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Subsequent to escape from intense herbivory in the native range, invasive plants are expected to reduce allocation to costly anti‐herbivory defences and have greater competitive ability than co‐occurring native species. Given that invasive alien plants often occur in open habitats where light is less limited, it is reasonable to hypothesize that invasive plants should express high concentrations of gibberellins that enable them to allocate more biomass to roots, and thus have higher competitive ability than native plants. To test this prediction, we grew five congeneric pairs of invasive alien plants and native plants under two levels of nutrient availability (low versus high) and treated a half of the plants with a gibberellin biosynthesis inhibitor, paclobutrazol. Paclobutrazol significantly decreased aboveground, belowground and total biomass of the test plants. Interestingly, the effects on belowground biomass were significantly stronger for invasive plants than for native plants. A similar pattern was found for total biomass (marginally significant effect p = 0.0592). Additionally, paclobutrazol decreased root mass fraction for invasive plants, but tended to increase it for native plants. Our findings suggest that plant hormones can differently regulate biomass allocation of invasive and native plants, and thus contribute to greater growth of invasive plants compared to native plants.

Polyploidy can cause variation in plant functional traits and thereby generate individuals that can adapt to fluctuating environments and exploit new environments. However, few empirical studies have tested for an association between ploidy level and climatic tolerance of invasive cytotypes relative to conspecific native‐range cytotypes. Here, we used an invasive plant Solidago canadensis to test whether invasive populations had a higher proportion of polyploids, greater height and stem‐base diameter, and occupied a wider range of climatic conditions than conspecific native‐range populations. We also tested whether the invasive populations had overcome genetic founder effects. We sampled a total of 80 populations in parts of the invaded range in China and native range in North America for in situ measurements of plant height and stem‐base diameter in the field and for population genetic and cytotype analyses. To examine climatic correlates, we augmented our field‐sampled data with occurrence records obtained from Global Biodiversity Information Facility. All, except one, of the populations that we sampled in China occurred in a humid subtropical climate. In contrast, the North American populations occurred in humid continental, humid subtropical, and semi‐arid climatic zones. All populations of S. canadensis in China were purely hexaploid, while the North American populations were diploid, tetraploid, and hexaploid. The invasive hexaploids were significantly taller and had a larger stem‐base diameter than native hexaploids. Native hexaploids were significantly taller and had larger stem‐base diameter than native diploids. Climatic correlate assessment found that invasive and native populations occupied different climatic envelopes, with invasive populations occurring in warmer and less seasonal climates than native populations. However, there was no significant correlation between ploidy level and climatic envelope of S. canadensis. Molecular phylogeography data suggest reduced genetic founder effects in the invaded range. Overall, these results suggest that polyploidy does not influence S. canadensis climatic tolerance.

Premise Evolutionary adaptation may enable plants to inhabit a broad range of environments. However, germination and early life-history stages have seldom been considered in estimates of evolutionary adaptation. Moreover, whether soil microbial communities can influence evolutionary adaptation in plants remains little explored. Methods We used reciprocal transplant experiments to investigate whether two populations of an invasive plant Solidago canadensis that occur in contrasting habitats of low versus high salinity expressed adaptation to the respective salinity levels. We germinated S. canadensis seeds collected from low-and high-salinity habitats under low- and high-salt treatments. We also raised S. canadensis seedlings from the two salinity habitats under low- and high-salt treatments and in the presence versus absence of microbial communities from the two habitats. Results Genotypes from a low-salinity habitat had higher germination rates under low-salt treatment than genotypes from a high-salinity habitat. However, both genotypes had similar germination rates under a high-salt treatment. The two genotypes also had similar seedling survival and biomass responses to low- and high-salt treatments. Nevertheless, seedling biomass was significantly higher under low salt treatment. Soil microbial communities did not influence biomass of S. canadensis under the two salt treatments. Conclusions The results on germination rates suggest partial local adaptation to low salinity. However, there was no evidence of local adaptation to salinity at the seedling survival and growth stages. The finding that germination and seedling biomass responded to different salt treatments suggests that the two traits are important for salt tolerance.

SummaryInvasive plant species often exhibit greater growth and lower anti-herbivory defense than native plant species. However, it remains unclear how nutrient enrichment of invaded habitats may interact with competition from resident native plants to affect growth and defense of invasive plants.In a greenhouse experiment, we grew five congeneric pairs of invasive and native plant species under two levels of nutrient availability (low vs. high) that were fully crossed with simulated herbivory (clipping vs. no-clipping) and competition (alone vs. competition).Invasive plants produced more gibberellic acid, and grew larger than native species. Nutrient enrichment caused a greater increase in total biomass of invasive plants than of native plants, especially in the absence of competition or without simulated herbivory treatment. Nutrient enrichment decreased leaf flavonoid contents of invasive plants under both simulated herbivory conditions, but increased flavonoid of native plants under simulated herbivory condition. Nutrient enrichment only decreased tannins production of invasive species under competition. For native species, it enhanced their tannins production under competition, but decreased the chemicals when growing alone.The results indicate that the higher biomass production and lower flavonoids production in response to nutrient addition may lead to competitive advantage of invasive species than native species.

Human-mediated introduction of plant and animal species into biogeographic ranges where they did not occur before has been so pervasive globally that many ecosystems are now co-invaded by multiple alien plant and animal species. Although empirical evidence of invaders modifying recipient ecosystems to the benefit of other aliens is accumulating, these interactions remain underexplored and underrepresented in heuristic models of invasion success. Many freshwater ecosystems are co-invaded by aquatic macrophytes and mollusks and at the same time experience nutrient enrichment from various sources. However, studies are lacking that test how nutrient enrichment and co-invasion by alien herbivores and plant species can interactively affect native plant communities in aquatic habitats. To test such effects, we performed a freshwater mesocosm experiment in which we grew a synthetic native macrophyte community of three species under two levels of nutrient enrichment (enrichment vs. no-enrichment) treatment and fully crossed with two levels of competition from an invasive macrophyte Myriophyllum aquaticum (competition vs. no-competition), and two levels of herbivory by an invasive snail Pomacea canaliculata (herbivory vs. no-herbivory) treatments. Results show that herbivory by the invasive snail enhanced above-ground biomass yield of the invasive macrophyte. Moreover, the invasive herbivore preferentially fed on biomass of the native macrophytes over that of the invasive macrophyte. However, nutrient enrichment reduced above-ground biomass yield of the invasive macrophyte. Our results suggest that eutrophication of aquatic habitats that are already invaded by M. aquaticum may slow down invasive spread of the invasive macrophyte. However, herbivory by the invasive snail P. canaliculata may enhance invasive spread of M. aquaticum in the same habitats. Broadly, our study underscores the significance of considering several factors and their interaction when assessing the impact of invasive species, especially considering that many habitats experience co-invasion by plants and herbivores and simultaneously undergo varous other disturbances including nutrient enrichment.

The novel-weapons and homeland-security hypotheses are based on the idea that aliens and natives are not adapted to each other’s allelochemicals as they did not co-evolve. However, as only a few studies have tested this, it remains unclear how important co-evolutionary history is in determining the strength of allelopathic interactions between aliens and natives. Here, we tested for potential pairwise allelopathic effects on each other of five alien and five native herbaceous species in China. We did a germination experiment and a competition experiment. In the germination experiment, we tested whether aqueous extracts of the ten study species had allelopathic effects on each other’s seed germination. In the competition experiment, we tested whether the alien and native species differed in their competitive effects and responses, and whether these were changed by the presence of activated carbon—a presumed allelopathy neutralizer– in the soil. Plant extracts had negative allelopathic effects on seed germination. This was particularly the case for extracts from the native species. Moreover, aqueous extracts had slightly stronger negative effects on germination of the aliens than on germination of the natives. In the competition experiment, on the other hand, the natives suffered more from competition than the alien species did, but we could not relate this to allelopathy. Alien plants had negative competitive and allelopathic effects on native plants, but the reverse was also true. These alien-native interactions, however, were not consistently stronger or weaker than native-native or alien-alien interactions.

Premise The novel-weapons hypothesis predicts that some plants are successful invaders because they release allelopathic compounds that are highly suppressive to naive competitors in invaded ranges but are relatively ineffective against competitors in the native range. For its part, the evolution of enhanced weaponry hypothesis predicts that invasive populations may evolve increased expression of the allelopathic compounds. However, these predictions have rarely been tested empirically. Methods Here, we made aqueous extracts of roots and shoots of invasive (North American) and native (European) Brassica nigra plants. Seeds of nine species from North America and nine species from Europe were exposed to these extracts. As control solutions, we used pure distilled water and distilled water with the osmotic potential adjusted with polyethylene glycol (PEG) to match that of root and shoot extracts of B. nigra. Results The extracts had a strong negative effect on germination rates and seedling root lengths of target species compared to the water-control. Compared to the osmolality-adjusted controls, the extracts had a negative effect on seedling root length. We found no differences between the effects of B. nigra plant extracts from the invasive vs. native populations on germination rates and seedling root growth of target plant species. Responses were largely independent of whether the target plant species were from the invaded or native range of B. nigra. Conclusions The results show that B. nigra can interfere with other species through allelochemical interactions, but do not support predictions of the novel-weapons hypothesis and evolution of increased allelopathy.

Invasion by exotic plant species and herbivory can individually alter native plant species diversity, but their interactive effects in structuring native plant communities remain little studied. Many exotic plant species escape from their co-evolved specialized herbivores in their native range (in accordance with the enemy release hypothesis). When these invasive plants are relatively unpalatable, they may act as nurse plants by reducing herbivore damage on co-occurring native plants, thereby structuring native plant communities. However, the potential for unpalatable invasive plants to structure native plant communities has been little investigated. Here, we tested whether presence of an unpalatable exotic invader Opuntia ficus-indica was associated with the structure of native plant communities in an ecosystem with a long history of grazing by ungulate herbivores. Along 17 transects (each 1000 m long), we conducted a native vegetation survey in paired invaded and uninvaded plots. Plots that harboured O. ficus-indica had higher native plant species richness and Shannon–Wiener diversity H′ than uninvaded plots. However, mean species evenness J was similar between invaded and uninvaded plots. There was no significant correlation between native plant diversity and percentage plot cover by O. ficus-indica. Presence of O. ficus-indica was associated with a compositional change in native community assemblages between paired invaded and uninvaded plots. Although these results are only correlative, they suggest that unpalatable exotic plants may play an important ecological role as refugia for maintenance of native plant diversity in intensely grazed ecosystems.

Invasive plants often interact with antagonists that include native parasitic plants and pathogenic soil microbes, which may reduce fitness of the invaders. However, to date, most of the studies on the ecological consequences of antagonistic interactions between invasive plants and the resident biota focused only on pairwise interactions. A full understanding of invasion dynamics requires studies that test the effects of multiple antagonists on fitness of invasive plants and co‐occurring native plants. Here, we used an invasive plant Mikania micrantha, a co‐occurring native plant Coix lacryma‐jobi, and a native holoparasitic plant Cuscuta campestris to test whether parasitism on M. micrantha interacts with soil fungi and bacteria to reduce fitness of the invader and promote growth of the co‐occurring native plant. In a factorial setup, M. micrantha and C. lacryma‐jobi were grown together in pots in the presence versus absence of parasitism on M. micrantha by C. campestris and in the presence versus absence of full complements of soil bacteria and fungi. Fungicide and bactericide were used to suppress soil fungi and bacteria, respectively. Findings show that heavy parasitism by C. campestris caused the greatest reduction in M. micrantha biomass when soil fungi and bacteria were suppressed. In contrast, the co‐occurring native plant C. lacryma‐jobi experienced the greatest increase in biomass when grown with heavily parasitized M. micrantha and in the presence of a full complement of soil fungi and bacteria. Taken together, our results suggest that selective parasitism on susceptible invasive plants by native parasitic plants and soil microorganisms may diminish competitive ability of invasive plants and facilitate native plant coexistence with invasive plants.

Summary Concerns over the ecological impacts of invasive alien plant species have generated great research interest in understanding the mechanisms that underlie the capacity of such plants to occupy a broad range of habitats. It has been repeatedly suggested that rapid evolution of local adaptation to novel environments may enable invasive plants to occupy a broad range of habitats. However, the classical Darwinian view on evolution by natural selection is that the process is slow and gradual, occurring over thousands of years. Invasive plants typically have a relatively short residence time in their introduced ranges (decades or just a few centuries). Besides the time constraint, founder effects (reduction in population size and genetic diversity) may also limit the capacity of invasive plants to rapidly evolve local adaption. Thus, invasive plants may be less likely than native plants to evolve local adaptation. Interestingly, however, an expanding body of literature documents the existence of local adaptation in invasive plant species within their exotic ranges. Here, we did a phylogenetically controlled meta-analysis to compare invasive and native plant species for differences in the frequency and magnitude of local adaptation. The meta-analysis was based on different experiments performed in various habitats including grasslands, steppes, deserts, forests, mountains, wetlands and dunes, and used a total of 134 plant species in 52 families. Forty seven of these species (in 24 families) are alien invaders in the region where the studies were undertaken, while the other 91 species (in 38 families) are native. On average, local plants performed better than foreign plants, and invasive plant species expressed local adaptation just as frequently, and at least as strongly as that exhibited by native plant species. An analysis performed while taking into account different plant life-history traits showed that self-incompatible invasive plants exhibited significantly higher frequencies of local adaptation than native plants characterized by the same breeding system. Synthesis. The present results support the suggestion that rapid evolution of local adaptation may enable invasive plant species to occupy a broad range of novel habitats.

Invasive plant species subvert essential ecosystem services through a reduction in the abundance and genetic diversity of native plant species. A major challenge now facing land managers and policy makers is how to ensure persistence of native plants while limiting harmful impacts of invasions. Results from recent empirical studies suggest that native plants may evolve adaptations to invasive plants and that adaptive evolution in invasive plants could lessen the negative impacts of invasions. Here, we suggest ways in which knowledge of adaptive evolution in invasive and native plants could be utilized to more effectively manage invaded ecosystems.

Invasive plant species and climate change are among the biggest threats to the ecological integrity of many ecosystems, including those of protected areas. Effective management of invasive plants requires information regarding their spatial distributions. Using maximum entropy, we modeled habitat suitability for an invasive plant species Chromolaena odorata under current and future climatic conditions (HadGEM2‐ES and MIROC5) in protected areas of four West African countries (Benin, Côte d'Ivoire, Ghana, and Togo). Under current climatic conditions, approximately 73% of total land area within the protected areas was suitable for colonization by C. odorata . Under future climate projections, the total area of suitable habitats for this invasive plant was projected to decrease by 7–9% (HadGEM2‐ES) and 12–14% (MIROC5). Country‐specific patterns suggest that major protected areas in Côte d'Ivoire and Ghana will be more vulnerable to invasion by C. odorata than those in Benin and Togo under both current and future climatic scenarios. To maintain normal ecosystem functioning and provisioning of ecosystem services within the protected areas studied here, locations that have been identified as most vulnerable to invasion by C. odorata should be accorded proportionately higher priority when formulating appropriate management strategies.

Invasive alien plant species threaten native biodiversity, disrupt ecosystem functions and can cause large economic damage. Plant invasions have been predicted to further increase under ongoing global environmental change. Numerous case studies have compared the performance of invasive and native plant species in response to global environmental change components (i.e. changes in mean levels of precipitation, temperature, atmospheric CO2 concentration or nitrogen deposition). Individually, these studies usually involve low numbers of species and therefore the results cannot be generalized. Therefore, we performed a phylogenetically controlled meta-analysis to assess whether there is a general pattern of differences in invasive and native plant performance under each component of global environmental change. We compiled a database of studies that reported performance measures for 74 invasive alien plant species and 117 native plant species in response to one of the above-mentioned global environmental change components. We found that elevated temperature and CO2 enrichment increased the performance of invasive alien plants more strongly than was the case for native plants. Invasive alien plants tended to also have a slightly stronger positive response to increased N deposition and increased precipitation than native plants, but these differences were not significant (N deposition: P = 0.051; increased precipitation: P = 0.679). Invasive alien plants tended to have a slightly stronger negative response to decreased precipitation than native plants, although this difference was also not significant (P = 0.060). So while drought could potentially reduce plant invasion, increases in the four other components of global environmental change considered, particularly global warming and atmospheric CO2 enrichment, may further increase the spread of invasive plants in the future.

This study assessed the level of bark damage on baobab trees (Adansonia digitata) as caused by elephants (Loxodonta africana), and the possibility of finding refuges where baobab could escape bark damage within the Pendjari Biosphere Reserve (PBR). Distributions of elephants and baobab trees within the PBR were compared using presence records of both species taken along transect lines. Two sites (National Park vs. hunting zone) that differ in elephant density were compared for intensity of bark damage and correlations between the intensity of bark damage and stem size of the baobab trees and population structure of the baobab trees. Elephants and baobabs showed co-occurrence in PBR suggesting that there is nowhere to hide for baobabs. The intensity of bark damage was positively correlated with elephant density and baobab girth. Baobab population girth classes were not significantly different in areas with and without bark damage. Future studies should test whether there are certain baobab genotypes that can resist elephant damage. It could also be tested whether effective conservation of elephants in the PBR has resulted in a bull-biased population over its carrying capacity.

Glyphosate or N-(phosphonomethyl) glycine is a broad spectrum non-selective systemic herbicide, used to kill weeds, mainly in soybean crops. Nowadays there are many controversies about the intensive use of these herbicides due to the potential environmental impact and the effects on human health. The environmental impacts of commercial Glyphosate formulation Roundup were assessed by evaluation of acute and chronic toxicity of Danio rerio fish.The effects of glyphosate commercial formulations and glyphosate isopropylamine salt solutions were evaluated in different steps. First the lethal doses of Roundup herbicide toward the experimental models were determined. Subsequently the specie was exposed to sublethal concentrations of both, the commercial preparations and pure glyphosate salt in order to evaluate the chronic toxicity.Acute toxicity was assessed by calculating the mortality indexes and chronic toxicity by measuring several biochemical parameters such as the activity of marker enzymes like aspartate aminotransferase (AST), alanine aminotransferase (ALT) and acetylcholinesterase (AchE). The registers of histological alterations in liver tissue sections were also considered in this study.Commercial herbicides produce mortality of D. rerio and sublethal doses of these herbicides and the salt of the pure compound produce effects of chronic toxicity at the liver and muscle level; such are enough causes to limit the potential survival of these organisms in the medium. Fil: Jofré, Diego Martín. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Área Química General e Inorgánica; Argentina Fil: Alvarez, Maria de Fatima. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Área Química General e Inorgánica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Perez, E.. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia; Argentina Fil: Mohamed, F.. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia; Argentina Fil: Jeréz, María Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto Multidisciplinario de Investigaciones Biológicas de San Luis. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto Multidisciplinario de Investigaciones Biológicas de San Luis; Argentina Fil: Juri Ayub, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto Multidisciplinario de Investigaciones Biológicas de San Luis. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto Multidisciplinario de Investigaciones Biológicas de San Luis; Argentina Fil: Enriz, Ricardo Daniel. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Área Química General e Inorgánica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Giannini, Fernando Angel. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Área Química General e Inorgánica; Argentina

Summary •Rapid post-introduction evolution has been found in many invasive plant species, and includes changes in defence (resistance and tolerance) and competitive ability traits. Here, we explored the post-introduction evolution of a trade-off between resistance to and tolerance of herbivory, which has received little attention. •In a common garden experiment in a native range, nine invasive and 16 native populations of Brassica nigra were compared for growth and defence traits. •Invasive populations had higher resistance to, but lower tolerance of, herbivore damage than native populations. Invasive populations survived better and produced more seeds than native ones when released from herbivores; but fitness was equivalent between the regions under ambient herbivory. The invasive populations grew taller, and produced more biomass and lighter seeds than natives, irrespective of insecticide treatment. •In addition to supporting the idea of post-introduction rapid evolution of plant traits, our results also contribute to an emerging pattern of both increasing resistance and growth in invasive populations, contrary to the predictions of earlier theories of resistance–growth trade-offs.

Herbivores modify various ecological processes including interactions between native and exotic plants that may affect invasion success by the exotic plants. It is unknown whether different types of exotic herbivores have similar effects on native and exotic plants. Using two distinct data sets, we ran meta-analyses to compare exotic vertebrate and invertebrate herbivore preferences for, and effects on performance and population sizes of native and exotic plants. We found that exotic vertebrate herbivores have positive effects on exotic plant performance and population sizes, and no significant effects on native plants. Exotic invertebrates have significant negative effects on performance and population sizes of both exotic and native plants. Vertebrates prefer to feed on native plants relative to exotic plants, while invertebrates prefer the exotic plants to native plants. Thus the exotic vertebrate herbivores may aid invasiveness of exotic plants, in accordance with the invasional meltdown hypothesis, while exotic invertebrate herbivores probably have no net effect on invasion process of the exotic plants. Invertebrate herbivore preferences for exotic plants support the biotic resistance hypothesis, as the native plants probably resist the invertebrate herbivory. We also tested an evolutionary logic that posits that herbivores with similar evolutionary history as plants will affect the plants less negatively than plants with which they have not co-evolved. Our results indicate that there is no consistent pattern in effects of exotic vertebrate and invertebrate herbivores on exotic plants with or without which they have co-evolved.

1. Herbivore-induced plant volatiles (HIPVs) play an important role in host location of parasitoid wasps and may benefit the plant by top–down control of its herbivorous attackers. Although many studies have shown that accessions of plants differ in attractiveness to parasitoid wasps under controlled laboratory studies, few studies have confirmed that the most attractive accessions also sustain highest parasitism rates in the field. Here, we tested whether in-flight preference of parasitoids for HIPVs from cultivars of Brassica oleracea in the laboratory reliably predicts the parasitism rates of herbivores feeding on these cultivars in the field. 2. In wind tunnel tests in the laboratory, we ranked cultivars of B. oleracea for the preference of two congeneric parasitoids ( Cotesia glomerata and C. rubecula ) for their HIPVs. The cultivars were then compared for their relative parasitism rates of caterpillars in the field. Throughout the growth season in the field, we infested the different cultivars with Pieris caterpillars on a weekly basis. The caterpillars were recollected after 3 days, dissected and scored for the rate of parasitism. 3. Cultivars of B. oleracea that we identified as most attractive to parasitoids in the laboratory also sustained highest proportions of parasitism in the field. The composition of the headspace of the B. oleracea cultivars damaged by P. rapae differs among these cultivars in the amounts of terpenoids and methyl salicylate emitted, which may be responsible for the differential attraction of parasitoids to the cultivars. 4. Our results show that intraspecific variation in HIPVs of plants is paralleled by differential parasitism of caterpillars in the field. The widely used laboratory assays on HIPV-based preferences of parasitoids provided reliable information on relative parasitism differences of herbivores as found in the field. 5. Thereby, our work confirms that through HIPVs plants attract parasitoids that effectively parasitize herbivores even under the complex and variable abiotic and biotic conditions in (agro-) ecosystems.

Differences in plant and herbivore community assemblages between exotic andnative ranges may select for different levels of plant traits in invasive and native populations of plant species. Little is currently known of how herbivores may mediate competitive and facilitative interactions between invasive and native populations of plant species and their plant neighbors. Here, we conducted a common-garden field experiment to test whether invasive and native populations of Brassica nigra differ in phenotypic expressions of growth (biomass and plant height) and reproductive (seed yield) traits under different plant neighbor treatments and ambient vs. reduced level of insect herbivore damage on the B. nigra plants. We found significant interactive effects of plant neighbor treatments, level of insect herbivore damage on B. nigra plants, and invasive status of B. nigra on the phenotypic trait expressions.Plant neighbor treatments had minimal effects on phenotypic trait expressions by invasive populations of B. nigra under either level of insect herbivore damage. In contrast, for native populations of B. nigra, ambient level of insect herbivore damage resulted in plant neighbors facilitating expression of the traits above, while reduced damage resulted in plant neighbors competitively suppressing trait expression. Our results suggest that insect herbivores and plant neighbors interactively shape expression of plant traits in native and exotic ranges of invasive plants. Such interactions could potentially lead to different selection pressures on traits that determine antiherbivore defenses and plant–plant interactions.

Strong competition from invasive plant species often leads to declines in abundances and may, in certain cases, cause localized extinctions of native plant species. Nevertheless, studies have shown that certain populations of native plant species can co-exist with invasive plant species,suggesting the possibility of adaptive evolutionary responses of those populations to the invasive plants. Empirical inference of evolutionary responses of the native plant species to invasive plants has involved experiments comparing two conspecific groups of native plants for differences in expression of growth/reproductive traits: populations that have experienced competition from the invasive plant species (i.e. experienced natives) versus populations with no known history of interactions with the invasive plant species (i.e. naıve natives). Here, I employ a meta-analysis to obtain a general pattern of inferred evolutionary responses of native plant species from 53 such studies. In general, the experienced natives had significantly higher growth/reproductive performances than naıve natives, when grown with or without competition from invasive plants.While the current results indicate that certain populations of native plant species could potentially adapt evolutionarily to invasive plant species, the ecological and evolutionary mechanisms that probably underlie such evolutionary responses remain unexplored and should be the focus of future studies.

ACTH treatment in vivo enhances the activity of adrenal cytosol for supporting pregnenolone synthesis in adrenal mitochondria. Upon fractionation of adrenal cytosol by gel filtration through Sephadex G200, pregnenolone synthesis-stimulating activity is eluted just after 3H2O(Kd = 1.1--2.1). This late eluting steroidogenic activity is enhanced by ACTH treatment and diminished by cycloheximide treatment, which also inhibits adrenal protein synthesis and ACTH-induced steroidogenesis. Chromatography on Sephadex G-10 yields even further separation of steroidogenic factor(s) from inactive substances; it appears that the active factor(s) adsorbs to Sephadex and that such adsorption is enhanced by a greater degree of cross-linking in the gel. The phospholipids, cardiolipin, diphosphoinositide, and triphosphoinositide, are recovered partly in adrenal cytosol and, by virtue of their polyphosphorylated head group, specifically stimulate mitochondrial pregnenolone synthesis. It seems likely that the ACTH effect on cytosolic steroidogenic activity is due to changes in polyphosphoinositides, since these phospholipids are specifically stimulated by ACTH, cycloheximide blocks the ACTH-induced increase in polyphosphoinositides, and these phospholipids comigrate with steroidogenic activity during gel filtration of adrenal cytosol. These findings along with other findings from our laboratory suggest that polyphosphoinositides may function as a cycloheximide-sensitive mediator in the steroidogenic action of ACTH.

As with adrenocorticotropin pretreatment in vivo, addition of cardiolipin in vitro enhances adrenal mitochondrial pregnenolone synthesis and apparent binding of cholesterol to cytochrome P-450scc. These effects are relatively specific for glycerolipids containing two or more phosphate radicals in the polar head group, and changes in such phospholipids or comparably acting substances may play a role in mediating adrenocorticotropin- or other hormone-induced effects on membrane-associated enzymes.