GENETIC VARIATION IN SYMPATRIC AND ALLOPATRIC POPULATIONS OF HYBRIDIZING FRESHWATER SNAIL SPECIES(VIVIPARUS ATER AND V. CONTECTUS)

To estimate the geographical extent of introgression, we studiedthe genetic structure of sympatric and allopatric populationsof hybridizing freshwater snail species Viviparus ater and V.contectus in central Europe. Six allozyme loci which were variablein Lake Garda, Italy in a previous study (five nearly diagnosticloci between the two species and one highly polymorphic locusin V. contectus) were analyzed from ten sympatric locationsand four allopatric populations each for the two species. Presumablyintrogressed genes (low allele frequencies) were found fromat least one locus in seven out of the ten sympatric sites.These seven sites covered most of northern Italy. The data indicatethat introgression has occurred from Viviparus contectus toV. ater and vice versa. Therefore, there is a possibility ofwidespread introgression or mosaic zones in nature. However,we cannot rule out that the observed patterns are due to theshared ancestry. V. ater possessed low genetic variation (thejackknifed mean of Wright's F_ST±S.E. over four loci was0.041±0.004). On the other hand, V. contectus showedhigh genetic differentiation (the jackknifed mean of F_ST±S.E. over six loci was 0.546±0.166). Although introgressionmay have caused evolutionary changes in V. ater and V. contectus,it was not strong enough to level out the genetic differencesbetween the two species, which may have originated from isolationamong populations in V. contectus and a past bottleneck eventin V. ater. (Received 21 June 1996; accepted 31 January 1997)     

RANDOM AMPLIFIED POLYMORPHIC DNA (RAPD) MARKERS REVEAL CROSS-FERTILISATION IN BIOMPHALARIA GLABRATA (PULMONATA: BASOMMATOPHORA)

The freshwater, schistosome-transmitting snail, Biomphalariaglabrata is a simultaneous hermaphrodite which can reproduceby both cross-and selffertilisation, but despite the medicalimportance of this species, little is known about the matingstrategies adopted by wild-type individuals from natural populations.The identification of cross-fertilised progeny is a prerequisitefor both evolutionary studies of the relative fitness of differentreproductive strategies, and for the production of exclusivelyoutcrossed F₁ populations for genetic mapping of biologicallyimportant phenotypes, most notably, resistance to schistosomeinfection. In this study, parents, offspring and ‘syntheticoffspring’ (controls) from four families of B. glabratarecently derived from wild populations were analysed using theRandom Amplified Polymorphic DNA (RAPD) assay. RAPDs were usedbecause they reveal more genetic variation, require less tissue(juvenile snails were only 4–5 mm diameter) than proteinelectrophoresis, are less laborious than other molecular analyses,and do not require sequence data. Seven of the 19 arbitrarysequence, oligonucleotide primers used gave bands that werepolymorophic between pairs of parent snails. Scoring the offspringfor the presence/absence of these polymorphic bands showed thatall the offspring tested were the products of cross-fertilisation.This study provides the first demonstration of the applicabilityof the RAPD technique to an analysis of fertilisation in wild-typeB. glabrata. (Received 20 December 1994; accepted 27 March 1995)     

SURFACING AND WATER LEAVING BEHAVIOUR OF THE FRESHWATER PULMONATE SNAILS LYMNAEA PEREGRA (MULLER), BIOMPHALARIA GLABRATA (SAY) AND BULINUS JOUSSEAUMEI (DAUTZENBERG)

Surfacing and water-leaving behaviour (quitting) of aquaticpulmonate snails was investigated in the laboratory. Regressioncoefficients of surfacing rate per hour for 16 snails in 200cm³ of water were 1.28 for L. peregra, 1.35 for B. glabrata(albino form), 0.47 for B. glabrata (pigmented form) and 0.17for B. jousseaumei. Disturbance, snail size and conditioningof the water were relatively unimportant factors; water volumeadjusted by depth was also unimportant up to 50 mm depth. Importantfactors controlling surfacing appeared to be population density,time of year, temperature, water volume adjusted by perimeterand dissolved oxygen concentration. The response to the latterwas not clear and both B. glabrata and L. peregra orientatedalmost as well to a nitrogen/water interface as to an air/waterinterface. Water-quitting regressed on volume, which had beenadjusted by perimeter variation, revealed a curvilinear relationshipfor B. glabrata, with maximum quitting at 1 snail per 7cm³ (1snail per 14cm of climbable perimeter). L. peregra showed anegative exponential curve, with maximum quitting at 1 snailper 3 cm³ of water (1 snail per 8 cm of climbable perimeter).These data could be relevant to design and management of irrigationchannels where bilharzia might occur. (Received 28 November 1990; accepted 22 October 1991)     

中国桃蛀螟不同地理种群的遗传多样性

本文应用ISSR分子标记技术对中国桃蛀螟Conogethes punctiferalis 11个地理种群的基因组DNA进行了遗传多样性和遗传分化分析。从34条引物中筛选出6条用于ISSR多态性分析, 共扩增出211条带, 其中209条具多态性, 总的多态性条带百分率为99.05%。11个种群的遗传距离在0.0059~0.0237之间, Nei氏基因多样性指数为0.1750, Shannon信息指数为0.2966, 遗传分化系数为0.053, 基因流高达8.8724。结果提示中国桃蛀螟地理种群因基因流水平较高而种群遗传分化水平保持较低。     

Gene flow between populations of two invertebrates in springs

1. Using allozymes, we analysed genetic structure of the freshwater gastropod Bythinella dunkeri and the freshwater flatworm Crenobia alpina. The two species are habitat specialists, living almost exclusively in springs. The sampled area in Hesse (Germany) covers a spatial scale of 20 km and includes two river drainages. From the biology of the two species we expected little dispersal along rivers. However, the possibility exists that groundwater provide suitable pathways for dispersal. 2. In B. dunkeri heterozygosity decreased from west to east. For some alleles we found clines in this geographic direction. These clines generated a positive correlation between geographic distance and genetic differentiation. Furthermore patterns of genetic variation within populations suggested that populations may have been faced with bottlenecks and founder effects. If populations are not in population genetic equilibrium, such founder effects would also explain the rather high amount of genetic differentiation between populations (10%). 3. For C. alpina the mean number of alleles decreased with increasing isolation of populations. Genetic differentiation between populations contributed 19% to the total genetic variation. Genetic differentiation was not correlated to geographic distance, but compared with B. dunkeri variability of pairwise differentiation between pairs of populations was higher in C. alpina. 4. Overall B. dunkeri appears to be a fairly good disperser, which may use groundwater as dispersal pathway. Furthermore populations seem to be not in equilibrium. In contrast C. alpina forms rather isolated populations with little dispersal between springs and groundwater seems to play no important role for dispersal.     

HABITAT CONSTRAINTS ON SHELL-COLOUR VARIATION OF A DESERT LANDSNAIL, TROCHOIDEA SIMULATA

Trochoidea simulata, a landsnail widespread in desert regionsof Israel, varies greatly in shell colour. We have previouslyshown that predator and thermoegulatory mediated selection cannotexplain the maintenance of this colour variation. In this paper,we test the hypothesis that observed morph frequencies are aneffect of habitat variation, and that the colour variation hasno functional significance. Because white snails have thickershells than striped or brown snails, we propose that the colourof an individual snail depends on its access to CaCO₃. We testedthis hypothesis by comparing the frequency of white, striped,and brown snails at 9 locations. Each location consisted ofa paired hillside and loess wadi-bed site with high and lowCaCO₃ content respectively. There were significantly more whitesnails at hillside than loess sites. In addition, these habitatsvaried mostly in abiotic characteristics, and not in terms ofsnail population parameters or vegetation characteristics. Hillsidesites had significantly more CaCO₃ and limestone rocks thanloess sites. Soil CaCO₃ content was the strongest predictorof morph frequency among paired sites. Shell-colour variationin this species may be an effect of individual access to resources,mainly CaCO₃ that is ingested with food. (Received 5 August 1996; accepted 25 October 1996)     

Strong genetic differentiation due to multiple founder events during a recent range expansion of an introduced wall lizard population

Biological invasions represent ideal systems for the study of evolutionary processes associated with colonization events. It has been hypothesized that the genetic diversity is generally decreasing from the centre of the range to the margins due to multiple founder events. Invasive populations offer the opportunity to test this hypothesis at a fine spatial and temporal scale. We analysed the genetic structure of a large expanding non-native population of the Common Wall Lizard (Podarcis muralis) in Passau (Germany) using thirteen microsatellite loci. We analyzed the genetic structure and levels of admixture across a transect reflecting the expansion process and tested for a loss of genetic diversity and an increase of genetic differentiation from the centre to the invasion front. Our results demonstrate that significant genetic population structure can emerge rapidly at a small spatial scale. We found a trend for an increase in genetic differentiation and a decrease in genetic diversity from the invasion centre to the expanding range margin, suggesting that genetic drift is the major factor causing this pattern. The correlation between genetic diversity and average genetic differentiation was significant among sites. We hypothesize that the territoriality of P. muralis generates sufficient rates of noncontiguous and stratified dispersal from longer established sites to maintain significant genetic diversity at the invasion front. Simultaneously, territoriality might restrict the colonization success of migrants at established sites, so that in combination with founder events a strong differentiation arises.     

中国桔小实蝇种群的微卫星多态性分析

为了研究桔小实蝇种群的遗传结构,本文采用微卫星分子标记技术,对中国南方9省区、越南和泰国的11个桔小实蝇地理种群共224个个体的遗传多样性水平及种群遗传结构进行了研究。用9对微卫星引物共检测到48个等位基因, 平均每个微卫星位点的等位基因数为5.33个。GENEPOP分析结果表明：11个桔小实蝇种群在9个微卫星位点上的多态位点百分率平均为94.45%。种群的Nei's基因多样性指数平均为0.4371,Shannon信息指数平均为0.7870,表明桔小实蝇种群具有非常丰富的遗传多样性。Nei's遗传多样性分析发现,各地理种群间产生了一定程度的遗传分化,种群间平均遗传分化系数F_st=0.2370。种群间一定程度的遗传分化可能是由地理隔离和基因流障碍（N_em = 0.8049）所引起。UPGMA聚类分析可知, 中国的桔小实蝇地理种群可分为华南支和西南支两大分支,华南分支包括福建、台湾、广东和海南4个种群,西南分支包括四川、云南、广西、贵州和湖南5个种群。由此推测, 中国桔小实蝇种群结构的形成与演变是在地理演化与经贸交流加强这两种因素的影响下不断进行的动态过程。     

ASPECTS OF LIFE CYCLE, POPULATION DYNAMICS, GROWTH AND SECONDARY PRODUCTION OF THE PULMONATE SNAIL CEPAEA VINDOBONENSIS (FERUSSAC, 1821) IN NORTHERN GREECE

The life cycle, population dynamics, growth and secondary productionof the land snail C. vindobonensis were studied in northernGreece. Demographic analysis of the populations of C. vindobonensisrevealed that a) three cohorts were present in the field throughoutthe year, b) the reproductive period started in late April-Mayand the newly hatched snails appeared in the beginning of June,and c) increased growth rates were observed during spring andearly summer, but also during autumn for the newly hatched snails. According to von Bertalanffy's method C. vindobonensis needs7 years to attain its maximum size measured in the field. Mortalityrate is very high during the first year of life, while lifeexpectancy is higher during the second year of life and decreasesafterwards. Net reproductive rate (R_o) was equal to 3.1 andthe finite capacity for increase (antilog_er_c) was equal to 1. Estimated annual secondary production with Hynes' frequencymethod revealed a mean standing crop (B) of 0.99 g/m²/year anda production (P) of 1.3 ± 0.11 g/m²/year. Annual turnoverratio (P/B) was equal to 1.31. (Received 7 April 1997; accepted 2 October 1997)     

突尼斯非洲跳鼠(Jaculus jaculus)和埃及跳鼠(J.orientalis)群体的等位酶多态及遗传分化(英文)

运用16种酶蛋白编码的23个遗传座位对突尼斯非洲跳鼠(Jaculus jaculus)和埃及跳鼠(J. orientalis)自然群体的遗传变异和分化进行了电泳分析。结果表明,与其他啮齿动物等哺乳动物的相关数据比较,发现这两个种群体的遗传变异水平较低。非洲跳鼠群体的观测杂合度 (H_obs) 为0.08—0.19,多态座位百分比(P)为26.2%—45.2%,每个座位的平均等位基因数(A)为1.1—1.4;埃及跳鼠的H_obs为0.10—0.15,P为29.3%—44.1%,A为1.1—1.7。两个种群体各自的遗传分化程度较低(非洲跳鼠和埃及跳鼠的F_st分别为0.0017和0.0019)。而两个种群体间的F_st为0.607（P<0.05）,表明两个种之间高度的遗传分化。本研究支持这两个种分类地位的合法性,并强调了地理因素（环境类型和生物气候阶段）对两个种遗传结构的影响。     

Superfluous killing in spiders: a consequence of adaptation to food-limited environments?

The hypothesis that superfluous killing, partial consumption,and abandonment of prey is a consequence of adaptation to food-limited environments was tested in two feeding trials on a desert spider, Agelenopsis aperta. First, we made comparisons among populations inhabiting sites of high prey (HP) or low prey (LP) availabilitythat differed in their degree of genetic isolation. Typically,A. aperta entirely consumed one or two of the prey items itcaptured in a feeding bout. Additional prey were partiallyconsumed or abandoned without eating. Spiders from the geneticallyisolated HP population, however, captured fewer prey and showeda higher incidence of full feeding on prey than did individualsfrom the other populations. Only one spider from this populationcaptured a prey item that it failed to feed on, whereas spidersfrom LP populations failed to feed on high numbers of capturedprey. The greatest variability in feeding behavior was exhibitedin the HP population that experienced gene flow. The secondtest was based on the finding that aggressiveness is largelya sex-linked trait in A. aperta: the aggressiveness of thefemale parent only is inherited by male offspring, whereasboth parents contribute to this trait in female offspring.All female F₁ hybrids between LP and HP parental types exhibitedhigh levels of superfluous killing, as did male F₁ hybridsderived from LP females. F₁ hybrid males derived from HP femalesexhibited extremely low levels of superfluous killing. Superfluouskilling thus has its basis in the genetic control of levelsof aggression.     

Local Differentiation Among Populations of Arabis stelleri var. japonica in a Sand Dune Habitat

Local variation in ecological and genetic traits was analysedin the perennial herb Arabis stelleri var. japonica in a sanddune area in western Japan. Plants of this species are establishedin three contiguous habitats (subpopulations): sand dune, forestand an ecotonal zone between both habitats. Morphological, ecologicaland genetic traits of A. stelleri var. japonica plants wereanalysed to discover the extent of microdifferentiation amongthese subpopulations. All plants in nine quadrats were markedand followed during 2 years. The ecotonal zone presented thehighest number of mature individuals per quadrat. Plants mayproduce the same number of shoots per plant but rosette sizewas larger in plants from sand dune and forest subpopulationsthan the ecotone. Plants in the sand dune showed the highestnumber of large capsules per plant. Mortality of seedlings andmature plants was slightly higher in the ecotone than in theother two subpopulations. Sand dune plants had the highest variationamong quadrats in almost all traits measured. In the electrophoreticanalyses, 21 loci were detected on twelve enzyme systems. Fifteenloci were monomorphic and six loci had 1·2 alleles perloci. Genetic distances and genetic identity Nei's values werevery similar among subpopulations (means I = 0·994, D= 0·006). The total genetic diversity (H_T) was 0·340and the within-population component (H_s) was 0·333 indicatinglow genetic differentiation among subpopulations. Gene flowvaried between genes but most of the values were high (meanNm = 188·3). Subpopulations of A. stelleri showed differentiationin morphological and ecological traits and low genetic differentiationin the loci studied. This may be related with the plastic responseof plants to different microenvironments and a significant geneflow between habitats.Copyright 1994, 1999 Academic Press Arabis stelleri var. japonica, Brassicaceae, gene flow, genetic diversity, local differentiation, mortality, plant population, reproduction     

Decline of a sylvatic focus of Schistosoma mansoni in Guadeloupe (French West Indies) following the competitive displacement of the snail host Biomphalaria glabrata by Ampullaria glauca

Summary Grand Etang lake in Guadeloupe is a focus of intestinal schistosomiasis characterized by the virtual absence of human contact and the presence of a heavily infested rat population. The lake, with a surface area of 0.03 km², is situated in rain forest at an altitude of 450 m. Originally it contained an extensive belt of the floating plant Pistia stratiotes which provided a favourable habitat for Biomphalaria glabrata, the intermediate host snail of Schistosoma mansoni. In 1974 and 1975, a low prevalence (about 3%) of S. mansoni was observed in B. glabrata while a high prevalence (about 60%) was recorded in rats. The rat population was infected with another trematode, Ribeiroia guadeloupensis, which requires two intermediate hosts, B. glabrata and the fish Tilapia mossambica. In 1976, the prosobranch snail, Ampullaria glauca, was accidentally introduced into the lake. By 1980, this snail had spread over half of the lake and had caused marked regression of the P. stratiotes layer. Concomitantly, the population of B. glabrata declined to such a point that in 1985 only a small colony remained in the northern section of the lake. The consequences of these changes are reflected in a rapid decline of S. mansoni in the rat population from 61.3% in 1980 to 34.8% in 1981, 6.5% in 1982, 2.8% in 1983, 11.6% in 1984, and 0% in 1985 and 1986.     

Role of Coccoliths in the Utilization of Inorganic Carbon by a Marine Unicellular Coccolithophorid, Emiliania huxleyi: a Survey Using Intact Cells and Protoplasts

The utilization of inorganic carbon and role of the coccolithswere investigated in intact cells and protoplasts of a marineunicellular calcareous alga, Emiliania huxleyi. Protoplastswith high photosynthetic activity were obtained by artificialdecalcification with 50 mM MES-NaOH (pH5.5). (1) The kineticsof the photosynthetic evolution of O₂ at various concentrationsof externally added NaHCO₃ were the same for intact cells andprotoplasts, indicating that the kinetic properties with respectto dissolved inorganic carbon (DIC) were not affected by thepresence or absence of the coccoliths on the cell surface. Double-reciprocalplots and plots of the concentration of substrate divided byvelocity (s/v) against the concentration of substrate (s) werebiphasic in the case of both intact cells and protoplasts. TheCO₂-utilization reaction was, therefore, considered to involvetwo processes with different values of K_m and V_max. From thekinetic analyses, K_m and V_max [µmoles O₂ (ml PCV)^–1h^–1] were deduced to be 92 µM and 76.3 for a "low-K_m"reaction and 4.1 mM and 252 for a "high-K_m" reaction, respectively.(2) In short-term (40-min) experiments, time courses of thetotal uptake of ¹⁴C-DIC and the incorporation of ¹⁴C into acid-stableproducts of photosynthesis and the internal pool of DIC, determinedas acid-labile compounds, under CO₂-limiting conditions (80µM) were very similar for intact cells and protoplasts.However, incorporation of ¹⁴C into CaCO₃ apparently occurredmore slowly in protoplasts than in intact cells. (3) In longterm (24-h) experiments, patterns of incorporation of ¹⁴C werealmost same for intact cells and protoplasts, with the exceptionthat the amount of ¹⁴C incorporated into CaCO₃ was much smallerin the former than the latter. The production of Ca¹⁴CO₃ increasedduring the course of 10 h after a 4-h lag. However, after 10h the level of Ca¹⁴CCO₃ started to decrease. The decrease wasaccompanied by an increase in ¹⁴C in the products of photosynthesis,suggesting that CaCO₃ was reutilized for the photosyntheticfixation of CO₂ and, therefore, that the coccoliths functionas sites of storage of DIC. However, the internal level of DICremained at the same level even after the supply of externalDIC has been almost completely depleted. (Received July 25, 1995; Accepted December 11, 1995)     

Mate choice, frequency dependence, and the maintenance of resistance to parasitism in a simultaneous hermaphrodite

Biomphalaria glabrata are simultaneous hermaphroditic freshwatersnails that act as intermediate hosts for the macroparasitictrematode Schistosoma mansoni, a causative agent of schistosomiasis.Heritability and strain-specificity of both snail resistanceand susceptibility to schistosome infection have been demonstrated,genetic variability for which is maintained, in part, throughtrade-offs between high fitness costs associated with infectionand those associated with resistance. However, despite sucha high cost of resistance and a low prevalence of infectionin natural snail populations, genes for resistance are maintainedwithin snail populations over successive generations, includingin the complete absence of parasite pressure in laboratory populations.This may be indicative of alternative benefits of resistancegenes, in addition to parasite defense, such as differentialmating success between genotypes. Here we examined the mateand gender choice of snails across a multi-factorial range ofpotential partner combinations. These included host-resistanceor susceptibility genotype, host genotype frequency within thepopulation, current parasite infection status, and parasitegenotype. We demonstrate recognition and discrimination by hostsnails depending on host and/or parasite genotype for each ofthese factors. In particular, our results suggest that a raremating advantage to resistant genotypes may be a potential explanationfor the maintenance of highly costly resistance genes withinintermediate host populations under conditions of low or zeroparasite pressure.     

DEVELOPMENT OF ACCESSORY SEXUAL ORGANS IN BIOMPHALARIA GLABRATA (PLANORBIDAE) IN RELATION TO TIMING OF INFECTION BY SCHISTOSOMA MANSONI: CONSEQUENCES FOR ENERGY UTILIZATION PATTERNS BY THE PARASITE

The growth rates of ovotestis and individual accessory sexualorgans (ASO) of Biomphalaria glabrata snails were studied forcontrols and for immature and mature snails infected with Schistosomamansoni. The infection of immature B. glabrata strongly delaysgrowth of the ovotestis and inhibits the development of theaccessory sexual organs. There is no significant differenceup to 2 weeks post infection in the volume of the ovotestisand the ASO between mature infected B. glabrata and controlsnails. From 3 to 4 weeks post infection there was a reductionin the volume of the ovotestis and the ASO of infected matureB. glabrata; then growth of the ovotestis, albumen gland andfemale organs was stopped, but the effect of infection was lessconsistent for the male organs. For a parasite, immature andmature snails have to be considered as two different resourceenvironments, each having at infection time a particular patternof resource allocation, towards growth for juvenile and towardsreproduction for adult snails, changing the possible energyutilization patterns which can be used by the trematode. (Received 29 January 1993; accepted 22 April 1993)     

GENETIC AND MORPHOLOGICAL VARIATION OF POPULATIONS BELONGING TO THE BULINUS TRUNCATUS/TROPICUS COMPLEX (GASTROPODA; PLANORBIDAE) IN SOUTH WESTERN ZIMBABWE

Aquatic snails from south western Zimbabwe belonging to theBulinus trunscatus/tropicus complex vary widely in shell formsuggesting that more than one taxon could be present. This possibilitywas investigated by making observations on snail samples from13 populations from the Plumtree area, in respect of allozymevariation (5 polymorphic loci), shell morphology (9 variables),copulatory organ and chromosome number. Comparative data wereobtained from snails from north western Zimbabwe identifieddefinitely as B. tropicus. Analysis of the genetic structurerevealed a high degree of polymorphism (P) ranging from 0.29–0.80among populations from Plumtree and expected heterozygosity(H_e) from 0.02–0.22. No enzymatic diagnostic loci werefound which could differentiate the different morphs or populationsand discriminant function analysis on the morphological datashowed an overlap of morphs among populations. Snails analyzedfor chromosome number were all diploid (2n = 36). Snails exposedto Schistosoma haematobium mira-cidia were all refractory. Thisinformation supports the view of a single species, B. tropicus,which is differentiated due to migration barriers and whereenvironmental variables might be implicated in the morphometricdivergence. (Received 31 July 1995; accepted 15 January 1998)     

Stereological Analysis of Floral Development and Quantitative Histochemistry of Nucleic Acids in Fertile and Base-sterile Varieties of Wheat

The speltoid series of mutations provides a genetic tool forinvestigating the control of flower development. In fertileGabo wheat and in St₂ and St₃ basal sterile speltoids, the changesin RNA staining patterns have been followed histochemicallyas a marker of cellular activity. Sterile floret sites are characterizedby a reduced RNA content. Use of dual-wavelength microspectrophotometryhas provided evidence that RNA content is similar in lemma primordiasubtending presumptive fertile and sterile primordia, but isstrikingly different in the floral meristems in the two types.The total nucleic acid content of the floral primordia has beenrelated to the number of epidermal cells in the subtending lemmaprimordium as a marker of development, using a linear modelanalysis of covariance. There is a linear increase in nucleicacid content during fertile floret development, but no significantincrease in RNA content in sterile St₃ primordia. The rate constantis only 1/10th to 1/20th of that of Gabo. A stereological analysisshows that cell number in the floral meristems of Gabo increasesexponentially during development. In contrast, in St₃, whilethere is a significant increase in cell number, it is at a drasticallyreduced rate. The intercept values are close to zero, indicatingthat only one or two cells initiate floral meristem development.The fertility-controlling alleles exert their effect prior tothe appearance of a visible floral primordium, and probablyafter initiation of the lemma. Triticum aestivum, wheat, floral development, histochemistry, nucleic acids, speltoids     

Fine-scale genetic structure among genetic individuals of the clone-forming monotypic genus Echinosophora koreensis (Fabaceae)

• Background and Aims For rare endemics or endangered plantspecies that reproduce both sexually and vegetatively it iscritical to understand the extent of clonality because assessmentof clonal extent and distribution has important ecological andevolutionary consequences with conservation implications. Asurvey was undertaken to understand clonal effects on fine-scalegenetic structure (FSGS) in two populations (one from a disturbedand the other from an undisturbed locality) of Echinosophorakoreensis, an endangered small shrub belonging to a monotypicgenus in central Korea that reproduces both sexually and vegetativelyvia rhizomes. • Methods Using inter-simple sequence repeats (ISSRs) asgenetic markers, the spatial distribution of individuals wasevaluated using Ripley's L(d)-statistics and quantified thespatial scale of clonal spread and spatial distribution of ISSRgenotypes using spatial autocorrelation analysis techniques(join-count statistics and kinship coefficient, F_ij) for totalsamples and samples excluding clones. • Key Results A high degree of differentiation betweenpopulations was observed (_ST(g) = 0·184, P < 0·001).Ripley's L(d)-statistics revealed a near random distributionof individuals in a disturbed population, whereas significantaggregation of individuals was found in an undisturbed site.The join-count statistics revealed that most clones significantlyaggregate at 6-m interplant distance. The Sp statistic reflectingpatterns of correlograms revealed a strong pattern of FSGS forall four data sets (Sp = 0·072–0·154), butthese patterns were not significantly different from each other.At small interplant distances (2 m), however, jackknifed 95% CIs revealed that the total samples exhibited significantlyhigher F_ij values than the same samples excluding clones. • Conclusion The strong FSGS from genets is consistentwith two biological and ecological traits of E. koreensis: bee-pollinationand limited seed dispersal. Furthermore, potential clone matesover repeated generations would contribute to the observed highF_ij values among genets at short distance. To ensure long-termex situ genetic variability of the endangered E. koreensis,individuals located at distances of 10–12 m should becollected across entire populations of E. koreensis.     

Demographic and genetic invasion history of a 9-year-old roadside population of Bunias orientalis L. (Brassicaceae)

The population history of a 9-year-old roadside population of the invasive plant Bunias orientalis was reconstructed by demographic analysis including size, position, age (determined by herbchronology) and RAPD-PCR patterns of individual plants. We evaluated emerging patterns of population growth and genetic structure during a full period of population development under typical site conditions (anthropogenic disturbance) and their possible consequences for the invasion potential of the species. The population has grown rapidly and continuously (though with slowing geometric population increase) during the 9 years since its foundation, filling the space available in the study area. Genetic variation (RAPD markers) was already high in the founder cohorts and remained at the same level throughout population development (variance fluctuations <15%). Both results may be related to the mowing management at the site which seems to promote population growth of B. orientalis relative to other co-occuring species and to prevent the genetic drift and the development of spatial genetic structure that would be expected under isolation-by-distance models. Large founder plants had comparatively low genetic variance and were more closely related to younger cohorts than were small founder plants, indicating that selection acted during population development. Overall, the current anthropogenic disturbance regimes may contribute to high genetic variability by artificially increasing gene flow and thereby promoting the adaptability of invasive species to the often unpredictable conditions at disturbed sites. Our approach using retrospective demographic investigation allows the detection of spatio-temporal microscale patterns in genetic and phenotypic variation. Thus it allows a thorough understanding of local invasions of perennial herbaceous plants. Received: 23 November 1998 / Accepted: 14 April 1999