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Anurag A. Agrawal - One of the best experts on this subject based on the ideXlab platform.
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growth defense tradeoffs for two major anti herbivore traits of the common milkweed Asclepias syriaca
Oikos, 2015Co-Authors: Tobias Züst, Sergio Rasmann, Anurag A. AgrawalAbstract:Costs of plant defense are a key assumption in evolutionary ecology, yet their detection has remained challenging. Here we introduce a novel method for quantifying plant growth using the common milkweed Asclepias syriaca and repeated non-destructive size measurements to experimentally test for costs of defensive traits. We estimated mechanistic components of plant growth (relative growth rate, net assimilation rate, specific leaf area and leaf-mass ratio) at two levels of fertilization (high and low), and related them to production of toxic cardenolides and exudation of sticky latex. We found negative genetic correlations between cardenolides and growth (most strongly with net assimilation rate) at both nutrient levels. Additionally, plants varied in their cardenolide response to low nutrients, and genetic families maintaining higher cardenolide production at low nutrient availability suffered proportionally larger reductions in growth. In contrast, the amount of latex was positively correlated with plant growth. Because latex is instantly deployed from a plant-wide system of pressurized laticifers, larger plants may simply exude proportionally more latex when damaged and thus plant size is likely to mask potential costs of latex synthesis. Unbiased quantification of mechanistic growth processes, coupled with the manipulation of nutrient or stress levels, is thus an effective approach to demonstrate allocation to defense and tradeoffs with growth, especially in long-lived plant species.
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Growth–defense tradeoffs for two major anti‐herbivore traits of the common milkweed Asclepias syriaca
Oikos, 2015Co-Authors: Tobias Züst, Sergio Rasmann, Anurag A. AgrawalAbstract:Costs of plant defense are a key assumption in evolutionary ecology, yet their detection has remained challenging. Here we introduce a novel method for quantifying plant growth using the common milkweed Asclepias syriaca and repeated non-destructive size measurements to experimentally test for costs of defensive traits. We estimated mechanistic components of plant growth (relative growth rate, net assimilation rate, specific leaf area and leaf-mass ratio) at two levels of fertilization (high and low), and related them to production of toxic cardenolides and exudation of sticky latex. We found negative genetic correlations between cardenolides and growth (most strongly with net assimilation rate) at both nutrient levels. Additionally, plants varied in their cardenolide response to low nutrients, and genetic families maintaining higher cardenolide production at low nutrient availability suffered proportionally larger reductions in growth. In contrast, the amount of latex was positively correlated with plant growth. Because latex is instantly deployed from a plant-wide system of pressurized laticifers, larger plants may simply exude proportionally more latex when damaged and thus plant size is likely to mask potential costs of latex synthesis. Unbiased quantification of mechanistic growth processes, coupled with the manipulation of nutrient or stress levels, is thus an effective approach to demonstrate allocation to defense and tradeoffs with growth, especially in long-lived plant species.
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Ant-aphid interactions on Asclepias syriaca are mediated by plant genotype and caterpillar damage
Oikos, 2012Co-Authors: Luis Abdala-roberts, Anurag A. Agrawal, Kailen A. MooneyAbstract:The means by which plant genotypes influence species interactions and arthropod community structure remain poorly understood. One potential, but largely unstudied mechanism is that occurring through plant genetic variation in induced responses to herbivory. Here we test whether induced responses to leaf damage and genotypic variation for induction in Asclepias syriaca influence interactions among Formica podzolica ants, the ant-tended aphid Aphis asclepiadis, and the untended aphid Myzocallis asclepiadis. In so doing, we assess genetic variation in plant-mediated interactions among different herbivore guilds. We conducted a three-way factorial field experiment manipulating plant genotype, leaf damage by specialist monarch caterpillars Danaus plexippus, and ant presence, and documented effects on aphid and ant abundances. Leaf damage increased Aphis abundance in both the presence and absence of ants and Myzocallis abundance under ant exclusion. In the presence of ants, leaf damage decreased Myzocallis abundance, likely due to effects on ant–Myzocallis interactions; ants showed a positive association with Myzocallis, leaf damage increased the strength of this association (425% more ants per aphid), and this in turn fed back to suppress Myzocallis abundance. Yet, these aggregate effects of leaf damage on Myzocallis and ants were underlain by substantial variation among milkweed genotypes, with leaf damage inducing lower aphid and ant abundances on some genotypes, but higher abundances on others. As a consequence, a substantial fraction of the variation in leaf damage effects on ants (R 2 0.42) was explained by milkweed genetic variation in the strength and sign of leaf damage effects on Myzocallis. Although plant genetic variation influenced Aphis abundance, this did not translate into genetic variation in ant abundance, and leaf damage did not influence Aphis–ant interactions. Overall, we show that variation in induced responses to herbivory is a relevant condition by which plant genotype influences interactions in plant-centered arthropod communities and provide novel results of effects on the third trophic level.
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specificity and trade offs in the induced plant defence of common milkweed Asclepias syriaca to two lepidopteran herbivores
Journal of Ecology, 2010Co-Authors: Robin A Bingham, Anurag A. AgrawalAbstract:Summary 1. We studied induced defences in common milkweed (Asclepias syriaca) to two specialist caterpillars (Danaus plexippus and Euchaetes egle) to test several hypotheses about co-evolution and defence allocation. 2. Latex, a potent defence of milkweed, showed nearly fivefold variation in the amount exuded among genetic families and more than doubled production in response to herbivory by D. plexippus; this induced latex response was fourfold stronger than the latex response to E. egle herbivory. In contrast, D. plexippus and E. egle equivalently induced foliar cardenolide concentration (an average increase of 26%). 3. We found broad-sense heritable variation for the induced plant responses, and there was a genetic correlation between the responses induced by the two herbivores for cardenolides, but not for latex. We found no genetic correlation between investment in latex and cardenolides in any of the treatments. 4. Using a bias-corrected Monte Carlo procedure, we found strong evidence for a trade-off between constitutive and induced cardenolides, but not for latex. 5. Synthesis. As natural selection by specific herbivores varies in space and time, we expect that these defence traits in A. syriaca will evolve independently, with the expression of cardenolides showing less specificity, as well as being constrained by a trade-off between constitutive and induced defence.
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Specificity and trade‐offs in the induced plant defence of common milkweed Asclepias syriaca to two lepidopteran herbivores
Journal of Ecology, 2010Co-Authors: Robin A Bingham, Anurag A. AgrawalAbstract:Summary 1. We studied induced defences in common milkweed (Asclepias syriaca) to two specialist caterpillars (Danaus plexippus and Euchaetes egle) to test several hypotheses about co-evolution and defence allocation. 2. Latex, a potent defence of milkweed, showed nearly fivefold variation in the amount exuded among genetic families and more than doubled production in response to herbivory by D. plexippus; this induced latex response was fourfold stronger than the latex response to E. egle herbivory. In contrast, D. plexippus and E. egle equivalently induced foliar cardenolide concentration (an average increase of 26%). 3. We found broad-sense heritable variation for the induced plant responses, and there was a genetic correlation between the responses induced by the two herbivores for cardenolides, but not for latex. We found no genetic correlation between investment in latex and cardenolides in any of the treatments. 4. Using a bias-corrected Monte Carlo procedure, we found strong evidence for a trade-off between constitutive and induced cardenolides, but not for latex. 5. Synthesis. As natural selection by specific herbivores varies in space and time, we expect that these defence traits in A. syriaca will evolve independently, with the expression of cardenolides showing less specificity, as well as being constrained by a trade-off between constitutive and induced defence.
Aaron F Howard - One of the best experts on this subject based on the ideXlab platform.
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Asclepias syriaca (Common Milkweed) flowering date shift in response to climate change.
Scientific reports, 2018Co-Authors: Aaron F HowardAbstract:The consequences of altered flowering dates due to climate change can be severe, especially for plants that rely on coordinated flower and pollinator emergence for reproduction. The plant Asclepias syriaca (Common Milkweed) relies on pollinators for movement of its pollen and evidence suggests that it has recently been declining. Given these factors and this plant’s importance as a host species for the declining Danaus plexippus (Monarch Butterfly), it is critical to determine if its flowering is being modified by climate change. As a first step to answering this question I quantified the relationship between climate and flowering date for A. syriaca using data from the USA National Phenology Network repository and the National Oceanic and Atmospheric Administration. I found that temperatures were higher than they had been historically (1895–2010) and mean flowering dates occurred earlier with higher temperatures. Additionally, there is a significant negative interactive effect of temperature and year on flowering date indicating that from 2011 through 2016 higher temperatures are correlated with increasingly earlier flowering dates. The change in flowering appears to be symmetrical in regards to the flowering time distribution, in that along with the mean, both maximum and minimum flowering dates are occurring earlier, as well. There is no evidence that earlier flowering is due to earlier initial growth or results in later fruit ripening. Consequences of this shift in flowering can only be speculated upon at this point, but due to the ecological importance of A. syriaca and its susceptibility to phenological mismatch, they should be considered when developing conservation plans for A. syriaca and the organisms for which it is a host.
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Self-pollination rate and floral-display size in Asclepias syriaca(Common Milkweed) with regard to floral-visitor taxa
BMC evolutionary biology, 2014Co-Authors: Aaron F Howard, Edward M. BarrowsAbstract:Background Animals fertilize thousands of angiosperm species whose floral-display sizes can significantly influence pollinator behavior and plant reproductive success. Many studies have measured the interactions among pollinator behavior, floral-display size, and plant reproductive success, but few studies have been able to separate the effects of pollinator behavior and post-pollination processes on angiosperm sexual reproduction. In this study, we utilized the highly self-incompatible pollinium-pollination system of Asclepias syriaca (Common Milkweed) to quantify how insect visitors influenced male reproductive success measured as pollen removal, female reproductive success measured as pollen deposition, and self-pollination rate. We also determined how floral-display size impacts both visitor behavior and self-pollination rate.
John J. Couture - One of the best experts on this subject based on the ideXlab platform.
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Intraspecific competition reduces plant size and quality and damage severity increases defense responses in the herbaceous perennial, Asclepias syriaca
Plant Ecology, 2020Co-Authors: Abigail A. R. Kula, John J. Couture, Philip A. Townsend, Harmony J. DalgleishAbstract:Competition among plants within populations affects plant size, nutrient status and allocation to defenses. Herbivory places additional stress on plant allocation of resources. When resources are limited due to intraspecific competition, induced defenses may reduce costs of defense responses and trade-offs between allocation to growth or defense. We hypothesized that increased intraspecific competition would result in a decrease in plant size and leaf tissue nutrient quality, and that both intraspecific competition and leaf damage severity would affect inducibility of leaf defensive traits. We tested these hypotheses in common milkweed ( Asclepias syriaca ) using greenhouse experiments that manipulated plant density and damage severity treatments. We measured a suite of leaf traits generally related with herbivore performance, including size; nitrogen, carbon, lignin, and fiber concentrations; and latex production. Increased density decreased plant size and leaf nutrient quality, but increased lignin levels. Damage severity increased leaf lignin levels and latex production. There were no density–damage severity interactions. We additionally addressed the question of whether plants respond differently to simulated or natural herbivory and hypothesized that insect herbivores and mechanical plant tissue removal would similarly affect induced defensive responses. Leaf fiber and lignin increased in response to damage, but the response was greater on plants subjected to simulated, compared with caterpillar herbivory. Other plant traits responded similarly to either damage type. Our findings suggest that intraspecific competition has the potential to generate feedbacks among plants and herbivores as plants respond to herbivory.
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Fine-scale spatial structuring of genotypes and phenotypes in natural populations of Asclepias syriaca
Perspectives in Plant Ecology Evolution and Systematics, 2020Co-Authors: Angela Ricono, John J. Couture, Nichole W. Gustafson, Erin Eichenberger, Katherine Stahl, Hannah Call, Joshua R. Puzey, Harmony J. DalgleishAbstract:Abstract The majority of plants have the ability to reproduce asexually. Despite the importance of asexual reproduction, we still have a limited understanding of how clonality impacts phenotypic and genetic variation within natural populations. Here, we collected phenotypic and genetic data on spatially mapped ramets of common milkweed (Asclepias syriaca) from 10 belt transects from three populations to determine the average size and extent of milkweed clones, whether genotypes and phenotypes were spatially clustered, and whether ramets from the same clone were more similar to each other phenotypically than ramets from different clones. Only 14 % of the 141 ramets that were genotyped belonged to the same clone as another genotyped ramet. Although ramets from the same clone were, on average, closer together than ramets from different clones, we found that the minimum distance between ramets from the same clone was significantly larger than the minimum distance observed between non-clone ramets. Ramets within half a meter of each other had less than a 7% probability of being the same genotype. The high degree of unique genotypes within a single belt transect indicates that sexual reproduction is much more common in milkweed populations than previously thought. Ramets from the same clone were not more similar to each other in height, reproductive allocation, herbivory severity, or leaf traits than ramets from different clones. Our data support the conclusion that even small patches of milkweed that are phenotypically similar are unlikely to be a single clone.
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elevated temperature and periodic water stress alter growth and quality of common milkweed Asclepias syriaca and monarch danaus plexippus larval performance
Arthropod-plant Interactions, 2015Co-Authors: John J. Couture, Shawn P Serbin, Philip A. TownsendAbstract:In this study, we examined the independent and interactive effects of temperature and water availability on the growth and foliar traits of common milkweed (Asclepias syriaca) and performance of a specialist herbivore, larvae of the monarch butterfly (Danaus plexippus). Milkweed from multiple population sources collected across a latitudinal gradient in Wisconsin, USA, were grown under all combinations of ambient or elevated temperature and the presence or absence of periodic water stress. Elevated temperature marginally increased, while water stress decreased plant growth. Milkweed from more northerly latitudes experienced larger growth responses to elevated temperature and were more resistant to water stress, especially under higher temperatures. Elevated temperature and water stress also altered milkweed composite foliar trait profiles. Elevated temperature generally increased leaf nitrogen and structural compounds, and decreased leaf mass per area. Water stress also elevated foliar nitrogen, but reduced defensive traits. Monarch larvae performed well on milkweed under elevated temperature and water stress, but gained the most mass on plants exposed to both treatments in combination. Our findings suggest that milkweed populations from more northerly latitudes in the upper Midwest may benefit more from rising temperatures than those in southerly locations, but that these beneficial effects depend on water availability. Monarch larvae grew larger on plants from all experimental treatments relative to ambient condition controls, indicating that future changes in milkweed presence on the landscape will likely influence monarch populations more than the effects of future changes in plant quality on larval performance.
Katalin Török - One of the best experts on this subject based on the ideXlab platform.
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invasive Asclepias syriaca can have facilitative effects on native grass establishment in a water stressed ecosystem
Applied Vegetation Science, 2018Co-Authors: Katalin Szitár, Gyorgy Kroeldulay, Katalin TörökAbstract:QUESTION: What is the effect of invasive common milkweed (Asclepias syriaca L.) on the germination and early establishment of native grass species during open sand grassland vegetation recovery in old‐fields? LOCATION: Fulophaza Sand Dune Area, Hungary. METHODS: A small‐scale experiment was carried out in a sandy old‐field infested with Asclepias. We designated 36 2 m × 2 m plots in patches of Asclepias. We seeded two native grass species Festuca vaginata and Stipa borysthenica in 12 plots each (a third of the plots was left unseeded). We applied repeated mechanical removal of Asclepias shoots on half of the plots for two growing seasons. The number and above‐ground cover of the two grass seedlings were evaluated for two growing seasons. RESULTS: The number and above‐ground cover of Festuca and Stipa seedlings did not increase after applying Asclepias shoot removal during the 2 years of the study. We found lower seedling number and cover of Festuca in plots with Asclepias shoot removal in the second year, when a severe summer drought occurred at the study site. The number and cover of the Stipa seedlings did not differ between plots with Asclepias shoot removal and control plots throughout the experiment. CONCLUSIONS: We did not find any negative effects of the presence of the invasive Asclepias during open sand grassland regeneration in terms of germination and early establishment of the dominant grass species. We even detected a nurse effect of Asclepias on Festuca, where the shade of Asclepias may have mitigated the unfavourable abiotic conditions for Festuca caused by summer drought. This mitigation was not observed in the case of Stipa, which can better tolerate summer droughts. Our results suggest that Asclepias control is not required for a successful open sand grassland restoration in the early phase of vegetation recovery, and restoration efforts should focus on the mitigation of propagule limitation of native grasses. However, further information is needed about the effects of Asclepias on other elements of the biota and in later phases of secondary succession.
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Invasive Asclepias syriaca can have facilitative effects on native grass establishment in a water‐stressed ecosystem
Applied Vegetation Science, 2018Co-Authors: Katalin Szitár, György Kröel-dulay, Katalin TörökAbstract:QUESTION: What is the effect of invasive common milkweed (Asclepias syriaca L.) on the germination and early establishment of native grass species during open sand grassland vegetation recovery in old‐fields? LOCATION: Fulophaza Sand Dune Area, Hungary. METHODS: A small‐scale experiment was carried out in a sandy old‐field infested with Asclepias. We designated 36 2 m × 2 m plots in patches of Asclepias. We seeded two native grass species Festuca vaginata and Stipa borysthenica in 12 plots each (a third of the plots was left unseeded). We applied repeated mechanical removal of Asclepias shoots on half of the plots for two growing seasons. The number and above‐ground cover of the two grass seedlings were evaluated for two growing seasons. RESULTS: The number and above‐ground cover of Festuca and Stipa seedlings did not increase after applying Asclepias shoot removal during the 2 years of the study. We found lower seedling number and cover of Festuca in plots with Asclepias shoot removal in the second year, when a severe summer drought occurred at the study site. The number and cover of the Stipa seedlings did not differ between plots with Asclepias shoot removal and control plots throughout the experiment. CONCLUSIONS: We did not find any negative effects of the presence of the invasive Asclepias during open sand grassland regeneration in terms of germination and early establishment of the dominant grass species. We even detected a nurse effect of Asclepias on Festuca, where the shade of Asclepias may have mitigated the unfavourable abiotic conditions for Festuca caused by summer drought. This mitigation was not observed in the case of Stipa, which can better tolerate summer droughts. Our results suggest that Asclepias control is not required for a successful open sand grassland restoration in the early phase of vegetation recovery, and restoration efforts should focus on the mitigation of propagule limitation of native grasses. However, further information is needed about the effects of Asclepias on other elements of the biota and in later phases of secondary succession.
Edward M. Barrows - One of the best experts on this subject based on the ideXlab platform.
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Self-pollination rate and floral-display size in Asclepias syriaca(Common Milkweed) with regard to floral-visitor taxa
BMC evolutionary biology, 2014Co-Authors: Aaron F Howard, Edward M. BarrowsAbstract:Background Animals fertilize thousands of angiosperm species whose floral-display sizes can significantly influence pollinator behavior and plant reproductive success. Many studies have measured the interactions among pollinator behavior, floral-display size, and plant reproductive success, but few studies have been able to separate the effects of pollinator behavior and post-pollination processes on angiosperm sexual reproduction. In this study, we utilized the highly self-incompatible pollinium-pollination system of Asclepias syriaca (Common Milkweed) to quantify how insect visitors influenced male reproductive success measured as pollen removal, female reproductive success measured as pollen deposition, and self-pollination rate. We also determined how floral-display size impacts both visitor behavior and self-pollination rate.
