetic variability and genetic differentiation within and among T. chantrieri populations were investigated to find out if they are in agreement with expectations based on a predominantly inbred mating system.
• Methods Genetic diversity was quantified using inter-simple sequence repeats (ISSR) in 303 individuals from 13 populations taken from known locations of T. chantrieri in China, and from one population in Thailand.
• Key Results Of the 113 primers screened, 24 produced highly reproducible ISSR bands. Using these primers, 160 discernible DNA fragments were generated, of which 145 (90·62 %) were polymorphic. This indicated considerable genetic variation at the species level. However, there were relatively low levels of polymorphism at population levels, with percentages of polymorphic bands (PPB) ranging from 8·75 % to 55 %. A high level of genetic differentiation among populations was detected based on different measures (Nei's genetic diversity analysis: GST = 0·5835; AMOVA analysis: FST = 0·6989). Furthermore, based on levels of genetic differentiation, the 14 populations clustered into two distinct groups separated by the Tanaka Line.
• Conclusions High levels of differentiation among populations and low levels of diversity within populations at large spatial scales are consistent with earlier small-scale studies of mating patterns detected by allozymes which showed that T. chantrieri populations are predominantly selfing. However, it appears that T. chantrieri has a mixed-mating system in which self-fertilization predominates, but there is occasional outcrossing. Significant genetic differences between the two distinct regions might be attributed to vicariance along the Tanaka Line. Finally, possible mechanisms of geographic patterns based on genetic differentiation of T. chantrieri are discussed.
Key words: Tacca chantrieri, floral display, population genetic structure, gene flow, ISSR markers, mating system, geographic differentiation, Tanaka Line