Evidence for multiple introductions of Centaurea stoebe micranthos (spotted knapweed,Asteraceae) to North America

Invasive species’ success may depend strongly on the genetic resources they maintain through the invasion process. We ask how many introductions have occurred in the North American weed Centaurea stoebe micranthos (Asteraceae), and explore whether genetic diversity and population structure have changed as a result of introduction. We surveyed individuals from 15 European native range sites and 11 North American introduced range sites at six polymorphic microsatellite loci. No significant difference existed in the total number of alleles or in the number of private alleles found in each range. Shannon–Weaver diversity of phenotype frequencies was also not significantly different between the ranges, while expected heterozygosity was significantly higher in the invasive range. Population structure was similar between the native range and the invasive range, and isolation by distance was not significant in either range. Traditional assignment methods did not allocate any North American individuals to the sampled European populations, while Bayesian assignment methods grouped individuals into nine genetic clusters, with three of them shared between North America and Europe. Invasive individuals tended to have genetically admixed profiles, while natives tended to assign more strongly to a single cluster. Many North American individuals share assignment with Romania and Bulgaria, suggesting two separate invasions that have undergone gene flow in North America. Samples from three other invasive range sites were genetically distinct, possibly representing three other unique introductions. Multiple introductions and the maintenance of high genetic diversity through the introduction process may be partially responsible for the invasive success of C. stoebe micranthos.     

The earliest House Sparrow introductions to North America

Several authors have argued that three separate introductions of roughly 100 individuals were required initially to establish the House Sparrow (Passer domesticus) in the Brooklyn, New York area. We argue that these claims are in error and that the actual record suggests that it is likely the initial introduction of just 16 birds in 1851 was all that was required to establish the species in New York. We further suggest that a similar level of scrutiny of historical records will reveal more examples of misinterpretations and errors, casting doubt on the validity of studies that claim propagule pressure has played an important role in determining the fate of bird introductions.     

Susceptibility of native and non-native common reed to the non-native mealy plum aphid (Homoptera: Aphididae) in North America

An aggressive, non-native haplotype (distinct genetic lineage within a species) of Phragmites australis is invading brackish and freshwater systems in the eastern United States, potentially displacing native haplotypes. We studied the differential susceptibility of native and non-native populations collected from sites throughout North America to the non-native aphid, Hyalopterus pruni. In a greenhouse study, we found significantly higher aphid populations on native haplotypes than on the non-native haplotype 2 mo after infestation. Aphid feeding caused chlorosis and death of native stems, and in some cases, killed whole native genets. The non-native plants remained relatively undamaged. In a field study, non-native plants had significantly lower aphid densities than native plants or remained aphid free. There was an interactive effect in which aphid populations increased on the native plants over the 1-mo study period but remained low on non-native plants over the same period. The susceptibility of native North American populations of P. australis to non-native aphid infestation may indirectly affect the ability of these native plants to compete with non-native plant populations, ultimately contributing to the decline of native haplotypes.     

Threat of non-native crayfish introductions into Turkey: global lessons

Introductions of crayfish species from their home range to new environments have been carried out in many parts of the world. The most important introduced crayfish species are Procambarus clarkii, Pacifastacus leniusculus, Cherax destructor, C. quadricarinatus, Orconectes limosus, O. rusticus and Astacus leptodactylus. The environmental impact of crayfish introductions can be positive, negative or neutral. However, native crayfish populations in Europe have been negatively affected by introductions of non-indigenous crayfish species from America. Negative effects of non-native crayfish introductions included displacement of native crayfish species, transfer of disease (crayfish plague), consumption of fish eggs, reduction of fish stocks, consumption of large amounts of macrophytes, indirect and direct effects on other invertebrates and upsetting production in rice fields. As a result of non-native crayfish introductions, the natural harvest and crayfish industry in Europe have been severely affected. Large quantities of Turkish A. leptodactylus were harvested (approximately 7,000 tonnes annually) and exported to Europe before the crayfish plague was observed in these populations. The total harvest of A. leptodactylus in Turkey reduced dramatically to 320 in 1991 after the plague. Therefore, although Turkey currently has no known non-native crayfish species, there is a threat of non-native crayfish introduction in order to increase crayfish productions and subsequent harvest. The North American spiny-cheek crayfish, O. limosus, has been spreading quickly down the River Danube and could soon reach neighboring countries including Turkey. The North American signal crayfish, P. leniusculus is known from Greece and could be a threat to native stocks if it is introduced into Turkey for aquaculture. Additional threats may come from the release of other North American species, which are widely available through the aquarium trade. We conclude that the spread of non-native crayfish introductions throughout Turkey will increase local problems, because introductions of non-native crayfish in many parts of the world have been known to have caused important reductions in population density and numbers of native crayfish species. Furthermore, freshwater ecosystems may be altered by such introductions and the economic viability of native crayfish species fisheries could be severely reduced in Turkey.     

Tolerance and physiological responses of Phragmites australis to water deficit

The water stress tolerance of Phragmites australis (Cav.) Trin ex. Steud. grown in the laboratory were investigated by examining effects of different levels of imposed water deficits on growth, photosynthesis and various physiological traits related to water stress. Individual plants were grown under conditions of unrestricted water supply and compared with groups of plants receiving 60, 30, 15 or 5% of previous daily water requirements, respectively.Water deficit was found to reduce the leaf area and the leaf biomass per plant due to decreased production of new leaves, increased leaf shedding and reduced average leaf size. Leaf production and leaf expansion growth were very sensitive to water availability and were reduced when plants were subjected to fairly mild water deficit. Osmolality in sap expressed from leaves and the concentration of proline in leaves were only significantly increased in severely stressed plants, indicating that osmotic adjustment was of minor importance until a critical stress level was reached. Photosynthetic parameters were rather unaffected until the water availability was very low and led to the assertion that reduced CO₂ assimilation was mainly due to stomatal closure and not biochemical changes. Water stress had no effect on the activity of Rubisco. The CO₂ assimilation rate and stomatal conductance decreased in such a way that the intrinsic water use efficiency (A/g_s) increased, indicating efficient CO₂ utilization in water stressed plants. The apparent quantum yield (φ_i) was reduced in leaves of the most stressed plants, probably due to a decrease in the CO₂ molar fraction in the chloroplasts following stomatal closure.The initial response of P. australis to water deficit is a reduction in leaf area, the remaining leaves staying physiological rather well functioning until they are severely stressed. A high intrinsic water use efficiency and the ability to maintain some capacity for photosynthesis under severe water stress can undoubtedly contribute to the survival of P. australis under dry conditions. Taken together with its well-developed adaptations to flooding, P. australis seems very well adapted to grow in wetland areas with a widely fluctuating hydroperiod. P. australis grows very well in rather deep water, but can also tolerate extensive periods of drought with reduced availability of water.     

Evidence of a physiological basis for the boreal-deciduous forest ecotone in North America

The observed northern limit of the deciduous forest formation in North America is shown to agree closely with the reported –40°C average annual minimum temperature isotherm. This indicates that supercooling as a means of resisting freezing stresses may set a physiological limit on the northern expansion of the deciduous forest formation.Abbreviation LTE= Low Temperature Exotherm     

Evidence for a host-marking pheromone in Chaetorellia australis

Experiments and observations on the oviposition behavior of Chaetorellia australis Hering (Diptera, Tephritidae) females, caged in the laboratory with their natural oviposition substrates, floral buds of the yellow starthistle (YST) Centaurea solstitialis L. and Centaurea cyanus L. (Asteraceae: Cardueae) revealed that females of that species deposit a contact host-marking pheromone immediately after oviposition by dragging their extended ovipositor over the floral bud surface. The function of this pheromone is the prevention of repeated oviposition in already infested oviposition sites. Apparently it also plays a role in sexual behavior by functioning as a male arrestant. The pheromone was found to be soluble in water but insoluble in methanol, ethanol, diethyl ether and acetone. Under laboratory conditions, its effectiveness persisted for at least 10 days. By preventing oviposition on already infested buds the pheromone apparently contributes to uniform egg dispersion among available resources for larval development. By functioning as a male arrestant, which causes aggregations of males on places visited frequently by females such as the floral buds of host plants, it also contributes to overall fertility by facilitating encounters of the sexes. The potential practical application for biocontrol of the YST through introducing and releasing C. australis flies into areas infested by the weed is discussed.

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Zusammenfassung Versuche und Beobachtungen über das Eiablageverhalten von im Labor mit ihren natürlichen Eiablagesubstraten, d.h. Blütenknospen von Centaurea solstitialis L. und Centaurea cyanus L. (Asteraceae: Cardueae) gehaltenen Chaetorellia australis Hering (Diptera: Tephritidae) zeigten, dass C. australis Weibchen sofort nach der Eiablage die Oberfläche der Blütenknospe mit einem eiablageverhindernden Pheromon markieren, indem sie ihren ausgestellten Ovipositor über die Oberfläche der Blütenknospe ziehen. Das Pheromon, das auch als Männchen-Arrestans wirkt, ist wasserlöslich, jedoch unlöslich in Methanol, Äthanol, Diethyläther und Aceton. Unter Laborbedingungen hält seine Wirkung mindestens 10 Tage an. Da das Pheromon die Eiablage an bereits infestierten Blütenknospen verhindert, trägt es zu einer gleichmässigen Eiverteilung in den für die Larvenentwicklung zur Verfügung stehenden Futtequellen bei. Als Männchen arretierendes Pheromon führt es zur Aggregation von Männchen an den Blütenknospen, die oft von Weibchen besucht werden und versichert somit eine hohe Fertilität, indem es das Zusammentreffen der Geschlechter erleichtert. Die praktische Anwendung der Ergebnisse für die biologische Bekämpfung von Centaurea solstitialis durch Einfuhr und Freilassung von C. australis in die mit dem Unkraut verseuchten Gebiete wird diskutiert.

     

A comparison of Phragmites australisin freshwater and brackish marsh environments in North America

This paper compares the available North Americanliterature and data concerning several ecologicalfactors affecting Phragmites australisin inlandfreshwater, tidal fresh, and tidal brackish marshsystems. We compare aboveground productivity, plantspecies diversity, and sediment biogeochemistry; andwe summarize Phragmiteseffects on faunalpopulations in these habitats. These data suggest thatPhragmitesaboveground biomass is higher thanthat of other plant species occurring in the samemarsh system. Available data do not indicate anysignificant difference in the aboveground Phragmitesbiomass between marsh types, nor doesthere appear to be an effect of salinity on height.However, Phragmitesstem density wassignificantly lower in inland non-tidal freshwatermarshes than in tidal marshes, whether fresh orbrackish. Studies of the effects of Phragmiteson plant species richness suggest that Phragmitesdominated sites have lower diversity.Furthermore, Phragmiteseradication infreshwater sites increased plant diversity in allcases. Phragmitesdominated communities appearto have different patterns of nitrogen cyclingcompared to adjacent plant communities. Abovegroundstanding stocks of nitrogen (N) were found to behigher in Phragmitessites compared to thosewithout Phragmites. Porewater ammonium(NH₄ ⁺) did not differ among plant covertypes in the freshwater tidal wetlands, but inbrackish marshes NH₄ ⁺was much higher inSpartinaspp. than in neighboring Phragmitesstands. Faunal uses of Phragmitesdominated sites in North America were found to vary bytaxa and in some cases equaled or exceeded use ofother robust emergent plant communities. In light ofthese findings, we make recommendations for futureresearch.     

Physiological responses of Phragmites australis to wastewater with different chemical oxygen demands

Constructed wetlands have been widely used to treat various wastewaters with large differences in their concentration of pollutants. The capability of wetland plants to resist these wastewaters is crucial for a wetland's healthy development. Phragmites australis has been shown to have the capability to grow in simulated wastewater containing a wide concentration of pollutants. In this study, the physiological responses of P. australis to simulated wastewaters with high chemical oxygen demands (CODs) were investigated in a bucket experiment. P. australis was incubated in buckets for 30 days at five treatments of 0, 100, 200, 400, and 800 mg L^?1 COD simulated wastewater. The net photosynthesis rate of the plants declined markedly with increasing COD levels. Proline and malondialdehyde (MDA) contents also increased dramatically. The plants further showed a unimodal pattern of superoxide dismutase (SOD) and peroxidase (POD) distribution along external COD values on the whole, indicating that high COD values (≥200 mg L^?1) can disrupt the normal metabolism of the plant. High COD levels (COD ≥ 400 mg L^?1) caused evident physiological changes in P. australis.     

Shoreline processes and establishment of Phragmites australis in a coastal plain estuary

Phragmites australis occurs extensively along undisturbed salt-marsh shorelines of Delaware Bay. The species has been considered indicative of human disturbance when found in estuarine marshes in the USA. It is suggested that geomorphic processes associated with coastal submergence provide an analog of human disturbances which can enable Phragmites australis to become established naturally. Deposition of sand bodies (or rafted debris) can suppress existing vegetation and allow Phragmites to become established. Subsequently, even if the sand or debris is moved, erosional truncation of the intertidal profile can inhibit recolonization by the original dominant shoreline species, Spartina alterniflora.     

Genetic divergence between North American ancestral soybean lines and introductions with resistance to soybean cyst nematode revealed by chloroplast haplotype

Domesticated soybean [Glycine max (L.) Merr.] is a major crop with an established ancestral relationship to wild soybean (Glycine soja Sieb. & Zucc.) native to Asia. Soybean genetic diversity can be assessed at different levels by identification of polymorphic alleles at genetic loci, in either the plastid or nuclear genomes. The objective of this study was to evaluate genetic diversity based on chloroplast haplotypes for soybean genotypes present in the USDA germplasm resource collection. Shared chloroplast haplotypes represent broad groups of genetic relatedness. Previous work categorized three-quarters of the cultivated soybeans from Asia into a single haplotype group. Our results confirmed the close relationship of North American soybean ancestors and G. max plant introductions previously identified as representing potential sources of soybean genetic variation with the finding that these genotypes belonged to a single chloroplast haplotype group. Genetic diversity was identified in soybean genotypes determined to have a high density of single nucleotide polymorphisms and in a screen of accessions with resistance to soybean cyst nematode. Characterization of soybean plant introduction lines into chloroplast haplotype group may be an important initial step in evaluating the appropriate use of particular soybean genotypes.     

干旱区湿地芦苇各器官生态化学计量对土壤因子的响应

了解植物养分浓度及其化学计量对土壤因子的响应,对预测脆弱而敏感生态系统对环境变化的响应至关重要.以敦煌阳关湿地优势种芦苇(Phragmites australis)为对象,通过野外调查与实验分析,研究芦苇不同器官生态化学计量特征及其影响因素.结果 表明:芦苇各器官C、P含量为叶＞根＞茎,N含量及N∶P为叶＞茎＞根,C∶...     

Zinc isotopic fractionation in Phragmites australis in response to toxic levels of zinc

Stable isotope signatures of Zn have shown great promise in elucidating changes in uptake and translocation mechanisms of this metal in plants during environmental changes. Here this potential was tested by investigating the effect of high Zn concentrations on the isotopic fractionation patterns of Phragmites australis (Cav.) Trin. ex Steud. Plants were grown for 40?d in a nutritive solution containing 3.2?μM (sufficient) or 2?mM (toxic) Zn. The Zn isotopic composition of roots, rhizomes, shoots, and leaves was analysed. Stems and leaves were sampled at different heights to evaluate the effect of long-distance transport on Zn fractionation. During Zn sufficiency, roots, rhizomes, and shoots were isotopically heavy (δ(66)Zn(JMC Lyon)=0.2‰) while the youngest leaves were isotopically light (-0.5‰). During Zn excess, roots were still isotopically heavier (δ(66)Zn=0.5‰) and the rest of the plant was isotopically light (up to -0.5‰). The enrichment of heavy isotopes at the roots was attributed to Zn uptake mediated by transporter proteins under Zn-sufficient conditions and to chelation and compartmentation in Zn excess. The isotopically lighter Zn in shoots and leaves is consistent with long-distance root to shoot transport. The tolerance response of P. australis increased the range of Zn fractionation within the plant and with respect to the environment.