Studies On Conservation Genetics Of The Rare And Endangered Aquatic Plant Caldesia Grandis (Alismataceae)

Biodiversity, sustainable development and global climate change have been considered as the key and the popular subjects of the modern ecological research. Biodiversity refers to the extent of abundance and evenness of species (including animal, plant and microorganism) in an ecosystem, a region and even the earth. The basic characteristics of biodiversity can be dealt with and analyzed in term of four different levels of genetic diversity, species diversity, ecosystem diversity and landscape diversity. As an important component of biodiversity, genetic diversity is the basis of species diversity, ecosystem diversity and landscape diversity. Over the long term, the ability of a species to respond adaptively to environmental changes depends on the level of genetic variability it contains. A species without an appropriate amount of genetic diversity is thought to be unable to cope with changing environments or evolving competitors and parasites. Therefore, investigations of population genetic diversity and the structure of populations within a species may not only illustrate the evolutionary process and mechanism but also provide information useful for biological conservation.Caldesia grandis Samuelsson is a perennial, erect marsh herb belonging to the aquatic family Alismataceae. It is a self-compatible species, which can reproduce both sexually by selfing and out-crossed seeds and vegetatively through bulbils commonly occur in the inflorescences. This species is confined to mountainous bogs and marshes in Southeast Asia. However, only a few records of localities of the species exist. Caldesia grandis in China has been reported from Hubei, Hunan, Yunnan and Guangdong Provinces in Mainland China as well as from the island of Taiwan. In our recent field investigation, only three natural populations including one population in Yunnan Province and two populations in Hunan Province were found in Mainland China. In thepresent study, the mating system and population genetic variations of the rare and endangered marsh plant were studied. The main results are presented as follows:1. Outcrossing rate in an open-pollinated breeding population (LPH population) of C. grandis was estimated by the dominant RAPD marker using 10 open-pollinated progeny arrays of 24 individuals. The multilocus outcrossing rate estimate based on all 25 RAPD loci was 0.872 (± 0.033) and the single-locus outcrossing rate estimate was 0.795 (± 0.032). Multilocus estimate did not significantly differ from the single-locus estimates. The fixation index, F, in the progeny estimated form RAPD data was -0.142 (± 0.000). The estimates of multilocus outcrossing rates (tm) and single-locus outcrossing rates (ts) obtained from MLDT clearly indicate that outcrossing is predominant in the C. grandis open-pollinated breeding population. This is influenced by factors such as plant density, population genetic structure and the adaptability of pollinator as well as the inherent physiological mechanisms. An empirical analysis suggests that 15 is the minimum number of dominant marker loci necessary to achieve robust estimates of tm.2. Genetic variation and clonal diversity of three natural populations of Caldesia grandis were investigated using random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) markers. Both of the markers worked effectively in clone identification of C. grandis. RAPD markers detected more diversity than ISSR markers in the three populations examined. Of the sixty RAPD primers screened, seven produced highly reproducible bands, using these primers, a total of 61 DNA fragments were generated with 52 (85.25%) being polymorphic indicating considerable genetic variation at the species level. Analysis of molecular variance (AMOVA) show that a large proportion of genetic variation (81.5%) resided within populations, while only a small proportion (18.5%) resided among populations. With the use of 52 polymorphic RAPD markers, we were able to identify 127 genets among 342 samples from three populations. The proportion of distinguishable genets (PD: mean 0.37), Simpson's diversity index (D: mean 0.91) and evenness (E: mean 0.78) exhibited high levels of clonal diversity compared to other clonal plants. These results imply that sexual reproduction has played an important role at some time during the history of the population. Nevertheless, the high level of diversity may also be partially generated form the somatic mutations, but it is not likely to account for the high diversity generally found among C. grandis genets.3. The spatial structure of genetic variation of the three populations of C. grandis was investigated using RAPD markers followed by spatial autocorrelation analysis. Atotal of 157 individuals were sampled from four plots and subjected to spatial autocorrelation analysis in two approaches of equal gene frequency and equal distance interval, respectively. Of the polymorphic bands generated by seven selective primers, those polymorphic bands with frequencies ranging from 20 % to 80 % were then used to calculate Moran's / spatial autocorrelation coefficient for each plot. The results revealed that a significant spatial structure of genetic variation existing in the plots in BH and GH populations of C. grandis (with significant positive autocorrelation over short distance class: 1 ~ 2 m). In contrast, the genetic variation in LPH population (Plot 4) was found to be randomly distributed. The different spatial distribution patterns may be attributed to the environment differences. These results have important implications for the conservation and management of the species, especially for the sampling strategies for ex situ conservation.4. Genetic diversity in a natural C. grandis population in Hunan Province was assessed using RAPD markers. A total of 180 individuals from 30 maternal plants were assayed. Of the 100 RAPD primers screened, twelve produced highly reproducible bands, using these primers, a total of 112 DNA fragments were generated with 79 (70.5%) being polymorphic. Analysis of molecular variance (AMOVA) show that a large proportion of genetic variation (76.9%) resided within maternal plants, while only a small proportion (23.1%) resided among maternal plants. Shannon index showed that total genetic diversity of maternal plants was 0.18, which was identical with the result Nei's gene diversity. NTSYS analysis indicated that the offspring individuals from a maternal plant could not be clustered completely together. The estimate of gene flow (Nm) among maternal plants was 0.83, indicating high gene flow existing among the maternal plants.The knowledge of population genetics is a prerequisite for the successful management of conservation programs. This study has increased the understanding of population genetics of C. grandis, which was previously poorly known but which is important for C. grandis conservation. The present study has provided some important baseline data for conservation of C. grandis as well as the other rare and endangered aquatic species.