Premise Human activity has significantly altered the salt cycle, affecting an estimated 2.5 billion acres of soil worldwide. Elevated soil salinity is a well-known plant stressor, but it may also affect interactions between plants and insects, which are often sodium limited. Elevated sodium in nectar can increase pollinator visitation, but no previous study has examined the effects of elevated soil salinity on visitation by pollen-collecting bees.Methods Our study tested whether increased soil salinity impacts pollen sodium and Bombus spp. visitation to Solanum carolinense, a buzz-pollinated perennial wildflower that rewards pollinators only with pollen. Soil salinity around the root zone of Solanum carolinense growing wild in an early successional field was artificially increased with a salt solution to observe changes in pollen sodium and other cations, pollen viability, and pollinator visitation.Results Salt addition to the soil increased soil salinity by over five-fold, but there was no effect on the sodium levels of S. carolinense pollen. The salt treatment had no effect on pollinator visitation or pollen viability.Conclusions Although high soil salinity has been shown to increase nectar sodium levels and thus pollinator visitation, we infer from our results that S. carolinense is able to largely exclude sodium from its pollen, preventing high salinity soil from affecting pollinator attraction and pollen viability.

The nest-founding stage represents an especially vulnerable period of the bumble bee (Bombus) life cycle, during which solitary queens must locate and collect sufficient foraging resources to sustain themselves and their brood. Yet, we lack contemporary information about floral foraging resources used by queens in early spring. Here, we use next-generation sequencing to characterize the floral species used by queens for pollen provisions during early nest establishment. We collected pollen loads from over 100 wild bumble bee queens at working farms, rural and city parks, and nature preserves across the Piedmont region of Virginia, USA. Using metabarcoding of two universal DNA barcodes for plants, ITS2 and rbcL, we determined the taxonomic composition of pollen used by queens. Pollen loads contained native and non-native woody (e.g., Cercis: Fabaceae, Prunus: Rosaceae, Salix: Salicaceae), herbaceous (e.g., Lamium: Lamiaceae, Viola: Violaceae), and vine (e.g., Lonicera: Caprifoliaceae) taxa. The non-native Lamium and Elaeagnus (Elaeagnaceae) most frequently hosted foraging queens, owing in part to their abundance across sites and the season. Pollen composition varied more over time than among bumble bee species or across sites, but land cover predicted a small amount of variation in pollen composition. Specifically, the percentage of crop land within 1 km increased the representation of Lamium in queen pollen loads, likely reflecting the abundance of the disturbance-adapted flower in fallow cornfields. Finally, the pollen communities detected by rbcL were twice as diverse as those by ITS2, perhaps owing to the better taxonomic resolution afforded by the fast-evolving rbcL marker. This study demonstrates that queens are flexible foragers and that among the most common Bombus species, plant phenology drives pollen use more than species identity. Further, this study highlights the importance of monitoring pollen diets to inform regional management strategies and considerations about metabarcoding techniques.

The management of roadside habitat may be an important component of the conservation of declining pollinators, but insect mortality along roadsides can be high, creating a potential “ecological trap.” Runoff from winter applications of deicing salt can increase soil salinity along roadsides, and if this results in higher sodium levels in floral nectar, it could increase the attractiveness of roadside plants to pollinators, possibly accentuating the ecological trap effect. We compared the soil salinity in a highway median to soil collected from nearby fields and compared the Na + concentrations in nectar from common milkweed ( Asclepias syriaca ) from these two habitats. We also manipulated soil salinity in field populations of A. syriaca by adding brine solution to document changes in nectar Na + and pollinator visitation. We found that soil salinity in the median of a highway in Clarke County, VA was 2.3 times higher than the salinity of field soil, however nectar from A. syriaca in the two habitats did not differ significantly in Na + concentration. Addition of brine to field soil increased soil salinity 17-fold and significantly increased the level of Na + in A. syriaca nectar. Pollinators visited A. syriaca umbels that received the brine treatment twice as frequently as controls. Implications for insect conservation: We conclude that elevated soil salinity is capable of increasing nectar Na + and the attractiveness of A. syriaca flowers to insect pollinators, but roadside soil salinity in our study was not high enough to enhance an ecological trap effect of roadside vegetation.

This study investigates the feasibility of 3D printing soil structures that could support plant life. Stand-alone soil structures were successfully printed without additives using an extrusion method. When the water content is properly controlled, the printed structures are able to support germination and growth of plants. Additionally, we show that the water retention capabilities of printed structures differ from potted soil of the same composition. In three different soil textures, we correlate the drying characteristics with the ability of the soil to support plant growth, and show a fundamental difference in the soil-water characteristics of the extruded soils.

Brown-headed cowbirds (Molothrus ater) are generalist obligate brood parasites, laying in the nest of nearly 300 avian species, and successfully parasitizing well over 100 host species. Cowbird eggs are generally considered non-mimetic, although some have suggested that cowbird eggs resemble several of their host species' eggs. To date, no investigation has examined the level of avian-perceived similarity between cowbird and diverse host eggs in the contexts of light characteristics at the nest and the visual system of the relevant viewer. Because the cowbird exploits a wide range of species that lay in a variety of nest types, hosts view these eggs under an array of light conditions which could facilitate or hinder egg discrimination. When considering the visual system of the relevant viewers and the light conditions at their nest, we found that the coloration of cowbird eggs was more similar to host than non-host species' eggs. Host responses (whether they accept or reject cowbird eggs) were not statistically different when hosts perceived a large chromatic difference between their own eggs and the cowbird's eggs. Instead, we found that host responses were predicted by the degree to which nesting light conditions facilitated color similarity between host and cowbird eggs, such that hosts typically nesting under light conditions where this color discrimination task was more challenging were more likely to reject cowbird eggs. This suggests that the nesting light environment may have selected for increased coevolved egg recognition abilities in a suite of cowbird host species, even in the absence of parasitic egg color mimicry.

Insect pollinators readily learn olfactory cues, and this is expected to select for ‘honest signals' that provide reliable information about floral rewards. However, plants might alternatively produce signals that exploit pollinators' sensory biases, thereby relaxing selection for signal honesty. We examined the innate and learned preferences of Bombus impatiens for Mimulus guttatus floral scent phenotypes corresponding to different levels of pollen rewards in the presence and absence of the innately attractive floral volatile compound β-trans-bergamotene. Bees learned to prefer honest signals after foraging on live M. guttatus flowers, but only exhibited this preference when presented floral scent phenotypes that did not include β-trans-bergamotene. Our results suggest that a sensory bias for β-trans-bergamotene overrides the ability of B. impatiens to use honest signals when foraging on M. guttatus . This may represent a deceptive pollination strategy that allows plants to minimize investment in costly rewards without incurring reduced rates of pollinator visitation.

A potential driver of pollinator declines that has been hypothesized but seldom documented is the introduction of exotic pollinator species. International trade often involves movement of many insect pollinators, especially bees, beyond their natural range. For agricultural purposes or by inadvertent cargo shipment, bee species successfully establishing in new ranges could compete with native bees for food and nesting resources. In the Mid-Atlantic United States, two Asian species of mason bee (Osmia taurus and O. cornifrons) have become recently established. Using pan-trap records from the Mid-Atlantic US, we examined catch abundance of two exotic and six native Osmia species over the span of fifteen years (2003–2017) to estimate abundance changes. All native species showed substantial annual declines, resulting in cumulative catch losses ranging 76–91% since 2003. Exotic species fared much better, with O. cornifrons stable and O. taurus increasing by 800% since 2003. We characterize the areas of niche overlap that may lead to competition between native and exotic species of Osmia, and we discuss how disease spillover and enemy release in this system may result in the patterns we document.

Approximately 90% of all annual net primary productivity in temperate deciduous forests ends up entering the detritus food web as leaf litter. Due to chemical and physical differences from native litter, inputs from invasive species may impact the litter-dwelling community and ecosystem processes. We compared leaf-litter nutritional quality and decomposition rates from two invasive shrubs, Lonicera maackii and Rhamnus davurica, and the invasive tree Ailanthus altissima to litter from native oak-hickory forest in the Shenandoah Valley of Virginia, USA. We sampled litter from both invaded and uninvaded habitats and conducted litter colonization experiments to test for effects on microflora and the litter-dwelling arthropod communities. Litter from all three invasive species decomposed more rapidly than native litter, with native habitats averaging two to nearly five times as much litter by June. Invasive litter had higher nitrogen concentration and lower C:N ratios than native litter. Invasive litter supported greater growth of bacteria and fungi. Higher numbers of arthropods colonized invasive litter than native litter, but litter arthropod numbers on the forest floor of invaded habitats dropped in the early summer as litter decomposed. Litter had no effect on arthropod richness. Over short time scales, our results indicate that these invasive species represent beneficial, novel resources for the litter-dwelling community. However, the short-lived nature of this resource resulted in a crash in the abundance of the litter-dwelling organisms once the litter decomposed. As a whole, native habitat seems to support a larger, more stable litter-dwelling community over the course of a growing season.

Artificial light at night (ALAN) has been shown to alter aspects of plant growth, but we are not aware of any studies that have examined whether the effects of ALAN on plants depend upon the backdrop of variation in other abiotic factors that plants encounter in field populations. We conducted a field experiment to investigate whether ALAN affects the growth and anti-herbivore defenses of common milkweed, Asclepias syriaca, and whether the effects of ALAN are influenced by plant density or soil moisture content. Artificial light at night, soil moisture, and plant density were manipulated according to a split-plot factorial design. Although increasing soil moisture by watering had no significant effects on latex exudation, attributes of plant growth generally responded positively to watering. The basal stem diameter (BSD) and height of plants were affected by ALAN × soil moisture interactions. For both of these variables, the positive effects of ALAN were greater for plants that were not watered than for plants that were. Basal stem diameter was also affected by an ALAN × plant density interaction, and the positive effect of ALAN on BSD was greater in the low-density treatment than in the high-density treatment. Our results demonstrate that the effects of ALAN on plant growth can be altered by soil moisture and plant density. Consequently, the effects of ALAN on plants in nature may not be consistent with existing frameworks that do not account for critical abiotic variables such as water availability or biotic interactions between plants such as competition.

27 1) Floral odors play an important role in attracting insect pollinators. Because pollinators 28 visit flowers to obtain pollen and nectar rewards, they should prefer floral odor profiles 29 associated with the highest-rewarding flowers (honest signals). In previous work, bumble 30 bees exhibited a preference for flowers from outbred over inbred Mimulus guttatus 31 plants. Pollen is the only floral reward in M. guttatus , and pollen viability (a reliable 32 indicator of protein content) is reduced in inbred plants. Yet, differences in pollen 33 viability did not explain the observed preferences. 34 2) In this study we examined the floral volatile profiles of inbred and outbred M. guttatus to 35 identify inbreeding effects and associations between volatile compounds and the number 36 of viable pollen grains per flower, designated ‘PRQ’ (pollen reward quality). We also 37 conducted pairwise choice tests with Bombus impatiens to evaluate the ability of bees to 38 discriminate between odors of rewarding and nonrewarding flowers and to determine 39 whether bumble bee preferences are explained by differences in the floral odors of inbred 40 and outbred plants. 41 42 43 44 45 46 47 48 these the of the male-fertile bees foraged a two-week period on a greenhouse population guttatus plants that included inbred and outbred plants with quantity and viability, including male-sterile plants. We matched plants in a given pairwise test for equal numbers of open flowers. choices of 40 for pairwise test. 'alarm calls' from increase to and their enemies in

Abstract Plants with crassulacean acid metabolism (CAM) are increasing in distribution and abundance in drylands worldwide, but the underlying drivers remain unknown. We investigate the impacts of extreme drought and CO2 enrichment on the competitive relationships between seedlings of Cylindropuntia imbricata (CAM species) and Bouteloua eriopoda (C4 grass), which coexist in semiarid ecosystems across the Southwestern United States. Our experiments under altered water and CO2 water conditions show that C. imbricata positively responded to CO2 enrichment under extreme drought conditions, while B. eriopoda declined from drought stress and did not recover after the drought ended. Conversely, in well‐watered conditions B. eriopoda had a strong competitive advantage on C. imbricata such that the photosynthetic rate and biomass (per individual) of C. imbricata grown with B. eriopoda were lower relative to when growing alone. A meta‐analysis examining multiple plant families across global drylands shows a positive response of CAM photosynthesis and productivity to CO2 enrichment. Collectively, our results suggest that under drought and elevated CO2 concentrations, projected with climate change, the competitive advantage of plant functional groups may shift and the dominance of CAM plants may increase in semiarid ecosystems.

We investigated the response of a model facultative CAM plant (Mesembryanthemum crystallinum) and its competition with a C3 grass (Bromus mollis) to changes in rainfall regime. Seedlings of M. crystallinum and B. mollis in both monoculture and mixtures growing in shallow and deep pots were subjected to three levels of intra-seasonal rainfall variability and rainfall seasonality in both high water and low water conditions. Response of plants were evaluated by nocturnal carboxylation and biomass. A high rate of water drainage beneath root zones in coarse soil led to a negative response of M. crystallinum and B. mollis in monoculture under increased intra-seasonal rainfall variability. Seasonal rainfall shifts to later dates during the growing season generally favored the growth of M. crystallinum and B. mollis in monoculture, with the exception of high water stress conditions whereby drought-intolerant species B. mollis was disfavored. Rainfall seasonality but not intra-seasonal rainfall variability affected nocturnal carboxylation by M. crystallinum in monoculture. We suggest that soil texture, root depth, and rainfall gradient are important mediators of plant growth under increased intra-seasonal rainfall variability. Drought severity and the ability of a plant to tolerate drought and can greatly affect its response to the seasonal timing of rainfall. Nocturnal carboxylation by M. crystallinum in response to rainfall variability depends on the timescale.

The goal of this study was to discover the nature and intensity of the interaction between an exotic invader Ailanthus altissima (Mill.) Swingle and its coexisting native Robinia pseudoacacia L. and consider management implications. The study occurred in the Mid-Appalachian region of the eastern United States. Ailanthus altissima can have a strong negative influence on community diversity and succession due to its allelopathic nature while R. pseudoacacia can have a positive effect on community diversity and succession because of its ability to fix nitrogen. How these trees interact and the influence of the interaction on succession will have important implications for forests in many regions of the world. An additive-replacement series common garden experiment was established to identify the type and extent of interactions between these trees over a three-year period. Both A. altissima and R. pseudoacacia grown in monoculture were inhibited by intraspecific competition. In the first year, A. altissima grown with R. pseudoacacia tended to be larger than A. altissima in monoculture, suggesting that R. pseudoacacia may facilitate the growth of A. altissima at the seedling stage. After the second year, R. pseudoacacia growth decreased as the proportion of coexisting A. altissima increased, indicating inhibition of R. pseudoacacia by A. altissima even though the R. pseudoacacia plants were much larger aboveground than the A. altissima plants. In early successional sites A. altissima should be removed, particularly in the presence of R. pseudoacacia in order to promote long-term community succession.

Inbreeding in plants is well known to affect plant-herbivore interactions, but these effects can depend on herbivore host breadth. If the phenotypic effects of inbreeding are analogous to those of environmental stress, the plant stress hypothesis predicts that generalist herbivores will perform better on inbred relative to outbred plants because inbreeding is expected to lower chemical defenses. The plant vigor hypothesis predicts that specialist herbivores will perform better on outbred relative to inbred plants because specialists are more tolerant of plant defenses and benefit from the higher nutritional quality of outbred plants. However, these plant defense theories do not account for structural defenses. Using a factorial design, we examined effects of inbreeding and trichome density in Mimulus guttatus on performance of the generalist, Helicoverpa zea, and the specialist, Junonia coenia. We also examined preferences of each herbivore for leaf disks and olfactory cues from inbred vs. outbred plants. The generalist H. zea developed most efficiently on inbred plants. The specialist J. coenia exhibited the greatest mass gain and pupal mass and developed fastest on outbred plants. Trichomes negatively affected performance of both species. Helicoverpa zea did not exhibit strong preferences for inbred vs. outbred plants, but J. coenia consistently preferred outbred plants. Our results support predictions on the effects of inbreeding on herbivore performance, but trichomes reduced performance of both herbivores. We conclude that the ability of the plant stress and plant vigor hypotheses to predict inbreeding effects on plant-herbivore interactions may depend on which plant traits are affected by inbreeding.

SummaryInvasive plants can seriously threaten biodiversity and ecosystem function. Thus, controlling the abundance and mitigating the deleterious effects of invasive plants is imperative. The effectiveness of removal methods could vary based on potential damage to non‐target species and on the ecological context of invasion. For example, species‐poor communities might benefit disproportionately from invasive removal because they tend to be more heavily invaded than species‐rich communities. In this study, we tested the efficacy of two common methods of invasive plant control, hand removal and 2,4‐D herbicide application, against the invasive forb, Galium verum. We further tested whether the community response to G. verum removal varied across communities that differed in native grass richness (one, three or six species) and composition. Grass diversity did not interact with G. verum removal to influence any response. Instead, hand removal and herbicide application each reduced G. verum stem density by >50% relative to controls. Furthermore, hand removal of G. verum increased species richness by 25% relative to controls and herbicide‐sprayed plots. Despite this benefit, hand removal is labour‐intensive and impractical for large areas. These results also suggest that applying herbicide may control G. verum spread without substantially reducing forb diversity in invaded tallgrass prairie. Thus, herbicide application may be most suitable for grasslands with low native forb diversity, especially in managed grasslands and pastures where maintaining native forb diversity is a lower priority than maintaining high grass productivity.

AbstractAbstract Plants with crassulacean acid metabolism (CAM) are increasing their abundance in drylands worldwide. The drivers and mechanisms underlying the increased dominance of CAM plants and CAM expression (i.e., nocturnal carboxylation) in facultative CAM plants, however, remain poorly understood. We investigated how nutrient and water availability affected competition between Mesembryanthemum crystallinum (a model facultative CAM species) and the invasive C3 grass Bromus mollis that co‐occur in California's coastal grasslands. Specifically we investigated the extent to which water stress, nutrients, and competition affect nocturnal carboxylation in M. crystallinum. High nutrient and low water conditions favored M. crystallinum over B. mollis, in contrast to high water conditions. While low water conditions induced nocturnal carboxylation in 9‐week‐old individuals of M. crystallinum, in these low water treatments, a 66% reduction in nutrient applied over the entire experiment did not further enhance nocturnal carboxylation. In high water conditions M. crystallinum both alone and in association with B. mollis did not perform nocturnal carboxylation, regardless of the nutrient levels. Thus, nocturnal carboxylation in M. crystallinum was restricted by strong competition with B. mollis in high water conditions. This study provides empirical evidence of the competitive advantage of facultative CAM plants over grasses in drought conditions and of the restricted ability of M. crystallinum to use their photosynthetic plasticity (i.e., ability to switch to CAM behavior) to compete with grasses in well‐watered conditions. We suggest that a high drought tolerance could explain the increased dominance of facultative CAM plants in a future environment with increased drought and nitrogen deposition, while the potential of facultative CAM plants such as M. crystallinum to expand to wet environments is expected to be limited.

Exotic plants are often most successful in high resource environments. By drawing down available resources, species-rich communities may be able to reduce exotic success when resource supply is elevated. We tested the prediction that exotic success would be greatest in species-poor communities when nitrogen availability is high. We also tested two underlying assumptions of this prediction: species-rich communities draw down soil nitrogen availability more than species-poor communities following fertilization and exotic success increases when soil nitrogen availability is high. In a restored grassland where native grass diversity was manipulated (one, three, or five-species) seven years earlier to form a gradient in species richness, we manipulated nitrogen availability directly via fertilization, and indirectly via burning. We then examined the success of the exotic forb Galium verum L. Contrary to our prediction, diversity and nutrient treatments did not jointly influence exotic success. Instead, one-time fertilization increased exotic biomass in the first year of the study. This likely occurred because the effect of nutrient treatments on nitrogen availability was independent of diversity treatment. Thus, we found no evidence that species-rich communities are better able to reduce exotic biomass when nitrogen is added than are species-poor communities. This suggests that in some systems, the effects of increasing species richness can be overwhelmed by the effects of nutrient addition that promote exotic success.

Nutrient pulses can facilitate species establishment and spread in new habitats, particularly when one species more effectively uses that nutrient pulse. Biological differences in nutrient acquisition between native and exotic species may facilitate invasions into a variety of habitats including deciduous forest understories. Alliaria petiolata (Bieb.) Cavara & Grande is an important invader of deciduous forest understories throughout much of North America. These understory communities contain many species which perform the majority of their growth and reproduction before canopy closure in spring. Because A. petiolata is a wintergreen biennial that can be active during autumn and winter, it may utilize nutrients released from decaying leaf litter before its competitors. To investigate this we manipulated the timing of leaf litter addition (fall or spring) and experimentally simulated the nutrient pulse from decaying leaves using artificial fertilizer. To determine whether A. petiolata affected the abundance of understory competitors, we also removed A. petiolata from one treatment. A. petiolata that received early nutrients exhibited greater growth. Treatments receiving fall leaf litter or artificial nutrients had greater A. petiolata adult biomass than plots receiving spring nutrient additions (leaf litter or artificial nutrients). However, fall leaf litter addition had no effect on the richness of competitor species. Thus, wintergreen phenology may contribute to the spread of A. petiolata through deciduous forest understories, but may not explain community-level impacts of A. petiolata in deciduous forests.

Metabolic disorders have been established as major risk factors for ocular complications and poor vision. However, little is known about the inverse possibility that ocular disease may cause metabolic dysfunction. To test this hypothesis, we assessed the metabolic consequences of a robust dietary challenge in several mouse models suffering from retinal mutations. To this end, mice null for melanopsin (Opn4-/-), the photopigment of intrinsically photosensitive retinal ganglion cells (ipRGCs), were subjected to five weeks of a ketogenic diet. These mice lost significantly more weight than wild-type controls or mice lacking rod and cone photoreceptors (Pde6brd1/rd1). Although ipRGCs are critical for proper circadian entrainment, and circadian misalignment has been implicated in metabolic pathology, we observed no differences in entrainment between Opn4-/- and control mice. Additionally, we observed no differences in any tested metabolic parameter between these mouse strains. Further studies are required to establish the mechanism giving rise to this dramatic phenotype observed in melanopsin-null mice. We conclude that the causality between ocular disease and metabolic disorders merits further investigation due to the popularity of diets that rely on the induction of a ketogenic state. Our study is a first step toward understanding retinal pathology as a potential cause of metabolic dysfunction.

Nearly all bees rely on pollen as the sole protein source for the development of their larvae. The central importance of pollen for the bee life cycle should exert strong selection on their ability to locate the most rewarding sources of pollen. Despite this importance, very few studies have examined the influence of intraspecific variation in pollen rewards on the foraging decisions of bees. Previous studies have demonstrated that inbreeding reduces viability and hence protein content in Mimulus guttatus (seep monkeyflower) pollen and that bees strongly discriminate against inbred in favour of outbred plants. We examined whether variation in pollen viability could explain this preference using a series of choice tests with living plants, artificial plants and olfactometer tests using the bumble bee Bombus impatiens. We found that B. impatiens preferred to visit artificial plants provisioned with fertile anthers over those provisioned with sterile anthers. They also preferred fertile anthers when provided only olfactory cues. These bumble bees were unable to discriminate among live plants from subpopulations differing dramatically in pollen viability, however. They preferred outbred plants even when those plants were from subpopulations with pollen viability as low as the inbred populations. Their preference for outbred plants was evident even when only olfactory cues were available. Our data showed that bumble bees are able to differentiate between anthers that provide higher rewards when cues are isolated from the rest of the flower. When confronted with cues from the entire flower, their choices are independent of the quality of the pollen reward, suggesting that they are responding more strongly to cues unassociated with rewards than to those correlated with rewards. If so, this suggests that a sensory bias or some level of deception may be involved with advertisement to pollinators in M. guttatus.