Hybridization of invasive <Emphasis Type="Italic">Phragmites australis</Emphasis> with a native subspecies in North America

Interspecific hybridization can lead to the extinction of native populations and increased aggressiveness in hybrid forms relative to their parental lineages. However, interbreeding among subspecies is less often recognized as a serious threat to native species. Phragmites australis offers an excellent opportunity to investigate intraspecific hybridization since both native and introduced lineages occur in North America. Introduced Phragmites is a highly successful estuarine plant invader throughout North America, but native Phragmites populations are declining in the eastern US. Despite range overlaps, hybridization has not yet been detected between the native and introduced lineages in the wild, suggesting that phenological or physiological barriers preclude cross-pollination. We demonstrate, for the first time, that native and introduced populations of Phragmites can hybridize. There is substantial overlap in flowering period between native and introduced populations from the same geographic locations. We manually cross-pollinated native individuals with pollen from introduced Phragmites and recovered viable offspring. We then used microsatellite markers to prove that alleles unique to the pollen parent were transferred to progeny. Our results imply a mechanism for the further decline of native Phragmites in North America and a potential for the formation of aggressive hybrid offspring.     

Phylogenetic analyses of <Emphasis Type="Italic">Phragmites</Emphasis> spp. in southwest China identified two lineages and their hybrids

The species/lineage delimitation and possible hybridization/introgression are prerequisites in the management of invasive organism. Phragmites australis invaded diverse habitats and displaced the native lineages in North America as a consequence of the introduction from the Eurasia. Such species threatened the biodiversity safety of the invaded regions, in particular the biodiversity hot spots. Southwest (SW) China is a biodiversity hot spot with the occurrence of Phragmites species, both native and introduced. However, the genetic identity of Phragmites species in this biodiversity hot spot remains unclear, hampering effective ecological managements. In this study, we explored the phylogenetic lineages of Phragmites species in SW China. A total of 44 accessions sampled across SW China were analyzed using two chloroplast DNA (cpDNA) markers and amplified fragment length polymorphisms. Two genetic lineages were recovered, i.e., (1) the tropical lineage which primarily consisted of native Phragmites species represented by cpDNA haplotypes I, Q, and U in relatively low altitude and (2) the common lineage including native species at higher elevations in the Hengduan Mountains as well as artificially planted species represented by cpDNA haplotype P. The between-lineage hybridization was suggested for five analyzed accessions collected from either natural or artificial habitats. The putative hybrids might have originated from the maternal native tropical lineages and paternal introduced common lineage. Our results suggest the likelihood of introgressive hybridizations in SW China and thus provided implications for future research and ecological management.     

Preadaptation and post‐introduction evolution facilitate the invasion of Phragmites australis in North America

Compared with non‐invasive species, invasive plant species may benefit from certain advantageous traits, for example, higher photosynthesis capacity and resource/energy‐use efficiency. These traits can be preadapted prior to introduction, but can also be acquired through evolution following introduction to the new range. Disentangling the origins of these advantageous traits is a fundamental and emerging question in invasion ecology. We conducted a multiple comparative experiment under identical environmental condition with the invasive haplotype M lineage of the wetland grass Phragmites australis and compared the ecophysiological traits of this invasive haplotype M in North America with those of the European ancestor and the conspecific North American native haplotype E lineage, P. australis ssp. americanus. The invasive haplotype M differed significantly from the native North American conspecific haplotype E in several ecophysiological and morphological traits, and the European haplotype M had a more efficient photosynthetic apparatus than the native North American P. australis ssp. americanus. Within the haplotype M lineage, the introduced North American P. australis exhibited different biomass allocation patterns and resource/energy‐use strategies compared to its European ancestor group. A discriminant analysis of principal components separated the haplotype M and the haplotype E lineages completely along the first canonical axis, highly related to photosynthetic gas‐exchange parameters, photosynthetic energy‐use efficiency and payback time. The second canonical axis, highly related to photosynthetic nitrogen use efficiency and construction costs, significantly separated the introduced P. australis in North America from its European ancestor. Synthesis. We conclude that the European P. australis lineage was preadapted to be invasive prior to its introduction, and that the invasion in North America is further stimulated by rapid post‐introduction evolution in several advantageous traits. The multicomparison approach used in this study could be an effective approach for distinguishing preadaptation and post‐introduction evolution of invasive species. Further research is needed to link the observed changes in invasive traits to the genetic variation and the interaction with the environment.     

Invasion of Old World Phragmites australis in the New World: precipitation and temperature patterns combined with human influences redesign the invasive niche

After its introduction into North America, Euro‐Asian Phragmites australis became an aggressive invasive wetland grass along the Atlantic coast of North America. Its distribution range has since expanded to the middle, south and southwest of North America, where invasive P. australis has replaced millions of hectares of native plants in inland and tidal wetlands. Another P. australis invasion from the Mediterranean region is simultaneously occurring in the Gulf region of the United States and some countries in South America. Here, we analysed the occurrence records of the two Old World invasive lineages of P. australis (Haplotype M and Med) in both their native and introduced ranges using environmental niche models (ENMs) to assess (i) whether a niche shift accompanied the invasions in the New World; (ii) the role of biologically relevant climatic variables and human influence in the process of invasion; and (iii) the current potential distribution of these two lineages. We detected local niche shifts along the East Coast of North America and the Gulf Coast of the United States for Haplotype M and around the Mississippi Delta and Florida of the United States for Med. The new niche of the introduced Haplotype M accounts for temperature fluctuations and increased precipitation. The introduced Med lineage has enlarged its original subtropical niche to the tropics‐subtropics, invading regions with a high annual mean temperature (> ca. 10 °C) and high precipitation in the driest period. Human influence is an important factor for both niches. We suggest that an increase in precipitation in the 20th century, global warming and human‐made habitats have shaped the invasive niches of the two lineages in the New World. However, as the invasions are ongoing and human and natural disturbances occur concomitantly, the future distribution ranges of the two lineages may diverge from the potential distribution ranges detected in this study.     

What happens in Vegas,better stay in Vegas: <Emphasis Type="Italic">Phragmites australis</Emphasis> hybrids in the Las Vegas Wash

While hybridization between Native and Introduced Phragmites australis has not been documented across much of North America, it poses an ongoing threat to Native P. australis across its range. This is especially true for native populations in the biologically rich, but sparsely distributed wetlands of the southwest United States, which are among the most imperiled systems in North America. We identified multiple Hybrid P. australis stands in the Las Vegas Wash watershed, NV, a key regional link to the Colorado River basin. Rapid urbanization in this watershed has caused striking changes in water and nutrient inputs and the distribution of wetland habitats has also changed, with urban wetlands expanding but an overall reduction in wetland habitats regionally. Native P. australis has likely been present in the Wash wetland community in low abundance for thousands of years, but today Hybrid and Native plants dominate the shoreline along much of the Wash. In contrast, Introduced P. australis is rare, suggesting that opportunities for novel hybridization events remain uncommon. Hybrid crosses derived from both the native and introduced maternal lineages are widespread, although the conditions that precluded their establishment are unknown and we did not find evidence for backcrossing. Spread of Hybrid plants is likely associated with flooding events as well as restoration activities, including revegetation efforts and construction for erosion control, that have redistributed sediments containing P. australis rhizomes. Downstream escape of Hybrid plants to Lake Mead and wetlands throughout the lower Colorado River basin is of management concern as these Hybrids appear vigorous and could spread rapidly.     

Remnant native <Emphasis Type="Italic">Phragmites australis</Emphasis> maintains genetic diversity despite multiple threats

Over the past century, an increasing number of species have been negatively impacted by anthropogenic factors such as habitat disturbance and introduced species. One such plant, Phragmites australis subsp. americanus is a perennial emergent grass found in tidal and inland marshes of the Atlantic coast of the United States. While rarely dominant, it grows in mixed communities and across much of this area its distribution has been reduced dramatically, likely due to eutrophication and the invasion of conspecific P. australis introduced from Europe. In this study, two noncoding cpDNA markers and six microsatellite loci were used to characterize genetic diversity among 58 remnant native P. australis stands from North Carolina to Maine. Five chloroplast DNA haplotypes were identified along with 42 multilocus genotypes. Bayesian exploration detected no population structure (e.g., optimal K = 1), indicating that these individuals form a single population. The analysis also detected no presence of hybrids of native and introduced P. australis in the samples, despite the close proximity of individuals to each other in many cases. These results suggest that the genetic composition of native P. australis across the region remains homogeneous and pure, providing managers with justification for its conservation and a potentially large source of germplasm for use in restoration activities.     

Evidence for multiple introductions of Phragmites australis to North America: detection of a new non-native haplotype

We found a new non-native haplotype of Phragmites australis in North America that provides convincing evidence for multiple introductions of this highly invasive reed from Europe. Prior to our detection of this new non-native haplotype, invasion of North America by this reed grass was thought to be limited to a single cp-DNA haplotype–haplotype M. However, we found two sites colonized by haplotype L1 in Quebec, Canada, a haplotype native to northern Europe, Great Britain and Romania. Because the invasion of North America by P. australis is ongoing, and because there is evidence for intra- and inter-specific hybridization and increased fecundity resulting from outcrossing, more attention should be paid to genetic differences and associated vigor of populations of introduced Phragmites across North America.     

Biogeography of <Emphasis Type="Italic">Phragmites</Emphasis><Emphasis Type="Italic">australis</Emphasis> lineages in the southwestern United States

The environmental and social impacts of Phragmites australis invasion have been extensively studied in the eastern United States. In the West where the invasion is relatively recent, a lack of information on distributions and spread has limited our ability to manage invasive populations or assess whether native populations will experience a decline similar to that in the East. Between 2006 and 2015, we evaluated the genetic status, distribution, and soil properties (pH, electrical conductivity, and soil texture) of Phragmites stands in wetlands and riparian systems throughout the Southwest. Native (subspecies americanus), Introduced (haplotype M), and Gulf Coast (subspecies berlandieri) Phragmites lineages were identified in the survey region, as well as watershed-scale hybridization between the Native and Introduced lineages in southern Nevada. Two Asian haplotypes (P and Q) that were previously not known to occur in North America were found in California. The Native lineage was the most frequent and widespread across the region, with four cpDNA haplotypes (A, B, H, and AR) occurring at low densities in all wetland types. Most Introduced Phragmites stands were in or near major urban centers and associated with anthropogenic disturbance in wetlands and rivers, and we document their spread in the region, which is likely facilitated by transportation and urban development. Soil pH of Native and hybrid stands was higher (averaging 8.3 and 8.6, respectively) than Introduced stands (pH of 7.5) and was the only soil property that differed among lineages. Continued monitoring of all Phragmites lineages in the Southwest will aid in assessing the conservation status of Native populations and developing management priorities for non-native stands.     

Invasion of <Emphasis Type="Italic">Nipponaclerda biwakoensis</Emphasis> (Hemiptera: Aclerdidae) and <Emphasis Type="Italic">Phragmites australis</Emphasis> die-back in southern Louisiana,USA

Common reed, Phragmites australis (Cav.) Trin. Ex Steud., is the dominant emergent vegetation in the lower Mississippi River Delta (MRD), Louisiana, USA and is comprised primarily of introduced lineages of different phylogeographic origins. Dense stands of P. australis are important for protecting marsh soils from wave action and storm surges. In the Fall of 2016, while investigating symptoms of die-back of Phragmites stands in the lower marsh, a non-native scale was found infesting affected stands in high densities. Identified as Nipponaclerda biwakoensis (Kuwana) (Hemiptera: Aclerdidae), the scale was well established across the lower MRD. This report represents the first recorded population of Nipponaclerda biwakoensis in North America. Intriguingly, there are noticeable differences in die-back symptoms and in scale densities among different lineages of Phragmites in the MRD, with stands of the well-known European invasive lineage appearing healthier and having lower scale densities than other Phragmites lineages. Given its apparent relationship with the die-back syndrome, the scale may have serious implications for the health and stability of Phragmites marsh communities across coastal Louisiana. Efforts are currently underway to investigate the role of the scale and other abiotic stressors in the die-backs and potential management solutions.     

Genetic and epigenetic changes during the invasion of a cosmopolitan species (Phragmites australis)

While many introduced invasive species can increase genetic diversity through multiple introductions and/or hybridization to colonize successfully in new environments, others with low genetic diversity have to persist by alternative mechanisms such as epigenetic variation. Given that Phragmites australis is a cosmopolitan reed growing in a wide range of habitats and its invasion history, especially in North America, has been relatively well studied, it provides an ideal system for studying the role and relationship of genetic and epigenetic variation in biological invasions. We used amplified fragment length polymorphism (AFLP) and methylation‐sensitive (MS) AFLP methods to evaluate genetic and epigenetic diversity and structure in groups of the common reed across its range in the world. Evidence from analysis of molecular variance (AMOVA) based on AFLP and MS‐AFLP data supported the previous conclusion that the invasive introduced populations of P. australis in North America were from European and Mediterranean regions. In the Gulf Coast region, the introduced group harbored a high level of genetic variation relative to originating group from its native location, and it showed epigenetic diversity equal to that of the native group, if not higher, while the introduced group held lower genetic diversity than the native. In the Great Lakes region, the native group displayed very low genetic and epigenetic variation, and the introduced one showed slightly lower genetic and epigenetic diversity than the original one. Unexpectedly, AMOVA and principal component analysis did not demonstrate any epigenetic convergence between native and introduced groups before genetic convergence. Our results suggested that intertwined changes in genetic and epigenetic variation were involved in the invasion success in North America. Although our study did not provide strong evidence proving the importance of epigenetic variation prior to genetic, it implied the similar role of stable epigenetic diversity to genetic diversity in the adaptation of P. australis to local environment.     

Impact of Archanara geminipuncta (Lepidoptera: Noctuidae) on aboveground biomass production of Phragmites australis

Management of invasive plants with biological control rests on the assumption of herbivores as structuring forces of plant community composition, but only 30% of programs achieve substantial plant suppression. Control is often caused by a few successful agents, and improvements in the ability to select the most promising species would greatly improve weed biocontrol programs. We evaluated impact of different larval stages and larval densities of the stem boring noctuid Archanara geminipuncta on height and biomass production of Phragmites australis in the field and in a common garden in the native European range. In the field, stem biomass was reduced 21.5–64.5% by A. geminipuncta attack with the largest reduction due to early larval feeding. In the common garden, P. australis performance declined linearly (stem height 40%, biomass 50%; and percentage of flowering stems 90%) as attack rates increased. Significant field and common garden impact and the large Eurasian distribution indicate great potential of A. geminipuncta for biocontrol of introduced P. australis in North America if host specificity tests produce favorable results. If approved for release, we anticipate that A. geminipuncta could establish throughout the range of introduced P. australis in North America. We also anticipate that this moth will build high populations with significant impact on height, aboveground biomass, and clonal expansion of P. australis. This attack is expected to reduce competitive ability of P. australis, favoring native wetland species and preventing further negative ecological impacts associated with the current spread of introduced P. australis in North America.     

Phragmites australis root secreted phytotoxin undergoes photo-degradation to execute severe phytotoxicity

Our study organism, Phragmites australis (common reed), is a unique invader in that both native and introduced lineages are found coexisting in North America. This allows one to make direct assessments of physiological differences between these different subspecies and examine how this relates to invasiveness. Recent efforts to understand plant invasive behavior show that some invasive plants secrete a phytotoxin to ward-off encroachment by neighboring plants (allelopathy) and thus provide the invaders with a competitive edge in a given habitat. Here we show that a varying climatic factor like ultraviolet (UV) light leads to photo-degradation of secreted phytotoxin (gallic acid) in P. australis rhizosphere inducing higher mortality of susceptible seedlings. The photo-degraded product of gallic acid (hereafter GA), identified as mesoxalic acid (hereafter MOA), triggered a similar cell death cascade in susceptible seedlings as observed previously with GA. Further, we detected the biological concentrations of MOA in the natural stands of exotic and native P. australis. Our studies also show that the UV degradation of GA is facilitated at an alkaline pH, suggesting that the natural habitat of P. australis may facilitate the photo-degradation of GA. The study highlights the persistence of the photo-degraded phytotoxin in the P. australis''s rhizosphere and its inhibitory effects against the native plants.Key words: ultraviolet, gallic acid, mesoxalic acid, novel weapons, invasive species, Phragmites australis     

Soil conditioning effects of Phragmites australis on native wetland plant seedling survival

Interactions between introduced plants and soils they colonize are central to invasive species success in many systems. Belowground biotic and abiotic changes can influence the success of introduced species as well as their native competitors. All plants alter soil properties after colonization but, in the case of many invasive plant species, it is unclear whether the strength and direction of these soil conditioning effects are due to plant traits, plant origin, or local population characteristics and site conditions in the invaded range. Phragmites australis in North America exists as a mix of populations of different evolutionary origin. Populations of endemic native Phragmites australis americanus are declining, while introduced European populations are important wetland invaders. We assessed soil conditioning effects of native and non‐native P. australis populations on early and late seedling survival of native and introduced wetland plants. We further used a soil biocide treatment to assess the role of soil fungi on seedling survival. Survival of seedlings in soils colonized by P. australis was either unaffected or negatively affected; no species showed improved survival in P. australis‐conditioned soils. Population of P. australis was a significant factor explaining the response of seedlings, but origin (native or non‐native) was not a significant factor. Synthesis: Our results highlight the importance of phylogenetic control when assessing impacts of invasive species to avoid conflating general plant traits with mechanisms of invasive success. Both native (noninvasive) and non‐native (invasive) P. australis populations reduced seedling survival of competing plant species. Because soil legacy effects of native and non‐native P. australis are similar, this study suggests that the close phylogenetic relationship between the two populations, and not the invasive status of introduced P. australis, is more relevant to their soil‐mediated impact on other plant species.     

The effect of nutrients on seedling growth of native and introduced Phragmites australis

Differing responses to abiotic stresses and increased nutrient availability may play a role in the invasion and spread of introduced Phragmites australis Cav. (Trin.) ex. Steud. and the decline of native P.a. americanus Saltonstall, P.M. Peterson & Soreng in North America. We present results from an outdoor experiment where native and introduced P. australis seedlings were grown under two nutrient treatments. Both subspecies responded positively to increased nutrients but introduced plants clearly outperformed natives, growing taller, producing more stems, and had three to four times higher biomass. The biomass of introduced P. australis growing in low nutrients was similar to that of the native in high nutrients. Aboveground:belowground biomass ratios were nearly 1.25 for both native and introduced plants across treatments and reflect the high investment P. australis seedlings place on shoot production in their first year of growth. Our results also demonstrate that introduced P. australis can have explosive growth over a single growing season, even when established from seed. This implies that management of young, newly established populations may be prudent where introduced P. australis is considered undesirable, irregardless of whether eutrophication is an issue.     

No apparent effects of soil inoculum on green frog (Lithobates clamitans Latreille) tadpole performance

Invasions by nonnative plant species are transforming plant communities across the globe. An important challenge for ecologists is to understand how animals will respond to these changes. One way that plant invasions could affect aquatic animals is by changing the rate at which soil communities decompose litter, which could alter the flow of energy and nutrients from plant litter to aquatic communities. In this study, we measured larval amphibian responses to soil conditioned by either introduced or native genotypes of Phragmites australis L. (common reed) in northeastern North America. We collected soil from adjacent stands of introduced and native P. australis at three sites in central New York and inoculated outdoor aquatic mesocosms with soil extracts. Mesocosms contained six Lithobates clamitans Latreille (green frog) tadpoles and either low- or high-quality native P. australis americanus litter. We found that litter decomposition differed based on soil inoculum, and we observed a significant interaction between litter quality and soil inoculum; higher-quality litter tended to decompose faster when exposed to inocula from introduced P. australis, while lower-quality litter tended to decompose faster when exposed to inocula from native P. australis americanus. Tadpoles raised with high-quality litter developed faster and achieved greater body size, but soil inocula had no apparent effect on tadpoles. Our results suggest that plant invasions may alter microbial communities, causing subtle changes in litter decomposition rates, but these changes do not appear strong enough to influence larvae of a widespread amphibian.     

Living in two worlds: Evolutionary mechanisms act differently in the native and introduced ranges of an invasive plant

Identifying the factors that influence spatial genetic structure among populations can provide insights into the evolution of invasive plants. In this study, we used the common reed (Phragmites australis), a grass native in Europe and invading North America, to examine the relative importance of geographic, environmental (represented by climate here), and human effects on population genetic structure and its changes during invasion. We collected samples of P. australis from both the invaded North American and native European ranges and used molecular markers to investigate the population genetic structure within and between ranges. We used path analysis to identify the contributions of each of the three factors—geographic, environmental, and human‐related—to the formation of spatial genetic patterns. Genetic differentiation was observed between the introduced and native populations, and their genetic structure in the native and introduced ranges was different. There were strong effects of geography and environment on the genetic structure of populations in the native range, but the human‐related factors manifested through colonization of anthropogenic habitats in the introduced range counteracted the effects of environment. The between‐range genetic differences among populations were mainly explained by the heterogeneous environment between the ranges, with the coefficient 2.6 times higher for the environment than that explained by the geographic distance. Human activities were the primary contributor to the genetic structure of the introduced populations. The significant environmental divergence between ranges and the strong contribution of human activities to the genetic structure in the introduced range suggest that invasive populations of P. australis have evolved to adapt to a different climate and to human‐made habitats in North America.     

Microsatellite variation within and among North American lineages of Phragmites australis

Over the past century, the spread of the common reed (Phragmites australis) has had a dramatic impact on wetland communities across North America. Although native populations of Phragmites persist, introduced invasive populations have dominated many sites and it is not clear if the two types can interbreed. This study compares patterns of differentiation in 10 microsatellite loci among North American and European Phragmites individuals with results obtained from sequencing of noncoding chloroplast DNA. Three population lineages (native, introduced and Gulf Coast) were previously identified in North America from chloroplast DNA and similar structuring was found in the nuclear genome. Each lineage was distinguished by unique alleles and allele combinations and the introduced lineage was closely related to its hypothesized source population in Europe. Size homoplasy and diagnostic base substitutions distinguishing lineages were evident at several loci, further emphasizing that native, introduced and Gulf Coast North American Phragmites lineages are genetically distinct. Gene flow between lineages was low and invasive introduced populations do not represent a hybrid population type.     

Distribution and impact of exotic gall flies (Lipara sp.) on native and exotic Phragmites australis

Two exotic gall fly species infest stems of native and exotic Phragmites australis (Cav.) Trin. ex Steudel in northeastern North America. In this study, we determined the distribution of Lipara similis Schiner and L. rufitarsis Loew in native and exotic P. australis in Rhode Island. We also studied the within-stand distributions of each fly species and their effects on flowering of native and exotic P. australis. We collected stems from populations throughout southern Rhode Island and measured stem length and diameter, and percent flowering. Stems were then dissected to determine Lipara infestation. L. similis and L. rufitarsis were found throughout Rhode Island infesting both native and exotic P. australis, but their presence and abundance varied among sites. Within stands, L. similis infests the taller, thicker interior stems and L. rufitarsis infests the shorter, thinner exterior stems. Lipara similis reduces stem length by 6%; L. rufitarsis infestation reduces stem length by 37%. The flowering rate of uninfested stems is significantly lower in native P. australis stems than in exotic stems. Both Lipara species prevent infested stems from flowering. In adjacent stands of native and exotic P. australis, L. rufitarsis infests significantly more native stems than exotic stems, possibly further reducing the reproductive potential of the native plants relative to the exotic. Lipara species may play a role in facilitating the displacement of native P. australis by the exotic genotype.     

Jack-and-Master Trait Responses to Elevated CO2 and N: A Comparison of Native and Introduced Phragmites australis

Global change is predicted to promote plant invasions world-wide, reducing biodiversity and ecosystem function. Phenotypic plasticity may influence the ability of introduced plant species to invade and dominate extant communities. However, interpreting differences in plasticity can be confounded by phylogenetic differences in morphology and physiology. Here we present a novel case investigating the role of fitness trait values and phenotypic plasticity to global change factors between conspecific lineages of Phragmites australis. We hypothesized that due to observed differences in the competitive success of North American-native and Eurasian-introduced P. australis genotypes, Eurasian-introduced P. australis would exhibit greater fitness in response to global change factors. Plasticity and plant performance to ambient and predicted levels of carbon dioxide and nitrogen pollution were investigated to understand how invasion pressure may change in North America under a realistic global change scenario. We found that the introduced Eurasian genotype expressed greater mean trait values in nearly every ecophysiological trait measured – aboveground and belowground – to elevated CO₂ and nitrogen, outperforming the native North American conspecific by a factor of two to three under every global change scenario. This response is consistent with “jack and master” phenotypic plasticity. We suggest that differences in plant nitrogen productivity, specific leaf area, belowground biomass allocation, and inherently higher relative growth rate are the plant traits that may enhance invasion of Eurasian Phragmites in North America. Given the high degree of genotypic variability within this species, and our limited number of genotypes, our results must be interpreted cautiously. Our study is the first to demonstrate the potential importance of jack-and-master phenotypic plasticity in plant invasions when facing imminent global change conditions. We suggest that jack-and-master invasive genotypes and/or species similar to introduced P. australis will have an increased ecological fitness, facilitating their invasion in both stressful and resource rich environments.     

Biology of Platycephala planifrons (Diptera: Chloropidae) and its potential effectiveness as biological control agent for invasive Phragmites australis in North America

Phragmites australis is a cosmopolitan clonal grass valued for its support of diversity-rich communities in its native range and feared for its devastating effects on native diversity where the species is introduced. Lack of successful control in North America resulted in the initiation of a biological control program. We used a combination of field surveys and common garden experiments in Europe to study life history and ecology of a chloropid fly, Platycephala planifrons, to assess its potential as a biological control agent. The fly is widely distributed (in non-flooded sites) throughout Eurasia but attack rates are generally low (mean 5–10%; max. 29%). Adults emerge in late June and may live for several months. Females lay eggs at the base of Ph. australis shoots. First instar larvae of this stem-feeding fly overwinter in dormant below-ground shoots of Ph. australis and rapidly complete development in early spring. Larval feeding destroys the growing meristem of the shoot causing premature wilting and 60–70% reductions in shoot biomass production. Early season attack and considerable impact suggest that Pl. planifrons could be a potent biocontrol agent, if it can escape suppression by natural enemies in the introduced range. However, the generally low attack rates in its native range and its dependence on dry sites appear to make the species a “second-choice” candidate for potential release in North America.