Genetic diversity and origin of Potamogeton anguillanus (Potamogetonaceae) in Lake Biwa,Japan

We analyzed the genetic variation in Potamogeton anguillanus Koidz. and its putative parents, P. malaianus Miq. and P. perfoliatus L., at five allozyme loci of four enzymes to test the hypothesis of a hybrid origin for P. anguillanus, collected in Lake Biwa, Japan. Alleles diagnostic for either P. malaianus or P. perfoliatus were present at four loci. Of 13 single locus phenotypes (SLPs) of P. anguillanus, eight were phenotypes that were expected in F(1) hybrids between P. malaianus and P. perfoliatus. Two SLPs were different from those expected in F(1) hybrids but could have resulted from segregation of parental alleles in later generation hybrids. Each of the remaining three SLPs possessed one allele unique to P. anguillanus. Allozyme analyses thus supported the view that P. anguillanus was derived from hybridization between P. malaianus and P. perfoliatus. It seems likely that the genetic diversity of P. anguillanus found previously originated through multiple hybridizations and sexual processes in P. anguillanus. Other processes such as intragenic recombination, mutation, or hybridization with another lineage are also discussed with reference to the origin of unique alleles.     

Genetic diversity and origin of <Emphasis Type="Italic">Potamogeton anguillanus</Emphasis> (Potamogetonaceae) in Lake Biwa,Japan

We analyzed the genetic variation in Potamogeton anguillanus Koidz. and its putative parents, P. malaianus Miq. and P. perfoliatus L., at five allozyme loci of four enzymes to test the hypothesis of a hybrid origin for P. anguillanus, collected in Lake Biwa, Japan. Alleles diagnostic for either P. malaianus or P. perfoliatus were present at four loci. Of 13 single locus phenotypes (SLPs) of P. anguillanus, eight were phenotypes that were expected in F₁ hybrids between P. malaianus and P. perfoliatus. Two SLPs were different from those expected in F₁ hybrids but could have resulted from segregation of parental alleles in later generation hybrids. Each of the remaining three SLPs possessed one allele unique to P. anguillanus. Allozyme analyses thus supported the view that P. anguillanus was derived from hybridization between P. malaianus and P. perfoliatus. It seems likely that the genetic diversity of P. anguillanus found previously originated through multiple hybridizations and sexual processes in P. anguillanus. Other processes such as intragenic recombination, mutation, or hybridization with another lineage are also discussed with reference to the origin of unique alleles. Received: March 16, 2001 / Accepted: September 11, 2001     

Aquatic macrophyte composition in relation to environmental factors of irrigation ponds around Lake Shinji,Shimane, Japan

A comparative study of aquatic vegetation of 149 irrigation ponds in the surrounding area of Lake Shinji, Shimane Prefecture, Japan, was done to document the present status of aquatic flora and water chemistry. In addition, influence of 17 environmental factors on the between-pond variation in aquatic macrophyte composition was assessed by using detrended correspondence analysis (DCA). A total of 38 taxa were recorded, and the most frequent taxon was Trapa spp. (>50%). Number of taxa per pond ranged from 1 to 14 and mean number was 4.1. Floristic composition was primarily related to variation of the factors such as conductivity, Mg, Ca, Na, alkalinity, altitude, pH and depth. In contrast, no significant correlations were found with total P, PO₄-P, transparency, COD, ignition loss of bottom soil, Mn and Fe. Of the 33 significant species associations between 19 species with more than 5% frequency occurrence, 28 were positive and the remaining 5 were negative. All of these negative associations involved Trapa spp., and not only water chemistry but some other factors like competition and bottom soil preference were assumed to influence species associations.Abbreviations (DCA) Detrended Correspondence Analysis     

Genetic diversity of the submerged macrophyte Hydrilla verticillata (L. f.) Royle in a river system in Japan

The genetic diversity of Hydrilla verticillata was studied in the Kako River system, Hyogo Prefecture, southwestern Japan, including some of its tributaries. Sex expression (monoecy or dioecy), ploidy level (diploid or triploid), and isoenzyme phenotypes were investigated for plant samples collected from 51 sites along the water course. Monoecious plants occurred at 10 sites and dioecious plants at 47 sites. Among dioecious plants, diploid and triploid plants occurred at 1 and 46 sites, respectively. Seven multienzyme phenotypes (MEPs) were recognized by electrophoretic analysis among dioecious triploid plants. The distribution pattern of nine biotypes based on sex expression, ploidy level, and MEPs suggested the possibility of ecological differentiation among different biotypes. The implications of genetic diversity demonstrated in this study were discussed in relation to the conservation strategy of biodiversity in a river system. Received: April 12, 1999 / Accepted: July 7, 1999     

Aquatic plants diversity in arid zones of Northwest China: patterns, threats and conservation

We investigated aquatic plant diversity by conducting the field investigation and collecting the published data in the arid regions of Northwest China. Two hundred and twenty four taxa of vascular aquatic plants representing 64 genera and 34 families occur in this area, 8.48% of which are endemic. Among these, 1 genus and 6 species were new state records and 1 family, 9 genera and 29 species were new area records. Typhaceae, Potamogetonaceae, Juncaginaceae and Haloragaceae were the most frequent families (considering relative frequency of occurrence), whereas Cyperaceae, Potamogetonaceae and Ranuncnlaceae are the most species-rich. The most frequent genera were Typha, Potamogeton, and Triglochin, and the most species-rich were Potamogeton, Eleocharis and Scirpus. The most frequent species are Triglochin palustre, Myriophyllum spicatum, Potamogeton pectinatus and Typha angustifolia. Aquatic plants diversity is distributed unevenly in the region. The maximum species occurs in Dzungarian basin while the least species in Hexi corridor. The aquatic flora in arid zone of China is not distinctive although some endemic species are found, most species are widely distributed. Local aquatic plants diversity can be influenced by many factors such as hydrological alteration, habitat loss, over-grazing, high human population pressure, global climate change, an inappropriate economic development policy. Among them, the largest threat to aquatic plants biodiversity may be habitat loss due to hydrological alteration. In order to conserve the aquatic plants biological resources and biodiversity in this region, some strategies and measures must be suggested including strengthening scientific research and biodiversity education in the local people, balancing economic development and ecological conservation, and enhancing governmental assistance and subsidy to the local residents.     

Population genetics of threatened wild plants in Japan

Approximately one-fourth of Japan's native plant species are threatened with extinction. To conserve these species, it is critical to evaluate genetic diversity at species-level and population-level. Some factors, including population size and geographic distribution, are known to influence the population genetic diversity of wild plant species. This article briefly reviews the population genetic studies that have been conducted on wild threatened plants in Japan. A large population size or wide geographic distribution does not always lead to large genetic diversity, suggesting that historical factors such as speciation processes and population expansion often play more important roles in determining genetic diversity than the number of remnant individuals. The mating system of a species also affects genetic diversity; predominantly selfing species tend to have smaller genetic diversity than outcrossing congeners. Another issue of concern in the conservation genetics of wild plants in Japan is the genetic diversity of insular endemics, because Japan consists of many islands, and the insular flora contains many endemic and threatened species. Previous studies on endemic plants on the Bonin and the Ryukyu Islands are reviewed. Compared to the cases of the Bonin Islands or other oceanic islands, there is much larger genetic diversity in plants endemic to the Ryukyu Islands. This difference is probably the result of the differences in the geological history of these islands. Electronic Publication     

Echosounding observations of coverage,height, PVI,and biomass of submerged macrophytes in the southern basin of Lake Biwa,Japan

We have developed a procedure to process echosounding data to map the distribution of submerged aquatic macrophytes in the southern basin of Lake Biwa, a water body that has a surface area of 52 km² and a mean depth of 4 m. Echosounding observations were made along 27 transect lines spaced at 500-m intervals on August 4 and September 2 and 30, 2003. Quantitative vegetation data including percent coverage, mean vegetation height, and percent vegetation infestation were directly determined using image data from the echosounder recorded digitally on videotape. Based on the image data from an echosounder, a regression model was developed for estimating biomass of submerged macrophytes. The regression model using the total echo strength as the explanatory variable could reliably estimate macrophyte biomass up to 300 g m⁻². Distribution maps of macrophyte height and biomass suggest that the recent summer decline of submerged macrophytes started earlier in shallow areas (<3 m of depth) than deep areas (>4 m) in the southern basin of Lake Biwa.     

Seasonal variation of dissolved aluminum concentration in harmonic-type Lake Biwa, Japan

Monthly observations performed on a typical harmonic-type lake, Lake Biwa (latitude 35°15′ N, longitude 136°05′ E, Japan), showed that the particulate aluminum concentration varied around a mean value of 0.8 μM, with occasional extraordinarily high values, whereas the dissolved aluminum concentration varied, in the surface layer of the whole lake, between a minimum of 0.01 μM and a maximum of 0.30 μM, depending on the season. Although the variation in dissolved aluminum paralleled the variation in the pH of the lake water, the variation in dissolved aluminum lagged behind the variation in pH by approximately 1 month. A series of laboratory incubation experiments suggested that the supply of dissolved aluminum from, and its removal by, the suspended particulate matter involved a slow, pH-dependent reaction. The stoichiometry and the apparent equilibrium constant of this reaction were evaluated by adopting a zeolite-like structure for the surfaces of the suspended particulates. Received: December 28, 2000 / Accepted: August 22, 2001     

Evaluation of the extent of genetic variation in mahoganies (Meliaceae) using RAPD markers

Despite the economic importance of mahoganies (Meliaceae) little is known of the pattern of genetic variation within this family of tropical trees. We describe the application of a polymerase chain reaction (PCR)-based polymorphic DNA assay procedure random amplified polymorphic DNAs (RAPDs) to assess the extent of genetic variation between eight mahogany species from four genera. Pronounced genetic differentiation was found between the species and genera. There was a clear separation of Cedrela odorata from the other species, with 95% of the variable amplification products differing, whereas Lovoa trichilioides, Khaya spp. and Swietenia spp. were more closely grouped. These results are consistent with the current taxonomic viewpoint. A number of markers were found to be diagnostic for particular species, which could be of value in determining the status of putative hybrids. The application of RAPDs to the study of genetic variation in mahoganies is discussed in the context of developing genetic conservation and improvement strategies for these species.     

Microsatellite and chloroplast DNA analyses reveal no genetic variation in a beach plant Surianana maritima on the Paracel Islands,China

Genetic variation within and among six natural populations of beach plant Suriana maritima on the Paracel Islands of China was assessed using SSR and chloroplast DNA sequence analysis. The results showed a complete absence of genetic variation between individuals either within or among populations. The cumulative consequences of a founder effect, selfing, and inbreeding may be responsible for the loss of genetic diversity in S. maritima.     

Environmental gradients determining the distribution of benthic macroinvertebrates in Lake Takkobu, Kushiro wetland, northern Japan

Effects of environmental variables on the distribution of benthic macroinvertebrates inhabiting sediments were studied at 25 sites along the shoreline of Lake Takkobu in the Kushiro wetland of northern Japan in summer 2003. During the last decade, the lake’s status has undergone a drastic shift from clear water dominated by submerged macrophytes to turbid water dominated by phytoplankton. The canonical correspondence analysis showed that four environmental variables explained the significant variation in the macroinvertebrate species composition: submerged plant biomass, bottom sediment organic matter content (OMC), distance from the mouth of the Takkobu River, and bottom-layer pH. Five species of Chironomidae [Chironomus sp. (except plumosus group), Psectrocladius sp., Corynoneura sp., Parachironomus sp. arcuatus group, and Zavreliella sp.] occurred in sites with relatively lower pH and a high submerged plant biomass, whereas three species of Tubificidae (Tubifex tubifex, Aulodrilus limnobius and Aulodrilus sp.) and two of Chironomidae (Nanocladius sp. and Monodiamesa sp.) occurred in sites with high pH and little vegetation. The three Tubificidae species also preferred organic-rich sediments. Irrespective of aquatic vegetation, Sphaerium sp. (Bivalvia) and Monodiamesa sp. (Chironomidae) occurred in low-OMC sites, whereas Tanypus sp. (Chironomidae) preferred high-OMC sites. The number of macroinvertebrate taxa showed the highest correlation with the number of submerged plants, suggesting that macroinvertebrate species richness was related mostly to submerged plant species diversity in this lake. The quantity and species richness of submerged plants and OMC are thus important determinants of the community structure of macroinvertebrates inhabiting sediments in Lake Takkobu.     

Numerical study on amelioration of water quality in Lakes Shinji and Nakaumi: a coastal brackish lagoon system

Aiming at estimating the effect of an amelioration scheme for water quality in a highly eutrophicated and strongly enclosed estuary, especially placing emphasis on the alleviation of a oxygen-depleted water body, a three-dimensional (3-D) time-dependent coupled physical and ecological model was applied to Lakes Shinji and Nakaumi, a typical coastal brackish lagoon system in Japan. First, the model was run to reproduce the seasonal variation in water temperature, salinity, dissolved oxygen, and other ecological constituents during the period from April 1998 to March 1999. The daily change regimes of the observed sea surface winds, tidal elevation at the open boundary, river discharges, and meteorological parameters were incorporated into the forcing variables of the ecosystem model. Next, as a numerical experiment, a scenario simulation was carried out under four premises to alleviate the oxygen-depleted water body. The model results agreed fairly well with the field measurements obtained through the regular environmental monitoring in the lagoon system. It was found that an oxygen-depleted water body appears in the eastern part of Lake Nakaumi in early May and develops to cover the whole lagoon in midsummer to leave it almost anoxic. The scenario simulation revealed that each amelioration scheme has a considerable effect in alleviating this hypoxic water body. It was found from the model results and the additional flux analyses that the oxygen concentration will improve as a result of (1) change in the flow field by cutting the dikes built up during lake reclamation and (2) decrease in benthic oxygen consumption by filling up deep holes once created by dredging activities. An erratum to this article is available at .     

Genotypic diversity and structure of Satureja mutica revealed by inter-simple sequence repeat markers

Satureja mutica (Lamiaceae) is an herbaceous medicinal plant which grows in Iran. The objective of the study was to obtain an overview of the genetic relatedness among and within seven populations of this species using inter-simple sequence repeat (ISSR). Fourteen ISSR primers amplified a total of 197 DNA fragments of which 176 (88.91%) were polymorphic. All ISSR primers were highly effective in discriminating among the populations. Genetic similarity coefficients ranged from 0.45 to 0.94, indicating considerable distance and diversity in the germplasm and were confirmed by clustering analysis. The dendrogram showed a clear clustering pattern of plants indicating a significant association between genetic similarity and geographical distance. Analysis of molecular variance revealed that a greater proportion of total genetic variation existed within populations (75%) rather than among populations (25%). The study indicated that ISSR markers were effective and reliable for assessing the degree of genetic variation of S. mutica. These findings can support future research on the selection of S. mutica for breeding and medicinal plant development.     

Population structure and genetic heterogeneity in the Upper Markham Valley of New Guinea.

An analysis is presented of the standardized Wahlund's variances (f) in gene frequencies of the ABO, Rh and MNS blood group systems among 19 villages of the Atsera isolate of the upper Markham Valley, Papua New Guinea. In the past, there has been some disagreement over the relative importance of population structure and natural selection in the determination of these variances. The Lewontin-Krakauer test is presented as a means of resolving this disagreement. According to this test, selectively neutral variation in gene frequencies should generate essentially homogeneous values of f for all loci, a homogeneity which can be tested by comparing the value of (formula: see text) to a theoretical (formula: see text) expected when variations in (formula: see text) are due solely to sampling error. The observed value of (formula: see text) for the Atsera isolate is 2.9 x 10(-5), which is not significantly different from the expected values that range from 1.23 x 10(-5) to 2.46 x 10(-5) depending on the constant used in calculating (formula: see text). Therefore it appears that nonselective aspects of population structure such as genetic drift and intervillage migration are responsible for the recorded genetic variation in this isolate.     

Ecological restoration and factors regulating phytoplankton community in a hypertrophic shallow lake,Lake Taihu,China

A restoration program for the control of cyanobacterial blooms and the re-establishment of submerged macrophytes was conducted in Meiliang Bay of Lake Taihu since 2003. The effect of this ecological projects on plankton community and water quality, and factors regulating phytoplankton community were investigated in 2005. In general, some improvements of water quality occurred in the ecological restoration region, especially in the region of restoring aquatic macrophytes, where we detected significant reduction of nutrients. However, it seems the abundance of phytoplankton cannot be effectively control by the present ecological engineering. The phytoplankton abundance was high in the target restoration zone. Results of CCA and correlation analysis indicate that the phytoplankton community was mainly controlled by physico-chemical factors. Cyanobacteria species were positively related with pH, temperature, TP and TSS, while negatively related with TN, TN/TP and conductivity. The most discriminant variable was TN/TP, which explained 15% of the total variance of phytoplankton. However, TN was more important for the fluctuation of TN/TP than TP. It suggested that TN may be the ultimate factor controlling the phytoplankton community in Lake Taihu. Variation partitioning analysis showed that the pure contribution of crustacean was low for the variation of phytoplankton, suggesting that top-down control by crustacean zooplankton was weak in Lake Taihu. In general, this study suggested the reduction of nutrient load should be more important than top-down control using zooplankton for the ecosystem restoration in Lake Taihu.     

基于rDNA ITS序列分析莲塘湖萼花臂尾轮虫种群遗传结构的季节变化

对采自芜湖市莲塘湖水体中的萼花臂尾轮虫(Brachionus calyciflorus)夏季种群中的30个克隆(S1-S30)和秋季种群中的20个克隆(A1-A20)的rDNA ITS序列进行了分析;以十指臂尾轮虫B.patulus为外群,构建了50个克隆的NJ、MP和ME系统发生树。结果表明:三个系统树均支持将50个克隆分为两个支系;第一支系包括29个夏季采集的单元型(单元型S9除外)和1个秋季采集的单元型A2,第二个支系包括18个秋季采集的单元型(单元型A2除外)和1个夏季采集的单元型S9;两支系间ITS序列差异为5.1%-8.8%;它们应属于两个不同的姐妹种。夏季,莲塘湖水体中的萼花臂尾轮虫种复合体内以第一支系为主构成的姐妹种在相对丰度上占绝对优势,达29/30;而秋季则相反。上述结果表明:浅水湖泊中萼花臂尾轮虫种群密度的季节变动实际上主要在于各姐妹种相对丰度的季节变化;两姐妹种的种群遗传结构季节变化符合重叠模型。     

Population genetic structure of Nantucket pine tip moth

Summary Variation at polymorphic isozyme loci was analyzed in Nantucket pine tip moth (NPTM) populations from 5 geographic locations. At the North Carolina location, populations representing 3 generations at 3 local sites were also studied. Four of the loci investigated (LAP, MDH, -GPDH and AK), although variable, had few alleles per locus (3–5) and few differences among populations in allele frequencies. At each locus, all populations had the same allele at a high frequency.At the PGM locus, fifteen alleles were identified and allelic frequencies varied among populations. At least eight alleles were present within a population and, in most populations, two or more alleles had high frequencies that differed among populations. An excess of homozygotes over Hardy-Weinberg expectations was found for 7 out of the 10 populations studied, indicating the probable existence of some form of inbreeding structure or populational subdivision within sampled stands.Joint consideration of the results observed for PGM and the other four loci is counterindicative of neutrality at all loci and strongly indicative of genetic differentiation among locally disjunct populations.Published as Paper No. 6751 of the Journal Series of the North Carolina Agricultural Research Service     

Population genetic structure of the ascidian Styela rustica at Kongsfjorden, Svalbard, Arctic

The actual Arctic biota shows a strong affinity with that of the Boreal Atlantic and Pacific ones, as a result of an active recolonization process after the Quaternary glaciations. The geographic distribution of sessile species is usually linked to larvae dispersive capabilities which can be directly related with time spent in the plankton. Ascidians larvae are lecitothorphic and short-lived, which suggest that ascidians could be not efficient dispersers. However, the solitary ascidian Styela rustica (Linnaeus, 1767) (Tunicata, Ascidiacea) shows a wide distribution pattern from the North Atlantic to the Arctic that, together with the relatively recent colonization of the Arctic system could indicate that this species efficiently disperses and colonizes new habitats. In this study we used ISSR-PCR markers to study the genetic structure of five populations of the ascidian Styela rustica at Kongsfjorden, west Spitsbergen (Svalbard archipelago). We analyzed whether this species presents a low genetic structure, as can be expected due to the historical process of recent post glaciations colonization, or if there is genetic differentiation at a local scale, caused by short-lived larvae and limited dispersal potential. The genetic diversity in each population assessed using the marker diversity index (M) ranged from 0.288 to 0.324. Population HN, situated close to a fast retreating glacier, showed the lowest diversity. Processes associated with deglatiation (icebergs calving from the glacier that scour the benthos and the increment of inorganic particulate matter on the water column) would drive to reduced population sizes and explain the reduced genetic variability observed in the HN population with respect to the others in the fjord. This suggests a possible linkage with the global warming process. Although the weak genetic structure found among the studied populations could indicate a founder effect, the genetic landscape shape analysis together with a positive relationship between genetic and geographic distances also suggest possible current gene flow among populations in the fjord.     

Population genetic structure of Yushania niitakayamensis (Bambusoideae, Poaceae) in Taiwan

Yushania niitakayamensis is distributed in Taiwan, south-west China and northern Philippines. In Taiwan, the species occurs in the central mountain ranges from 1500 to 3500 m in altitude. Morphological variation, especially in terms of plant height, is large, with plants ranging from 10 cm to 5 m in height. The species appears to spread mainly by rhizomes and flowers rarely, leading to the prediction that most populations are comprised of a single or a few clonal genotypes and that the observed morphological variation is primarily due to phenotypic plasticity. The purpose of the present study was to investigate the genetic structure of this species on Mt Hohuan in central Taiwan. Ten plants from a single clone and ten plants of unknown genetic background were surveyed at one site in order to select RAPD primers useful for clone identification. Plants at a second site were collected at 1-m intervals across a 50-m transect through the population. Plants at one extreme (exposed portion) of the transect were approximately 15–30 cm in height, whereas plants up to 410 cm in height were found at the other shaded end of the transect. Comparison of amplification profiles for 12 primers revealed that in contrast to our predictions of genetic uniformity, many samples had reproducibly different RAPD amplification profiles, with the 51 samples representing 31 clones. These data imply that the clone size is relatively small, and the population is actually highly diverse genetically. The genetic variation in this population may be due to a higher frequency of sexual reproduction during the evolutionary history of the species and/or a high somatic mutation rate for RAPD loci in clones of Yushania.     

Species-Specific Population Structure in Rock-Specialized Sympatric Cichlid Species in Lake Tanganyika,East Africa

Species richness and geographical phenotypic variation in East African lacustrine cichlids are often correlated with ecological specializations and limited dispersal. This study compares mitochondrial and microsatellite genetic diversity and structure among three sympatric rock-dwelling cichlids of Lake Tanganyika, Eretmodus cyanostictus, Tropheus moorii, and Ophthalmotilapia ventralis. The species represent three endemic, phylogenetically distinct tribes (Eretmodini, Tropheini, and Ectodini), and display divergent ecomorphological and behavioral specialization. Sample locations span both continuous, rocky shoreline and a potential dispersal barrier in the form of a muddy bay. High genetic diversity and population differentiation were detected in T. moorii and E. cyanostictus, whereas much lower variation and structure were found in O. ventralis. In particular, while a 7-km-wide muddy bay curtails dispersal in all three species to a similar extent, gene flow along mostly continuous habitat appeared to be controlled by distance in E. cyanostictus, further restricted by site philopatry and/or minor habitat discontinuities in T. moorii, and unrestrained in O. ventralis. In contrast to the general pattern of high gene flow along continuous shorelines in rock-dwelling cichlids of Lake Malawi, our study identifies differences in population structure among stenotopic Lake Tanganyika species. The amount of genetic differentiation among populations was not related to the degree of geographical variation of body color, especially since more phenotypic variation is observed in O. ventralis than in the genetically highly structured E. cyanostictus. [Reviewing Editor: Dr. Rafael Zardoya]