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It is increasingly recognized that different genetic variants of hosts can uniquely shape their microbiomes. Invasive species often evolve in their introduced ranges, but little is known about the potential for their microbial associations to change during invasion as a result. We asked whether host genotype (G), microbial environment (E), or their interaction (G × E) affected the composition and diversity of host-associated microbiomes in Centaurea solstitialis (yellow starthistle), a Eurasian plant that is known to have evolved novel genotypes and phenotypes and to have altered microbial interactions, in its severe invasion of CA, USA. We conducted an experiment in which native and invading plant genotypes were inoculated with native and invaded range soil microbial communities. We used amplicon sequencing to characterize rhizosphere bacteria in both the experiment and the field soils from which they were derived. We found that native and invading plant genotypes accumulated different microbial associations at the family level in each soil community, often counter to differences in family abundance between soil communities. Root associations with potentially beneficial Streptomycetaceae were particularly interesting, as these were more abundant in the invaded range field soil and accumulated on invading genotypes. We also found that bacterial diversity is higher in invaded soils, but that invading genotypes accumulated a lower diversity of bacteria and unique microbial composition in experimental inoculations, relative to native genotypes. Thus variation in microbial associations of invaders was driven by the interaction of plant G and microbial E, and rhizosphere microbial communities appear to change in composition in response to host evolution during invasion. [ABSTRACT FROM AUTHOR]

Plants demonstrate exceptional variation in genome size across species, and their genome sizes can also vary dramatically across individuals and populations within species. This aspect of genetic variation can have consequences for traits and fitness, but few studies attributed genome size differentiation to ecological and evolutionary processes. Biological invasions present particularly useful natural laboratories to infer selective agents that might drive genome size shifts across environments and population histories. Here, we test hypotheses for the evolutionary causes of genome size variation across 14 invading populations of yellow starthistle, Centaurea solstitialis, in California, United States. We use a survey of genome sizes and trait variation to ask: (1) Is variation in genome size associated with developmental trait variation? (2) Are genome sizes smaller toward the leading edge of the expansion, consistent with selection for "colonizer" traits? Or alternatively, does genome size increase toward the leading edge of the expansion, consistent with predicted consequences of founder effects and drift? (3) Finally, are genome sizes smaller at higher elevations, consistent with selection for shorter development times? We found that 2C DNA content varied 1.21‐fold among all samples, and was associated with flowering time variation, such that plants with larger genomes reproduced later, with lower lifetime capitula production. Genome sizes increased toward the leading edge of the invasion, but tended to decrease at higher elevations, consistent with genetic drift during range expansion but potentially strong selection for smaller genomes and faster development time at higher elevations. These results demonstrate how genome size variation can contribute to traits directly tied to reproductive success, and how selection and drift can shape that variation. We highlight the influence of genome size on dynamics underlying a rapid range expansion in a highly problematic invasive plant. [ABSTRACT FROM AUTHOR]

Classical biological control is an important method for controlling invasive alien weeds. Univoltine insects can be highly effective biological control agents of annual weeds because they are well synchronized with their host plant. However, having only one generation per year makes it difficult and slow to multiply them in the laboratory for initial field releases. If it were possible to terminate reproductive diapause early, then we could rear multiple generations per year, which would greatly increase annual production. We used a recently approved biocontrol agent, Ceratapion basicorne (a univoltine weevil), for yellow starthistle (Centaurea solstitialis) as a model system to study the use of two insect hormones, 20-hydroxyecdysone (20E) and methoprene, to terminate reproductive diapause. Methoprene (1 μg applied topically) terminated reproductive diapause of female weevils, whereas doses of 0.0, 0.01 and 0.1 μg did not. The combination of methoprene and 20E had a stronger effect and induced an increase in eggs (1.51 ± 0.16 eggs/day, mean ± SE) compared with a methoprene only group (1.00 ± 0.13 eggs/day), and a control group (0.21 ± 0.04 eggs/day). Thus, topical application of these hormones should enable us to rear the weevil out of its normal season and produce more than one generation per year, which will increase productivity of mass-rearing it for field release. Once released in the field, the insect would continue as a univoltine agent that is well-synchronized with its host plant.

Abstract Plants demonstrate exceptional variation in genome size across species, and their genome sizes can also vary dramatically across individuals and populations within species. This aspect of genetic variation can have consequences for traits and fitness, but few studies attributed genome size differentiation to ecological and evolutionary processes. Biological invasions present particularly useful natural laboratories to infer selective agents that might drive genome size shifts across environments and population histories. Here, we test hypotheses for the evolutionary causes of genome size variation across 14 invading populations of yellow starthistle, Centaurea solstitialis, in California, United States. We use a survey of genome sizes and trait variation to ask: (1) Is variation in genome size associated with developmental trait variation? (2) Are genome sizes smaller toward the leading edge of the expansion, consistent with selection for “colonizer” traits? Or alternatively, does genome size increase toward the leading edge of the expansion, consistent with predicted consequences of founder effects and drift? (3) Finally, are genome sizes smaller at higher elevations, consistent with selection for shorter development times? We found that 2C DNA content varied 1.21‐fold among all samples, and was associated with flowering time variation, such that plants with larger genomes reproduced later, with lower lifetime capitula production. Genome sizes increased toward the leading edge of the invasion, but tended to decrease at higher elevations, consistent with genetic drift during range expansion but potentially strong selection for smaller genomes and faster development time at higher elevations. These results demonstrate how genome size variation can contribute to traits directly tied to reproductive success, and how selection and drift can shape that variation. We highlight the influence of genome size on dynamics underlying a rapid range expansion in a highly problematic invasive plant.

Invasive species often possess a great capacity to adapt to novel environments in the form of spatial trait variation, as a result of varying selection regimes, genetic drift, or plasticity. We explored the geographic differentiation in several phenotypic traits related to plant growth, reproduction, and defense in the highly invasive Centaurea solstitialis by measuring neutral genetic differentiation (FST), and comparing it with phenotypic differentiation (PST), in a common garden experiment in individuals originating from regions representing the species distribution across five continents. Native plants were more fecund than non‐native plants, but the latter displayed considerably larger seed mass. We found indication of divergent selection for these two reproductive traits but little overall genetic differentiation between native and non‐native ranges. The native versus invasive PST–FST comparisons demonstrated that, in several invasive regions, seed mass had increased proportionally more than the genetic differentiation. Traits displayed different associations with climate variables in different regions. Both capitula numbers and seed mass were associated with winter temperature and precipitation and summer aridity in some regions. Overall, our study suggests that rapid evolution has accompanied invasive success of C. solstitialis and provides new insights into traits and their genetic bases that can contribute to fitness advantages in non‐native populations. [ABSTRACT FROM AUTHOR]

Many endosymbionts of insects have been shown to manipulate and alter their hosts' reproduction with implications for agriculture, disease transmission, and ecological systems. Less studied are the microbiota of classical biological control agents and the implications of inadvertent endosymbionts in laboratory colonies for field establishment and effects on target pests or nontarget organisms. While native-range field populations of agents may have a low incidence of vertically transmitted endosymbionts, quarantine and laboratory rearing of inbred populations may increase this low prevalence to fixation in relatively few generations. Fixation of detrimental endosymbionts in founding biological control agent populations prior to release may have far-reaching effects. Significant female-biased sex-ratio distortion was found within laboratory populations of the weevil Ceratapion basicorne (Illiger), a classical biological control agent that was recently approved for use against yellow starthistle (Centaurea solstitialis L.). This sex-ratio distortion was observed to be vertically inherited and reversible through antibiotic treatment of the host insect. Molecular diagnostics identified a Rickettsia sp. as the only bacterial endosymbiont present in breeding lines with distorted sex ratios and implicated this as the first reported Rickettsia associated with sex-ratio distortion within the superfamily Curculionoidea., (© The Author(s) 2024. Published by Oxford University Press on behalf of Entomological Society of America.)

Invasive species have the ability to rapidly adapt in the new regions where they are introduced. Classic evolutionary theory predicts that the accumulation of genetic differences over time in allopatric isolation may lead to reproductive incompatibilities resulting in decreases in reproductive success and, eventually, to speciation. However, experimental evidence for this theoretical prediction in the context of invasive species is lacking. We aimed to test for the potential of allopatry to determine reproductive success of invasive plants, by experimentally admixing genotypes from six different native and non‐native regions of Centaurea solstitialis, an invasive forb for which preliminary studies have detected some degree of reproductive isolation between one native and non‐native region.We grew plants under common garden conditions and outcrossed individuals originating from different source populations in the native and introduced range to evaluate reproductive success in terms of seed to ovule ratio produced. We also assessed geographical and genetic isolation among C. solstitialis regions as a potential driving factor of reproductive success.Experimental admixture generated mixed fitness effects, including significant increases, decreases and no differences in reproductive success as compared to crosses within population (control). Centaurea solstitialis invasive populations in the Americas generated preponderantly negative fitness interactions, regardless of the pollen source, suggesting selection against immigrants and reinforcement. Other non‐native populations (Australia) as well as individuals from the native range of Spain demonstrated an increase in fitness for between‐region crosses, indicating inbreeding. These differences show an asymmetrical response to inter‐regional gene flow, but no evidence of isolation by distance.Synthesis. The speed of adaptation and the accumulation of reproductive incompatibilities among allopatric populations of invasive species might be more rapid than previously assumed. Our data show a global mosaic of reproductive outputs, showcasing an array of evolutionary processes unfolding during colonization at large biogeographical scales. [ABSTRACT FROM AUTHOR]

At two field sites that differed in fertility, we investigated how species richness, functional group diversity, and species composition of constructed plant communities influenced invasion. Grassland communities were constructed to be either functionally diverse or functionally simple based on belowground resource use patterns of constituent species. Communities were also constructed with different numbers of species (two or five) to examine interactions between species richness, functional diversity and invasion resistance. We hypothesized that communities with more complementary belowground resource use (i.e., more species rich and more functionally diverse communities) would be less easily invaded than communities with greater degrees of belowground resource use overlap. Two contrasting invasive species were introduced: an early-season, shallow rooting annual grass, Bromus hordeaceus (soft chess), and a late-season, deep rooting annual forb, Centaurea solstitialis (yellow starthistle). Invader responses to species richness and functional diversity treatments differed between sites. In general, the more similar the patterns of belowground resource use between residents of the plant community and the invader, the poorer the invader’s performance. Complementarity or overlap of resource use among species in the constructed communities appeared to affect invader success less than complementarity or overlap of resource use between the invader and the species present in the community.

Resistance to conventional antimicrobial regimes is one of the issues of concern in healthcare and it drives the need for development of new antimicrobial agents. Medicinal plants, as rich source of biochemical and bioactive compounds, serve as potential source for new drugs. Here, we evaluated the ethanolic extract of Centaurea solstitialis L. and its different fractions (n-hexane, choloroform and n-butanol soluble fraction) for antimicrobial, antioxidant and enzymes inhibitory activities. Antibacterial activity against two Gram-positive and three Gram-negative bacteria species were determined by using agar well diffusion and 96-wells microplate methods. Similarly, antifungal activity against two fungal strains was also evaluated by agar well diffusion method. Antioxidant activity analyzed by measuring the scavenging activity of DPPH radicals and acetylcholinesterase, butrylcholinesterase and chymotrypsin inhibitory activity was determined at 10 µg/mL and 1.0 mg/mL concentrations. Results revealed that the ethanolic extract of C. solstitialis and its different fractions possesses significant (P<0.05) antibacterial activity and effective against fungi Aspergillus niger and Macrophomina phaseolina. Significant (P<0.05) DPPH scavenging activity (88.52±0.23%) among all fractions was noted. n-Butanol fraction showed significant acetylcholinesterase (78.55±0.76%) and butrylcholinesterase inhibitory activity (78.1±0.41%) with IC50 values of 54.6±0.39 µg/mL and 211.9±0.15 µg/mL, respectively. Maximum chymotrypsin inhibition activity was shown by crude ethanolic extract (87.76±1.17) with IC50 value of 38.23±0.75 µg/mL. It is concluded that C. solstitialis extract and its fractions possess significant antimicrobial, antioxidant and enzyme inhibitory activity. [ABSTRACT FROM AUTHOR]

Invasive plants are associated with the decline of native plant richness, but the impact of removal of invasives on native plant richness is often unknown. We investigated whether the presence of the introduced plant Centaurea solstitialis (Asteraceae) was correlated with reduced native plant richness; whether rain in late spring, when C.solstitialis is virtually the only plant actively growing, increased its cover; and whether native species richness increased following the control of C.solstitialis. From 2011 to 2017 in a grassland in Sonoma County, California, USA, we treated 20 1-m2 plots in C.solstitialis-invaded patches with chemical and mechanical removal. We monitored cover of all plants in those plots, plus 20 invaded untreated and 20 uninvaded plots, for a total of 60 plots in two blocks. Native plant richness was lower in invaded than in non-invaded plots. More late spring rainfall resulted in greater C.solstitialis cover in the following year. Native species richness in the six years after initial removal was slightly higher in removal plots than in untreated control plots. Centaurea solstitialis removal alone results in modest benefits for native plant species richness. Managing this invasive requires more resources in years with more late spring rainfall. [ABSTRACT FROM AUTHOR]

Yellow starthistle is an exotic invasive weed that is estimated to infest over 14 million acres in California and is considered the most common exotic weed statewide. We reviewed several previous studies and conducted a township survey to provide an up-to-date analysis of the weed’s rapid spread throughout the state. A county-by-county comparison between 1985 and 2002 showed increases in yellow starthistle in all regions of the state except for northeast California and the southeast desert region. Currently, most infestations occur in Northern California, but future invasions and spread will likely occur in the coastal counties of Southern California.

The herbicide clopyralid (Transline) is commonly applied by air to control yellow starthistle, a noxious weed, in California. In laboratory studies, clopyralid toxicity in Fowler’s toad was low, indicating a wide safety margin when used under field conditions. In addition, monitoring of clopyralid drift following aerial application demonstrated that 98-foot (30-meter) buffers between treatment areas and water sources provided adequate drift protection for an adjacent stream and vernal pools. Nevertheless, to ensure that movement of the herbicide to water sources is minimized, it is important to prevent application error, particularly accidental encroachment into established buffer zones. This study demonstrated that drift potential for clopyralid was minimal even with an aerial application and a slight downwind breeze toward sensitive aquatic sites. It is also the first report demonstrating a high tolerance to clopyralid in larval toads.

Classical biological control is an important method for controlling invasive alien weeds. Univoltine insects can be highly effective biological control agents of annual weeds because they are well synchronized with their host plant. However, having only one generation per year makes it difficult and slow to multiply them in the laboratory for initial field releases. If it were possible to terminate reproductive diapause early, then we could rear multiple generations per year, which would greatly increase annual production. We used a recently approved biocontrol agent, Ceratapion basicorne (a univoltine weevil), for yellow starthistle (Centaurea solstitialis) as a model system to study the use of two insect hormones, 20-hydroxyecdysone (20E) and methoprene, to terminate reproductive diapause. Methoprene (1 μg applied topically) terminated reproductive diapause of female weevils, whereas doses of 0.0, 0.01 and 0.1 μg did not. The combination of methoprene and 20E had a stronger effect and induced an increase in eggs (1.51 ± 0.16 eggs/day, mean ± SE) compared with a methoprene only group (1.00 ± 0.13 eggs/day), and a control group (0.21 ± 0.04 eggs/day). Thus, topical application of these hormones should enable us to rear the weevil out of its normal season and produce more than one generation per year, which will increase productivity of mass-rearing it for field release. Once released in the field, the insect would continue as a univoltine agent that is well-synchronized with its host plant.

The impact of the capitulum weevil Eustenopus villosus on Centaurea solstitialis seed production was examined at two field sites in central California. The study occurred in 1993–1995 during the early phases of the biological control program on C. solstitialis and before the current guild of capitulum insects had become widespread. Results showed that adult feeding on early flower buds resulted in 60–70% of buds failing to develop. Regrowth delayed capitulum production by 9 days and extended production by 4 weeks at season end. Between 69% and 92% of capitula were punctured from feeding or oviposition but the occurrence of larvae in capitula ranged from 27% to 49%. Seed production in C. solstitialis capitula increased linearly with size. The occurrence of larvae was proportionally higher in larger capitula (>8 mm) but the probability of attack for individual capitula did not vary with plant size. Total seed loss from larval feeding ranged from 34 to 47%. It is recommended that another survey be performed to determine if the level of infestation of E. villosus has increased since its initial introduction.

The margins of an expanding range are predicted to be challenging environments for adaptation. Marginal populations should often experience low effective population sizes (Ne) where genetic drift is high due to demographic expansion and/or census population size is low due to unfavourable environmental conditions. Nevertheless, invasive species demonstrate increasing evidence of rapid evolution and potential adaptation to novel environments encountered during colonization, calling into question whether significant reductions in Ne are realized during range expansions in nature. Here we report one of the first empirical tests of the joint effects of expansion dynamics and environment on effective population size variation during invasive range expansion. We estimate contemporary values of Ne using rates of linkage disequilibrium among genome‐wide markers within introduced populations of the highly invasive plant Centaurea solstitialis (yellow starthistle) in North America (California, USA), and within native Eurasian populations. As predicted, we find that Ne within the invaded range is positively correlated with both expansion history (time since founding) and habitat quality (abiotic climate). History and climate had independent additive effects with similar effect sizes, indicating an important role for both factors in this invasion. These results support theoretical expectations for the population genetics of range expansion, though whether these processes can ultimately arrest the spread of an invasive species remains an unanswered question. [ABSTRACT FROM AUTHOR]

Plants demonstrate exceptional variation in genome size across species, and their genome sizes can also vary dramatically across individuals and populations within species. This aspect of genetic variation can have consequences for traits and fitness, but few studies attributed genome size differentiation to ecological and evolutionary processes. Biological invasions present particularly useful natural laboratories to infer selective agents that might drive genome size shifts across environments and population histories. Here, we test hypotheses for the evolutionary causes of genome size variation across 14 invading populations of yellow starthistle, Centaurea solstitialis , in California, United States. We use a survey of genome sizes and trait variation to ask: (1) Is variation in genome size associated with developmental trait variation? (2) Are genome sizes smaller toward the leading edge of the expansion, consistent with selection for "colonizer" traits? Or alternatively, does genome size increase toward the leading edge of the expansion, consistent with predicted consequences of founder effects and drift? (3) Finally, are genome sizes smaller at higher elevations, consistent with selection for shorter development times? We found that 2C DNA content varied 1.21-fold among all samples, and was associated with flowering time variation, such that plants with larger genomes reproduced later, with lower lifetime capitula production. Genome sizes increased toward the leading edge of the invasion, but tended to decrease at higher elevations, consistent with genetic drift during range expansion but potentially strong selection for smaller genomes and faster development time at higher elevations. These results demonstrate how genome size variation can contribute to traits directly tied to reproductive success, and how selection and drift can shape that variation. We highlight the influence of genome size on dynamics underlying a rapid range expansion in a highly problematic invasive plant., Competing Interests: The authors declare no conflict of interest., (© 2023 The Authors. Evolutionary Applications published by John Wiley & Sons Ltd.)

Species introductions often bring together genetically divergent source populations, resulting in genetic admixture. This geographic reshuffling of diversity has the potential to generate favourable new genetic combinations, facilitating the establishment and invasive spread of introduced populations. Observational support for the superior performance of admixed introductions has been mixed, however, and the broad importance of admixture to invasion questioned. Under most underlying mechanisms, admixture's benefits should be expected to increase with greater divergence among and lower genetic diversity within source populations, though these effects have not been quantified in invaders. We experimentally crossed source populations differing in divergence in the invasive plant Centaurea solstitialis. Crosses resulted in many positive (heterotic) interactions, but fitness benefits declined and were ultimately negative at high source divergence, with patterns suggesting cytonuclear epistasis. We explored the literature to assess whether such negative epistatic interactions might be impeding admixture at high source population divergence. Admixed introductions reported for plants came from sources with a wide range of genetic variation, but were disproportionately absent where there was high genetic divergence among native populations. We conclude that while admixture is common in species introductions and often happens under conditions expected to be beneficial to invaders, these conditions may be constrained by predictable negative genetic interactions, potentially explaining conflicting evidence for admixture's benefits to invasion. [ABSTRACT FROM AUTHOR]

Abstract: Many plant invasion studies in grasslands suggest that resident plants that share functional traits with invaders can reduce invasion by competing for limiting resources. However, since invasion studies often occur in highly controlled plots or microcosms, it is unclear how heterogeneous site conditions alter competitive interactions under realistic scenarios. To explore how landscape heterogeneity affects biotic resistance provided by competitive resident plants, we conducted a field‐based experiment across four sites in California grasslands. Plots contained naturally occurring populations of native Hemizonia congesta, but differed in other characteristics, including litter cover, annual grass cover, soil moisture, and species richness. We invaded plots with the functionally similar nonnative Centaurea solstitalis (yellow starthistle) and, at one site, supplemented one‐half of the established plots with water to test the effects of increasing a limiting resource. As in simplified plots and microcosms, increasing H. congesta abundance reduced starthistle biomass by competing for limited soil moisture, but only in plots with high starthistle germination. We conclude that higher abundances of native H. congesta can reduce starthistle invasion in heterogeneous grasslands, but competition is also affected by both abiotic (soil moisture) and biotic (starthistle germination number) conditions that vary across sites. [ABSTRACT FROM AUTHOR]

The historical management of agroecological systems, such as California's rangelands, have received criticism for a singular focus on agricultural production goals, while society has shifting expectations to the supply of multiple ecosystem services from these working landscapes. The sustainability and the multiple benefits derived from these complex social-ecological systems is increasingly threatened by weed invasion, extreme disturbance, urban development, and the impacts of a rapidly changing and increasingly variable climate. California's grasslands, oak savannas, and oak woodlands are among the most invaded ecosystems in the world. Weed eradication efforts are rarely combined with seeding on these landscapes despite support for the inclusion of the practice in a weed management program. Depending on seed mix choice, cost and long-term uncertainty, especially for native seed, is an impediment to adoption by land managers. We investigated four seeding mixes (forage annual, native perennial, exotic perennial, and exotic-native perennial) to evaluate how these treatments resist reinvasion and support the delivery of simultaneous multiple ecosystem services (invasion resistance, native richness, nitrogen fixing plants, pollinator food sources, plant community diversity, forage quality, and productivity). We found the increase of exotic and native perennial cover will drive resistance to an invading weedy summer flowering forb Centaurea solstitialis but provides a mixed response to resisting invasive annual grasses. The resistance to invasion is coupled with little tradeoff in forage productivity and quality and gains in plant diversity and native cover. [ABSTRACT FROM AUTHOR]

Centaurea solstitialis L. (yellow starthistle, Asteraceae) is a Eurasian native plant introduced as an exotic into North and South America, and Australia, where it is regarded as a noxious invasive. Changes in ploidy level have been found to be responsible for numerous plant biological invasions, as they are involved in trait shifts critical to invasive success, like increased growth rate and biomass, longer life-span, or polycarpy. C. solstitialis had been reported to be diploid (2n = 2x = 16 chromosomes), however, actual data are scarce and sometimes contradictory. We determined for the first time the absolute nuclear DNA content by flow cytometry and estimated ploidy level in 52 natural populations of C. solstitialis across its native and non-native ranges, around the world. All the C. solstitialis populations screened were found to be homogeneously diploid (average 2C value of 1.72 pg, SD = ±0.06 pg), with no significant variation in DNA content between invasive and non-invasive genotypes. We did not find any meaningful difference among the extensive number of native and non-native C. solstitialis populations sampled around the globe, indicating that the species invasive success is not due to changes in genome size or ploidy level.

How variation in factors controlling species abundance and distribution between native and non-native ranges compares to that within ranges remains poorly understood. We used a globally distributed ruderal, Centaurea solstitialis ( Centaurea), to explore the possibility that the importance of those factors exhibits great variation between and within ranges. To test our hypothesis, we established seed addition experiments with soil disturbance (turnover and control) and biocide (fungicides, insecticide, and control) treatments in two regions within native (the Caucasus and south-western Turkey) and non-native (the western United States - US - and central Argentina) distributions. Also, we estimated the rate of vegetation recovery after disturbance (resilience) and related it to Centaurea density in experimental plots. Disturbance strongly increased Centaurea density in all regions. Density was similar between the native Caucasus and non-native Argentina and much greater in those regions than in the native Turkey and non-native US in biocide-free plots. Fungicides had positive effects on density in the US and negative ones in the Caucasus and Argentina, resulting in no differences between those three regions and greater density in the US than Turkey. Insecticide applications promoted Centaurea density in Turkey and Argentina, but inter-regional comparisons of density in treated plots were comparable to those in biocide-free plots. Overall, plants were smaller and less fecund in Turkey than the other regions, except the US. The greatest fungal attack was documented in Turkey, and herbivory was stronger there and in Argentina than in the Caucasus and US. The resilience of the local community explained a large proportion of variation in Centaurea density. These results support our hypothesis, and reveal that the speed at which competition is re-gained after disturbance may influence global variation in Centaurea abundance. Because many ruderals exhibit native and non-native distributions, our results are likely to be generalized to other systems. [ABSTRACT FROM AUTHOR]

Yellow starthistle ( Centaurea solstitialis L) ( YST) is an invasive weed native to the Mediterranean region with a geographical centre of diversity in Turkey. It is widely established in Chile, Australia, and western North America. It arrived in California as a contaminant in alfalfa seed in 1859 and, by 2002, had infested >7.7 million hectares in the U.S.A., Biological control of YST using capitula feeding weevils, picture wing flies and a foliar rust pathogen has been ongoing in the western U.S.A. for more than three decades with limited success. Modelling and field research suggest natural enemies that kill whole plants and/or reduce seed production of survivors are good candidates for successful biological control. A candidate species with some of these attributes is the rosette weevil Ceratapion basicorne ( Illiger)., In the present study, a model of the rosette weevil is added to an extant system model of YST and its capitula feeding natural enemies and, in a GIS context, is used to assess YST control in the Palearctic region and the weevil's potential impact on YST in western U.S.A., The results obtained suggest densities of mature YST plants in western U.S.A. would be reduced by 70-80% in many areas. [ABSTRACT FROM AUTHOR]

A 2-yr (2014-2015) field study in eastern Washington State quantified the effect of environmental factors on the overwintered Eustenopus villosus (Boheman) and Larinus curtus (Hochhut) adults in relation to phenology of Centaurea solstitialis L. (Asteraceae: Cardueae), the feeding and breeding host for these two weevil biocontrol agents. We recorded in the study area: ambient and soil temperatures, soil moisture, percent cover and developmental stage of C. solstitialis, and presence of adults of each weevil species. Sampling took place from early May to mid-August. Weevil activity for both species in both years was segregated into three phases: 1 - a pre-appearance phase in which neither species was detected, 2 - appearance and increase in frequency, and 3 - decrease in frequency. Eustenopus villosus increase in frequency was most strongly associated with warming temperatures both years. Larinus curtus increase in frequency in 2014 was most associated with increasing C. solstitialis cover and in 2015 with warming temperatures and drying soils. In both years, both weevil species' decline in frequency was likely due to the advancing C. solstitialis phenology. This pattern indicates that the appearance and increase in frequency of the overwintered E. villosus and L. curtus adults was likely a function of warming temperatures. Both species' decline in frequency was likely a function of the weevils completing their life cycle in synchrony with the phenological advancement of C. solstitialis and decline of abundant breeding and foraging sites (buds and flowers). [ABSTRACT FROM AUTHOR]

Successful colonization by invasive species depends on both the ability to disperse seeds to a site and an ability to establish once seeds have arrived. While seed and establishment limitation are known to jointly influence colonization, decomposing establishment limitation into density-dependent and density-independent components has remained challenging., Here, we couple theoretical models of recruitment with a multispecies invasion experiment conducted within a natural gradient of soil moisture and productivity to assess how variation in establishment limitation shapes outcomes for invasion., Recruitment was affected by both density-dependent and density-independent sources of establishment limitation in three of four species. Soil moisture stress and productivity both increased density-independent mortality in one species, whereas density-dependent mortality increased in locations with favourable soil moisture., Synthesis. Successful establishment of invading species can be limited by both density-dependent and density-independent mechanisms. In particular, the strength of density-independent limitation may depend on natural gradients in abiotic factors. The varying strengths of establishment limitation suggest that patterns of invasion are likely to be uneven both in space and in time. Understanding how intraspecific competitive constraints and density-independent limitation vary with abiotic gradients can assist with predicting when invasions are likely to occur, information that can be harnessed in the development of better methods for control. [ABSTRACT FROM AUTHOR]

Identifying sources of genetic variation and reconstructing invasion routes for non-native introduced species is central to understanding the circumstances under which they may evolve increased invasiveness. In this study, we used genome-wide single nucleotide polymorphisms to study the colonization history of Centaurea solstitialis in its native range in Eurasia and invasions into the Americas. We leveraged this information to pinpoint key evolutionary shifts in plant size, a focal trait associated with invasiveness in this species. Our analyses revealed clear population genomic structure of potential source populations in Eurasia, including deep differentiation of a lineage found in the southern Apennine and Balkan Peninsulas and divergence among populations in Asia, eastern Europe and western Europe. We found strongest support for an evolutionary scenario in which western European populations were derived from an ancient admixture event between populations from eastern Europe and Asia, and subsequently served as the main genetic 'bridgehead' for introductions to the Americas. Introductions to California appear to be from a single source region, and multiple, independent introductions of divergent genotypes likely occurred into the Pacific Northwest. Plant size has evolved significantly at three points during range expansion, including a large size increase in the lineage responsible for the aggressive invasion of the California interior. These results reveal a long history of colonization, admixture and trait evolution in C. solstitialis, and suggest routes for improving evidence-based management decisions for one of the most ecologically and economically damaging invasive species in the western United States. [ABSTRACT FROM AUTHOR]

Several studies have revealed a variety of mechanisms of invasion of alien plant species. However, little is known on how those mechanisms and their associated effects on native species change across different life-cycle stages. Under controlled conditions, we assessed the interactions between the alien invasive species Centaurea solstitialis L. (Asteraceae) and two pioneer native species to the Chilean matorral; Baccharis linearis (Ruiz et Pav.) Pers. and B. paniculata DC. (Asteraceae). Competitive effects of the invader on natives were evaluated by combining different life-cycle stages: seed-seed, plant-seed, and plant-plant. Seed germination of C. solstitialis was explosive and much faster than that of the native species. The presence of C. solstitialis (individuals or seeds) did not affect negatively the seed germination of the two Baccharis species. However, the presence of C. solstitialis plants significantly decreased the total biomass oí Baccharis plants. Thus, the effect of C. solstitialis on Baccharis species depended on the life-cycle stage at which the interactions occurred. In the Chilean matorral, the early emergence of C. solstitialis could be an important invasion mechanism, enabling established plants to competitively displace late emerging seedlings of Baccharis species. The huge abundance of C. solstitialis in some disturbed matorrals suggests that seedling establishment of these two pioneer species could be limited.Varios estudios han revelado una variedad de mecanismos de invasión en las plantas alóctonas. Sin embargo, aún se conoce poco sobre cómo tales mecanismos y sus efectos asociados cambian a través de diferentes estados del ciclo vida. En este estudio evaluamos, bajo condiciones controladas, el resultado de las interacciones competitivas entre la especie invasora Centaurea solstitialis L. (Asteraceae) y dos especies pioneras nativas del matorral chileno; Baccharis linearis (Ruiz et Pav.) Pers. y B. paniculata DC (Asteraceae). Estas interacciones fueron evaluadas combinando diferentes estados del ciclo de vida: semilla-semilla, planta-semilla y planta-planta. La germinación de C. solstitialis fue explosiva, siendo mucho más rápida que la de las especies nativas. La presencia de C. solstitialis (plantas o semillas) no disminuyó la germinación de las especies nativas de Baccharis. Sin embargo, la presencia de plantas establecidas de C. solstitialis disminuyó significativamente la biomasa de las plantas de Baccharis. Entonces, el efecto de C. solstitialis sobre las especies de Baccharis varió en función del estado del ciclo de vida en el cual las interacciones ocurrieron. En el matorral chileno, la emergencia temprana y explosiva de C. solstitialis podría ser un importante mecanismo de invasión, ya que aquellas plantas prontamente establecidas podrían desplazar competitivamente a las plántulas de Baccharis que emergen más tarde. La enorme abundancia de C. solstitialis en algunas zonas de matorral sugiere que el establecimiento de plántulas de estas dos especies pioneras podría estar siendo limitado.

Most remote sensing approaches for mapping invasive plant species focus on species in a prominent phenological stage, such as during flowering, and do not systematically evaluate the performance for mapping lower cover fractions. In this study, we used airborne imaging spectroscopy (also known as hyperspectral imaging) to detect the invasive grass Phalaris aquatica and the invasive herb Centaurea solstitialis in a pre-flowering stage in the Jasper Ridge Biological Preserve, California, and compared the performance of three different one-class classifiers: Maxent, biased support vector machines and boosted regression trees. We collected presence data for C. solstitialis and P. aquatica to calibrate each approach and additional presence-absence data to validate model performance on 3 m × 3 m plots. The imaging spectroscopy data were acquired using the Carnegie Airborne Observatory Visible-to-Shortwave Infrared (VSWIR) imaging spectrometer (400–2500 nm range) with a pixel size of 1 m × 1 m. The resulting overall accuracies were 72–74% for C. solstitialis , and 83–88% for P. aquatica . For both species, the overall performance was slightly better for Maxent and BRT than for biased SVM. The detection rates for low cover plots were considerably higher for C. solstitialis than for P. aquatica . The models relied on different areas of the reflectance spectrum, but still produced the same general pattern of predicted species occurrences. We conclude that the different one-class classifiers allow for the detection and monitoring of target species with similar success rates. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal ( AM) fungi can exert a powerful influence on the outcome of plant-plant competition. Since some exotic plants interact differently with soil biota such as AM fungi in their new range, range-based shifts in AM responsiveness could shift competitive interactions between exotic and resident plants, although this remains poorly studied., We explored whether genotypes of the annual exotic Centaurea solstitialis (yellow starthistle), collected from populations across the native and non-native ranges, differed in responsiveness to AM fungi in the introduced range and whether range-based differences in mycorrhizal responsiveness affected how strongly C. solstitialis tolerated competition with the North American native bunchgrass, Stipa pulchra., Grown alone, C. solstitialis from both ranges derived only weak benefits from AM fungi. However, association with AM fungi was costly to plants when grown in competition with S. pulchra. The magnitude of the suppressive effect of AM fungi was greater for genotypes from native versus introduced populations., Synthesis. Many exotic invasive species are known to associate weakly with AM fungi, which may be beneficial in disturbed habitats where competition for resources is low. Our results indicate that reduced mycorrhizal associations may also benefit invaders in a competitive environment. Centaurea solstitialis were more strongly suppressed by established S. pulchra plants in the presence versus absence of AM fungi, but exotic genotypes were less suppressed than native genotypes. This suggests that AM fungi may contribute to invasion resistance in established native communities, but range-based shifts in the way exotic genotypes respond to AM fungal partners may counter such biotic resistance. [ABSTRACT FROM AUTHOR]

Successful exotic plant invasions are likely to be caused by multiple, non-mutually exclusive mechanisms, and it is exceptionally difficult to weight the relative importance of these mechanisms identified in different experiments. To this end we used individual-based models to explore how integrating empirical results from experiments might help to elucidate the relative importance of seed origin, biogeographic differences in competitive outcomes, and disturbance in exotic plant invasion. We integrated results from (1) competition experiments between Centaurea solstitialis derived from populations in the non-native range (California), the native range (Spain), and co-occurring native species from both ranges, (2) seed production by Centaurea plants from the different ranges grown in a common-garden environment, and (3) responses to disturbance experiments with plants from different native and non-native ranges. Californian C. solstitialis reached slightly higher abundances than its Spanish counterparts in every scenario, mainly due to higher seed production of Californians than their Spanish conspecifics, indicating the potential importance of evolutionary changes in the non-native range. In the absence of disturbance, grass species native to Europe showed stronger competitive effects on C. solstitialis than grass species native to North America, suggesting that release from competition in the native range may have some explanatory power for successful C. solstitialis invasion. However, the intensity of competition depended on the disturbance regime used in models. When intense disturbance was incorporated into the model, C. solstitialis was favored, with plants from Californian seed sources reaching higher densities than plants from Spanish seed sources. Our results are consistent with the idea that disproportional positive responses to disturbance in California, relative to those in the invader's native range of Spain, may be an important factor in the dominance of C. solstitialis in its non-native ranges. It is not clear why disturbance would have more beneficial effects on the invader in its non-native range, but the powerful effects of disturbance appear to interact in subtle ways with biogeographic differences in evolutionary trends, competitive intensities, life histories, and reproductive rates. [ABSTRACT FROM AUTHOR]

Plant chemical defenses can be qualitative (toxins) to face generalist herbivores and quantitative (digestibility reducers) to specialists. Trichomes can produce chemicals, but also acts as a quantitative defense and in water loss. The shifting defense hypothesis (SDH) poses that invasive plants reduce the production of qualitative defenses against specialist herbivores because those are frequently absent in invaded regions, while increasing defenses against generalist herbivores. Chemical and physical leaf surface defensive traits could give information about direct plant–herbivore interaction in native and non-native regions. We studied leaf surface morphology and epicuticular chemistry of the invasive C. solstitialis in plants from native and non-native regions. Across regions, the main chemical components were sesquiterpene lactones, similar densities of sessile glandular trichomes and a variable number of large multicellular trichomes. Exotic plants face different sets of challenges in the new regions. In accordance with SDH, plants from non-native regions presented higher total sesquiterpene lactones concentrations (qualitative defense). Trichome density was possibly associated to differences in local climatic conditions. Sesquiterpene lactones are likely to play an important role on the invasion success of Centaurea . Leaf surface components provide meaningful information that should be consider in future studies to unravel the mechanisms involved in plant invasions. [ABSTRACT FROM AUTHOR]

The natural history of introduced species is often unclear due to a lack of historical records. Even when historical information is readily available, important factors of the invasions such as genetic bottlenecks, hybridization, historical relationships among populations and adaptive changes are left unknown. In this study, we developed a set of nuclear, simple sequence repeat markers and used these to characterize the genetic diversity and population structure among native (Eurasian) and non-native (North and South American) populations of Centaurea solstitialis L., (yellow starthistle). We used these data to test hypotheses about the invasion pathways of the species that were based on historical and geographical records, and we make inferences about historical relationships among populations and demographic processes following invasion. We confirm that the center of diversity and the native range of the species is likely the eastern Mediterranean region in the vicinity of Turkey. From this region, the species likely proceeded to colonize other parts of Europe and Asia via a slow, stepwise range expansion. Spanish populations were the primary source of seed to invade South America via human-mediated events, as was evident from historical records, but populations from the eastern Mediterranean region were also important. North American populations were largely derived from South America, but had secondary contributors. We suggest that the introduction history of non-native populations from disparate parts of the native range have allowed not just one, but multiple opportunities first in South America then again in North America for the creation of novel genotypes via intraspecific hybridization. We propose that multiple intraspecific hybridization events may have created especially potent conditions for the selection of a noxious invader, and may explain differences in genetic patterns among North and South America populations, inferred differences in demographic processes, as well as morphological differences previously reported from common garden experiments. [ABSTRACT FROM AUTHOR]

Ecological filter models derived from community assembly theory can inform restoration planning by highlighting management actions most likely to affect community composition. Despite growing interest in these models, many restoration studies solely manipulate a single assembly filter - the biotic filter by altering interspecific competition - while ignoring abiotic and dispersal filters that may also influence restoration success., To examine how manipulating all three assembly filters (biotic, abiotic, dispersal) affected restoration in an annual-type grassland, we seeded native forbs from the same functional group as a target invader to increase biotic resistance to invasion (biotic filter), cut standing biomass and either removed it or returned it to plots as litter to alter light conditions (abiotic filter), and added native forbs at different seeding rates to alter density of establishing native populations (dispersal filter). We measured grassland restoration success by recording native species and invader cover in plots., The addition of native species with phenological and morphological traits similar to the target invader reduced invasion and increased native populations, but only in litter-free plots when high densities of native seed were added., Seeding two species with functional traits similar to the invader was more effective for achieving restoration goals than seeding just one functionally similar species. As such, trait differences among restoration species, even species belonging to the same functional group, may increase biotic resistance to invasion in restored communities., Litter removal altered native-invader interactions. When litter was left on the plots, added natives did not reduce invader cover. However, when litter was removed, added natives led to declines in invader cover., Increasing native seeding rates led to larger native populations and increased invasion resistance., Synthesis and applications. In this study, simultaneously manipulating biotic, abiotic and dispersal filters was necessary to optimize grassland restoration outcomes. In particular, the biotic filter only contributed to successful restoration outcomes under abiotic and dispersal conditions that were created through management actions specifically targeting these two additional filters. Restoration planning based on filter models should incorporate actions that target all three assembly filters, rather than solely focusing on the biotic filter. [ABSTRACT FROM AUTHOR]

Centaurea solstitialis (yellow starthistle) has invaded rangelands and natural areas in the western USA. There is evidence that mowing is a more effective method of reducing growth and seed production, compared with the well-established and distributed bioagents. To test this hypothesis we measured C. solstitialis's growth and reproduction following two treatments (late spring and early summer bud/capitula destruction and shoot mowing) and measured C. solstitialis's growth and reproduction. We measured changes in soil moisture content to test the hypothesis that these manipulations differentially affect water usage by the invasive plant. Mowing produced shorter plants that weighed less. Bud damaged plants were not statistically different from untreated controls. The number of developed capitula was reduced 67% by mowing but was unaffected by bud damage. Mowed plants redistributed resources from root to flower production. Both treatments reduced mean capitulum diameter. This resulted in reductions of 76% and 21% in estimated seed number for mowed and bud damaged plants respectively. Root abundance decreased and root life-span was reduced by both treatments. Soil moisture depletion was greatest from mid-May to mid-July (from 21% to 9%) and occurred after maximum root abundance. Mowing resulted in a delay in soil moisture depletion compared with the bud damaged plants or the untreated controls. Bud/capitula damage did not affect C. solstitialis's requirement for soil water. Overall, this study supported the hypothesis that mowing reduced C. solstitialis growth and reproduction more than bud damage alone. This information will aid managers in selecting a strategy for managing C. solstitialis in a particular habitat. [ABSTRACT FROM AUTHOR]

Herbivore damage often deters pollinator visitation and many invasive plants in North America are pollinator-dependent. This has important implications for the biological control of invasive plants because it means that agents that deter pollinators may have a larger than expected impact on the plant. Yet interactions between pollinators and biocontrol agents are rarely evaluated. Centaurea solstitialis, one of the most problematic invasive species in California, is dependent on pollinators for reproduction. I factorially manipulated infection by a biocontrol pathogen and pollen supplementation to test for (1) pollen limitation in C. solstitialis, (2) whether infection increased pollen limitation, and (3) whether this varied across a soil moisture gradient. Plants growing on north-facing slopes where soil moisture was higher experienced mild pollen limitation in the absence of the pathogen and more pronounced pollen limitation when they were infected. Plants on drier south-facing slopes did not suffer from pollen limitation but instead appeared to suffer from resource limitation. Pathogen infection directly reduced seed set in C. solstitialis by 67-72 %. On north-facing slopes, infection had an additional, indirect effect by increasing the degree of pollen limitation plants experienced. The trait that mediates this indirect pathogen-pollinator interaction is the number of inflorescences plants produced: infected plants made fewer inflorescences which led to greater pollen limitation. Although in the present study this outcome is dependent on abiotic factors that vary over small spatial scales, exploiting other invasive plants' dependence on pollinators by selecting agents that deter visitation may enhance agent impact. [ABSTRACT FROM AUTHOR]

Pollinator-plant relationships are found to be particularly vulnerable to land use change. Yet despite extensive research in agricultural and natural systems, less attention has focused on these interactions in neighboring urban areas and its impact on pollination services. We investigated pollinator-plant interactions in a peri-urban landscape on the outskirts of the San Francisco Bay Area, California, where urban, agricultural, and natural land use types interface. We made standardized observations of floral visitation and measured seed set of yellow starthistle (Centaurea solstitialis), a common grassland invasive, to test the hypotheses that increasing urbanization decreases 1) rates of bee visitation, 2) viable seed set, and 3) the efficiency of pollination (relationship between bee visitation and seed set). We unexpectedly found that bee visitation was highest in urban and agricultural land use contexts, but in contrast, seed set rates in these human-altered landscapes were lower than in natural sites. An explanation for the discrepancy between floral visitation and seed set is that higher plant diversity in urban and agricultural areas, as a result of more introduced species, decreases pollinator efficiency. If these patterns are consistent across other plant species, the novel plant communities created in these managed landscapes and the generalist bee species that are favored by human-altered environments will reduce pollination services. [ABSTRACT FROM AUTHOR]

Abstract: Ceratapion basicorne is a prospective biological control agent of yellow starthistle (Centaurea solstitialis), which is an invasive alien weed in the USA. Although the weevil has a strong preference for yellow starthistle, it has been reported to develop sometimes on safflower in larval transfer and no-choice experiments. Although safflower was not attacked by this insect in previous field experiments, a release permit was denied because of concern for risk to safflower. Adult C. basicorne were released in a field experiment in which two varieties of safflower were grown in solid blocks on either side of a small number of yellow starthistle plants. Plants were dissected at the time of weevil pupation. Immature insects were reared to adult stage on artificial diet or were preserved in acetone to identify by molecular genetic analysis. C. basicorne infested 54% of the yellow starthistle plants and 0% of 1021 safflower plants. A different weevil, Ceratapion orientale, infested 1.5% of the safflower plants. These results corroborate two other published field studies in which C. basicorne was not reared from safflower. The combined results of nine experiments provide a point estimate that the probability of attack is less than 0.00059, with 99.9% confidence that it is less than 0.0045. The consistency of results from field experiments in three countries and the absence of any report of this insect being reared from safflower in the field in the weevil’s native range support the conclusion that this insect poses no significant risk to safflower. [Copyright &y& Elsevier]

The article offers information on the interactions among the biocontrol agents, pollinators, and an invasive weed. It discusses the impact of herbivores, seed predators, and pollinators on their host plants. It further mentions the importance of biological control of invasive plants as most invaders are attacked by their multiple agents.

Ceratapion basicorne is a weevil native to Europe and western Asia that is being evaluated as a prospective classical biological control agent of Centaurea solstitialis (yellow starthistle) in the United States. Choice oviposition experiments were conducted under laboratory conditions to help assess host-plant specificity of the insect. Mean oviposition rates were highest on C. solstitialis (66% of eggs, on a per replicate basis) followed by Centaurea cyanus (bachelor's button 22%), Centaurea melitensis (6%), Centaurea americana (1%), Saussurea americana (3%) and Carthamus tinctorius (safflower 2%). Adult feeding damage followed a similar pattern; however, there was less oviposition relative to the amount of adult feeding on each of the non-target species than on the target host plant, C. solstitialis. Thirteen safflower varieties were tested, and oviposition occurred on eight of them, at low rates. Adult feeding occurred on all safflower varieties tested, although at rates much lower than on yellow starthistle. The results were intermediate between those of previously reported no-choice laboratory and open field experiments. Overall, the combined results support the hypothesis that C. basicorne is not likely to attack any of the non-target plant species tested here except possibly C. cyanus and C. melitensis, which are both invasive alien plants. [ABSTRACT FROM PUBLISHER]

Aim Our aim in this study was to document the global biogeographic variation in the effects of soil microbes on the growth of Centaurea solstitialis (yellow starthistle; Asteraceae), a species that has been introduced throughout the world, but has become highly invasive only in some introduced regions. Location To assess biogeographic variation in plant-soil microbe interactions, we collected seeds and soils from native Eurasian C. solstitialis populations and introduced populations in California, Argentina and Chile. Methods To test whether escape from soil-borne natural enemies may contribute to the success of C. solstitialis, we compared the performance of plants using seeds and soils collected from each of the biogeographic regions in greenhouse inoculation/sterilization experiments. Results We found that soil microbes had pervasive negative effects on plants from all regions, but these negative effects were significantly weaker in soils from non-native ranges in Chile and California than in those from the non-native range in Argentina and the native range in Eurasia. Main conclusions The biogeographic differences in negative effects of microbes in this study conformed to the enemy-release hypothesis (ERH) overall, but the strong negative effect of soil biota in Argentina, where C. solstitialis is invasive, and weaker effects in Chile where it is not, indicated that different factors influencing invasion are likely to occur in large scale biogeographic mosaics of interaction strengths. [ABSTRACT FROM AUTHOR]

Chronic ingestion of yellow star thistle (Centaurea solstitialis) or Russian knapweed (Acroptilon repens) causes nigropallidal encephalomalacia (NPE) in horses with an abrupt onset of neurologic signs characterized by dystonia of lips and tongue, inability to prehend food, depression, and locomotor deficits. The objectives of this study were to reexamine the pathologic alterations of NPE and to conduct an immunohistochemistry study using antibodies to tyrosine hydroxylase and α-synuclein, to determine whether NPE brains show histopathologic features resembling those in human Parkinson disease. Results confirm that the NPE lesions are located within the substantia nigra pars reticulata, sparing the cell bodies of the dopaminergic neurons in the substantia nigra pars compacta, and in the rostral portion of the globus pallidus, with partial disruption of dopaminergic (tyrosine hydroxylase–positive) fibers passing through the globus pallidus. No abnormal cytoplasmic inclusions like the Lewy bodies of human Parkinson disease were seen in these NPE brains. These findings indicate that equine NPE may serve as a large animal model of environmentally acquired toxic parkinsonism, with clinical phenotype directly attributable to lesions in globus pallidus and substantia nigra pars reticulata rather than to the destruction of dopaminergic neurons. [ABSTRACT FROM PUBLISHER]

The effects of declining plant biodiversity on ecosystem processes are well studied, with most investigations examining the role of species richness declines rather than declines of species abundance. Using grassland mesocosms, we examined how the abundance of a native, resident species, Hemizonia congesta (hayfield tarweed), affected exotic Centaurea soistitialis (yellow starthistle) invasion. We found that progressive H. congesta abundance declines had threshold effects on invasion resistance, with initial declines resulting in minor increases in invasion and subsequent declines leading to accelerating increases in invader performance. Reduced invasion resistance was explained by increased resource availability as H. congesta declined. We also found evidence that resident abundance might indirectly affect invasion by mediating invader impact on resident competitors; C. solstiiialis disproportion- ately reduced H. congesta biomass in low-abundance rather than high-abundance populations. H. congesta's direct and indirect effects on invasion resistance illustrate that an individual species' declining abundance can have accelerating, deleterious effects on ecosystem functions of conservation value. [ABSTRACT FROM AUTHOR]

Abstract: Host range determination is essential to risk assessments of classical biological weed control agents and needed for petitions to release of agents into non-native areas. Recently Henderson’s mixed model equations (MME) were adapted to evaluating host ranges of two biological control pathogens. This was accomplished by incorporating genetic relatedness, in the form of DNA sequences, with disease evaluation data among target and non-target plants to generate best linear unbiased predictors (BLUPs) of disease reaction among these plant species. Although qualities of MME analysis provide inherent validation of the approach, it has been difficult to validate by comparison with historical host range determination or field data. These types of data are virtually non-existent, because original, raw host range data from replicated tests have, for the most part, been lost, and host-range data from tests or monitoring of multiple plant species in the field are extremely limited. In this study, the host-ranges of two biological weed control pathogens previously released in the USA were re-evaluated with the MME and historical host-range data. Results showed that: BLUPs confirmed the narrow host range of the two pathogens; BLUPs supported and substantiated currently available information on host range; BLUPs were accurate predictors of host range, particularly concerning susceptibility of any non-target species in the field; and no new, unforeseen non-target effects could be expected in nature on the basis of BLUPs. Thus, validation was made for MME analysis in predicting known field host-range from greenhouse data. [Copyright &y& Elsevier]

A three-year study was conducted in the Chihuahuan Desert in Southwestern New Mexico to evaluate the effectiveness of revegetating a dryland pasture that was heavily infested with yellow starthistle within the context of the successional weed management model. A prescribed burn treatment of the entire study site (designed disturbance) was followed by single-entry revegetation (controlled colonization) and weed suppression (controlled species performance) treatments. Four native perennial grass species were paired with 4 yellow starthistle suppression treatments. We conclude that an integrated, single-entry approach failed to effectively revegetate yellow starthistle-infested dryland pasture in the Chihuahuan Desert, primarily due to a historic severe drought that occurred soon after grasses were seeded. Different strategies and tactics will be required to manage yellow starthistle in the Southwestern USA than have been previously applied in other areas. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the effects of biocontrol agent Eustenopus villosus on Centaurea solstitialis weed with and without generalist parasitoid Pyemotes tritici. It mentions the use of demographic data in assessing how the weed populations from different climatic zones might respond differently to the agent and parasitoid. Results indicate that the agent did not have long-term effect on the weed population growth rate.

Centaurea solstitialis (yellow starthistle, Asteraceae) is an invasive annual weed in the western USA that is native to the Mediterranean Region and is a target for classical biological control. Aceria solstitialis is an eriophyid mite that has been found exclusively in association with Ce. solstitialis in Italy, Greece, Turkey and Bulgaria. The mite feeds on leaf tissue and damages bolting plants, causing stunting, witch's broom and incomplete flower development. Field experiments and laboratory no-choice and two-way choice experiments were conducted to assess host plant specificity of the mite in Bulgaria. Mites showed the highest degree of host specificity in the field and lowest in the no-choice experiments. In the field, highest densities of mites occurred on Ce. solstitialis and Ce. cyanus (bachelor's button), and either no mites or trace numbers occurred on the other test plants: Ce. diffusa (diffuse knapweed), Carthamus tinctorius (safflower) and Cynara scolymus (artichoke). In no-choice experiments, mites persisted for 60 days on Ce. diffusa, Ce. cyanus, Ce. solstitialis, Ca. tinctorius and Cy. scolymus, whereas in two-way choice experiments mites persisted on 25% of Cy. scolymus plants for 60 days and did not persist on Ca. tinctorius beyond 40 days. The eight other species of plants that were tested in the laboratory were less suitable for the mite. These results suggest that although A. solstitialis can persist on some nontarget plants for as long as 60 days in the laboratory, it appears to be much more specific under natural conditions, and warrants further evaluation as a prospective biological control agent. [ABSTRACT FROM AUTHOR]

Background and Aims: Seeds buried in the soil detect burial depth through light and diurnally fluctuating temperatures (DFT) and in this way limit losses due to germination too deep in the soil. DFTs and germination also increase in vegetation gaps. However, dry open environments with high DFTs can also increase seedling mortality, creating conflicting selection pressures for reaction to DFTs. Since this questions the general function of DFT detection, we therefore tested if interspecific differences in DFT detection are related to mortality in different soil depths. Methods: We buried seeds of ten annual plants including species pairs of increasing and decreasing germination in response to DFTs. Seeds were buried in 5, 10 and 25cm soil depth and exhumed after two different burial times. Seed viability was tested using germination in growth chambers and tetrazolium. We also measured DFTs at these depths using temperature data loggers. Results: DFT detection was not related to differences in mortality at three burial depths. Three species showed a clear pattern of depth dependent mortality, however inconsistently related to DFT detection. Conclusions: Depth detection mechanisms are more species-specific than expected. Hence, interspecific differences in seed mortalities are difficult to predict by DFT detection alone and alternative soil depth sensing mechanisms should be explored in future. [ABSTRACT FROM AUTHOR]

BACKGROUND: Aminocyclopyrachlor is a new herbicide proposed to control broadleaf weeds and shrubs in non-crop and rangeland systems. To gain a better understanding of observed field efficacy, the uptake and translocation of foliar-applied aminocyclopyrachlor (DPX-MAT28) and aminocyclopyrachlor methyl ester (DPX-KJM44) were evaluated in two annuals, prickly lettuce ( Lactuca serriola L.) and yellow starthistle ( Centaurea solstitialis L.), and one perennial, rush skeletonweed ( Chondrilla juncea L.). RESULTS: Absorption and translocation varied between species. While absorption of DPX-KJM44 was greater than absorption of DPX-MAT28, rush skeletonweed absorbed the most, followed by yellow starthistle and prickly lettuce. Overall, the total translocation of either herbicide was highest in yellow starthistle, followed by rush skeletonweed and prickly lettuce. Proportional herbicide movement between species was similar, with the majority translocating to developing shoots. However, in rush skeletonweed, early translocation was directed to root tissue. In rush skeletonweed, no DPX-MAT28 metabolism occurred, while DPX-KJM44 was rapidly de-esterified and translocated as DPX-MAT28. CONCLUSION: Aminocyclopyrachlor absorption and translocation are dependent on active ingredient structure and species sensitivity. Highly sensitive species such as prickly lettuce absorb and translocate less material than relatively less sensitive species such as rush skeletonweed. De-esterification of DPX-KJM44 appears to delay translocation of the resulting acid in yellow starthistle and rush skeletonweed. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]