Biology subjects

Vannette, R. L.

Publications and source records attributed to Vannette, R. L..

18 recordsLinked to original sources

bioRxiv2026

Supplemental water modulates pollinator visitation on resource-rich plant species

Urban green spaces provide important floral resources for pollinators, and supplemental watering can improve the abundance and quality of these resources. However, increasing frequency and intensity of drought under climate change create tradeoffs between ecological benefits and water conservation. Manipulating the timing and duration of irrigation may offer a way of enhancing floral traits that support pollinator communities while moderating water use. Focusing on two resource-rich native plant species, Phacelia californica and Helenium puberulum, we examined how the addition of supplemental water in spring and summer affects floral traits and pollinator visitation. We examined mechanisms that may govern the effects of supplemental watering on pollinator visitation, namely the number of flowers, nectar volume, nectar sucrose concentration, and corolla length. Overall, plant individuals receiving more water were visited by more pollinators. In both plant species, this was apparently mediated by floral abundance; individual plants with more flowers received more visitors, though effects of watering varied slightly between the two plant species and the insect visitor taxa. Water additions in spring increased pollinator visitation per plant on P. californica, but visitation rates per flower did not differ among treatments. Responses among pollinator groups varied, with effects driven primarily by sweat bees (family: Halictidae) and bumble bees (Bombus species), while honeybee visitation was consistent across treatments. Our results suggest that insects prefer to visit supplementally watered P. californica plants. Because honeybee visitation did not vary by treatment, supplemental water may disproportionately benefit native pollinators, including bumblebees, which are imperiled. Similar to P. californica, Helenium puberulum plants watered in spring and summer had the most flowers and the most floral visitors per plant and per flower. Spring-watering H. puberulum did not have a significant effect on flower production but did increase insect visitation per flower. Overall, our results emphasize that irrigation and other avenues of water addition are key drivers of flower production and insect visitation, such that homeowners who wish to conserve water must weigh effects on pollinators with the need to conserve water in arid climates.

ecology↗

bioRxiv2026

Heatwaves do not impact bacteria within pollen provisions, despite accelerating blue orchard bee (Osmia lignaria) larval development

Many insect populations are experiencing thermal stress as a result of global change, making it imperative to investigate how their relationship with other organisms will be impacted by heat disturbances. Microbial symbionts, such as bacteria, have the potential to enhance or inhibit an insect's thermal tolerance. Solitary bee larvae host bacteria within their food stores ("pollen provisions"), which have been shown to benefit survival and development; however, it is unclear how heatwaves brought about by climate change will impact their relationships with these bacterial partners. In this study, we subjected blue orchard bee (Osmia lignaria) eggs and larvae to a 4-day heatwave (35 {degrees}C daytime:22 {degrees}C nighttime) or kept them at control temperatures (25 {degrees}C daytime:15 {degrees}C nighttime), then returned all bees to control temperatures for a 5-day recovery period. We assessed bacterial communities within pollen provisions and larval development stage pre-heatwave (Day 0), immediately post-heatwave (Day 4), and following the recovery period (Day 9). Bacterial community composition, diversity, and abundance were resilient to heat stress, but larval bees developed faster when subjected to a heatwave. This finding refutes the hypothesis that bacteria within pollen provisions modulate blue orchard bee responses to heat, suggesting instead that developmental effects could be more largely shaped by bee physiology or interactions with microorganisms other than bacteria.

ecology↗

bioRxiv2025

Bee Microbiomes Harbor Diverse Antimicrobial Resistance Genes on Plasmids

Antimicrobial resistance (AMR) is an emerging public health threat. In North America, tetracycline and macrolide antibiotics are often used to prevent or treat bacterial infections in honey bees. Previous research has shown that this practice has led to widespread drug resistance in honey bee gut microbiomes. However, where bee-associated bacteria encode AMR, genomically or on mobile genetic elements, is less well understood. Moreover, how the abundance, diversity, and mechanism of AMR differs between managed honey bees and other bees remains largely unexplored. Here we use existing metagenomic data from two previous studies to profile the AMR genes associated with managed honey bees, commercially produced bumble bees, and wild bumble bees. Our results suggest that honey bee associated bacteria house a greater diversity of AMR genes, specifically on plasmids, compared to bumble bees. In addition, we show that honey and bumble bee bacteria likely develop resistance to tetracyclines via different mechanisms. Overall, this study showcases how agricultural management has shaped the AMR genes associated with bees, and offers insights into the ecological context of differential AMR evolution within host-associated systems.

microbiology↗

bioRxiv2025

Contribution of floral transmission to the assembly and health impact of bacterial communities in watermelon seeds

Flower-sourced assembly of seed microbiota remains an understudied ecological process. Here, we investigated the floral transmission pathway for bacterial acquisition by developing seeds of watermelon (Citrullus lanatus). Comparison of stigma- and seed-associated bacterial communities from field-grown C. lanatus revealed significant overlap: up to 40% of the bacterial diversity that was detected in seed was also found on stigmas. In a field pollinator exclusion experiment, honeybee visitation to flower stigmas had no significant effect on bacterial community composition in seeds. Among a collection of bacterial isolates from stigmas and seeds in the field, more than half (57%) were able to transmit to seeds after inoculation onto stigmas under laboratory conditions. Interestingly, for most bacterial strains, fruit set rates increased after floral inoculation, and in some cases even in the absence of transmission to the seed. We also found that bacterial isolates from watermelon stigmas and seeds had variable (i.e. positive or negative) effects on seed germination and seedling emergence. Our findings highlight the contribution of floral transmission to seed microbiota assembly and its consequences for plant fitness.

ecology↗

bioRxiv2024

Niche-Based Priority Effects Predict Microbe Resistance to Erwinia amylovora in Pear Nectar

Fire blight is a devastating disease affecting pome fruit trees that is caused by Erwinia amylovora and leads to substantial annual losses worldwide. While antibiotic-based management approaches like streptomycin can be effective, there are concerns over evolved resistance of the pathogen and non-target effects on beneficial microbes and insects. Using microbial biological control agents (mBCAs) to combat fire blight has promise, but variable performance necessitates the discovery of more effective solutions. Here we used a niche-based predictive framework to assess the strength of priority effects exerted by prospective mBCAs, and the mechanisms behind growth suppression in floral nectar. Through in vitro and in vivo assays, we show that antagonist impacts on nectar pH and sucrose concentration were the primary predictors of priority effects. Surprisingly, overlap in amino acid use, and the degree of phylogenetic relatedness between mBCA and Erwinia did not significantly predict pathogen suppression in vitro, suggesting that competition for limited shared resources played a lesser role than alterations in the chemical environment created by the initial colonizing species. We also failed to detect an association between our measures of in vitro and in vivo Erwinia suppression, suggesting other mechanisms may dictate mBCA establishment and efficacy in flowers, including priming of host defenses.

plant biology↗

bioRxiv2024

Targeted Viromes and Total Metagenomes Capture Distinct Components of Bee Gut Phage Communities

Despite being among the most abundant biological entities on earth, bacteriophage (phage) remain an understudied component of host-associated systems. One limitation to studying host-associated phage is the lack of consensus on methods for sampling phage communities. Here, we compare paired total metagenomes and viral size fraction metagenomes (viromes) as methods for investigating the dsDNA viral communities associated with the GI tract of two bee species: the European honey bee Apis mellifera and the eastern bumble bee Bombus impatiens. We find that viromes successfully enriched for phage, thereby increasing phage recovery, but only in honey bees. In contrast, for bumble bees, total metagenomes recovered greater phage diversity. Across both bee species, viromes better sampled low abundance and low occupancy phage, while total metagenomes were biased towards sampling temperate phage and the most prominent phage. Additionally, many of the phage captured by total metagenomes were absent altogether from viromes. Comparing between bees, we show that phage communities in commercially reared bumble bees are significantly reduced in diversity compared to honey bees, likely reflecting differences in bacterial titer and diversity. In a broader context, these results highlight the complementary nature of total metagenomes and targeted viromes, especially when applied to host-associated environments. Overall, we suggest that studies interested in assessing total communities of host-associated phage should consider using both approaches. However, given the constraints of virome sampling, total metagenomes may serve to sample phage communities with the understanding that they will preferentially sample dominant and temperate phage.

microbiology↗

bioRxiv2023

Nontarget impacts of neonicotinoids on nectar-inhabiting microbes

Plant-systemic neonicotinoid (NN) insecticides can exert non-target impacts on organisms like beneficial insects and soil microbes. NNs can affect plant microbiomes, but we know little about their effects on microbial communities that mediate plant-insect interactions, including nectar-inhabiting microbes (NIMs). Here we employed two approaches to assess impacts of NN exposure on several NIM taxa. First, we assayed in vitro effects of six NN compounds on NIM growth using plate assays. Second, we inoculated a standardized NIM community into nectar of NN-treated canola (Brassica napus) and assessed survival and growth after 24 hours. With few exceptions, in vitro NN exposure tended to decrease bacterial growth metrics. However, the magnitude of decrease and the NN concentrations at which effects were observed varied substantially across bacteria. Yeasts showed no consistent in vitro response to NNs. In nectar, we saw no effects of NN treatment on NIM community metrics. Rather, NIM abundance and diversity responded to inherent plant qualities like nectar volume. In conclusion, we found no evidence NIMs respond to field-relevant NN levels in nectar within 24 h, but our study suggests that context, specifically assay methods, time, and plant traits, is important in assaying effects of NN on microbial communities.

microbiology↗

bioRxiv2023

Microbial Metamorphosis: Symbiotic bacteria and fungi proliferate during diapause and may enhance overwintering survival in a solitary bee

Host-microbe interactions underlie the development and fitness of many macroorganisms including bees. While many social bees benefit from vertically transmitted gut bacteria, solitary bees, which comprise the vast majority of species diversity within bees, lack a specialized gut microbiome. Here we examine the composition and abundance of bacteria and fungi throughout the complete life cycle of a ground-nesting solitary bee Anthophora bomboides standfordiana. In contrast to expectations, immature bee stages maintain a distinct core microbiome consisting of Actinobacteria and fungi in the genus Moniliella. Diapausing larval bees hosted the most abundant and distinctive bacteria and fungi, attaining 33 and 52 times their initial copy number, respectively. We tested two adaptive hypotheses regarding microbial functions for overwintering bees. First, using isolated bacteria and fungi, we found that Streptomyces from brood cells inhibited the growth of multiple pathogenic filamentous fungi, suggesting a role in pathogen protection during the long period of diapause. Second, sugar alcohol composition changed in tandem with major changes in microbial abundance suggesting links with bee metabolism or overwintering biology. Our results suggest that Anthophora bomboides hosts a conserved core microbiome that may provide key fitness advantages through larval development and overwintering, and raises the question of how this microbiome is transmitted between generations. The present work suggests that focus on adult gut microbiomes in solitary bees may overlook microbial symbionts within brood cells that could play diverse roles in bee fitness, and that exploration of microbes associated with immature bees may uncover novel microbial effects on insect hosts.

ecology↗

bioRxiv2023

Dispersal overwhelms variation in host quality to shape nectar microbiome assembly.

O_LIEpiphytic microbes frequently impact plant phenotype and fitness, but effects depend on microbe community composition. Deterministic filtering by plant traits and dispersal-mediated processes can affect microbiome assembly yet their relative contribution is poorly understood. C_LIO_LIWe tested the impact of host-plant filtering and dispersal limitation on nectar microbiome abundance and composition. We inoculated bacteria and yeast into 30 plants across 4 phenotypically distinct cultivars of Epilobium canum. We compared the growth of inoculated communities to openly visited flowers from a subset of the same plants. C_LIO_LIThe abundance and composition of microbial communities differed among plant individuals and cultivars in both inoculated and open flowers. However, plants hosting the highest microbial abundance when inoculated did not have the highest abundances when openly visited. Rather microbial density among open flowers was correlated with pollen receipt, a proxy for animal visitation, suggesting a primary role of deterministic dispersal in floral microbiome assembly despite variation in host-quality. C_LIO_LIWhile host-quality can affect microbiome assembly, variation in dispersal was more important here. Host quality could drive microbial community assembly in plant tissues where species pools are large and dispersal is consistent, but dispersal may be more important when microbial dispersal is limited, or arrival order is important. C_LI

ecology↗

bioRxiv2022

Plant species within Streptanthoid Complex associate with distinct microbial communities that shift to be more similar under drought

Prolonged water stress can reduce plant growth and fitness and may shift rhizoplane microbial communities. Although drought affects microbial structure of many plant species, it is still poorly understood whether closely related plant species host distinct microbial communities or respond similarly to drought. To explore this question, eight members of the Streptanthus clade with varying affinity to serpentine were subjected to three watering regimes. Rhizoplane bacterial communities were described using 16S rRNA gene amplicon sequencing and we explored the impact of watering treatment and plant species on alpha diversity, differential abundance, and beta diversity of soil bacterial communities. Among most plant species, reduced watering also reduced alpha diversity, but plant species did not strongly impact alpha diversity. Drought treatment reduced microbial community dissimilarity among samples: bacterial communities were more similar when plants received less water. Watering altered the relative abundance of bacterial genera within Proteobacteria, Firmicutes, Bacteroidetes, Planctomycetes, and Acidobacteria, which responded similarly in the rhizoplane of most plant species. These results suggest that prolonged water stress in Streptanthus spp. can result in convergent microbial communities among plant species. We suggest the functional consequences of these shifts be examined to assess effects on plant and microbial fitness under drought conditions.

genomics↗

bioRxiv2022

Nectar compounds impact bacterial and fungal growth and shift community dynamics in a nectar analog

Floral nectar is frequently colonized by fungi and bacteria. However, within individual flowers, nectar microbial communities are typically species-poor and dominated by few cosmopolitan genera. One hypothesis is that nectar constituents may act as a strong environmental filter. Non-sugar constituents in nectar could affect species composition via broad antimicrobial activity or differential effects on nectar microbial species. Here, we tested how five non-sugar nectar compounds as well as elevated sugar impacted the growth of 12 fungal and bacterial species isolated from flowers, pollinators, and the environment. We hypothesized that microbes isolated from nectar would be better able to grow in the presence of these compounds. Additionally, to test if nectar compounds could affect the outcome of competition among microbial taxa, we grew a subset of microbes in co-culture assays across a subset of treatments. We found that some compounds such as H2O2 broadly suppressed microbial growth across many but not all microbes tested. Other tested compounds were more specialized in the microbes they impacted. As hypothesized, the nectar specialist Metschnikowia reukaufii was unaffected by most nectar compounds assayed. However, many non-nectar specialist microbes remained unaffected by compounds thought to reduce microbial growth in nectar. Our results show that nectar chemistry can influence nectar microbial communities but that microbe-specific responses to nectar compounds are common. Nectar chemistry also affected the outcome of species interactions among microbial taxa, suggesting that non-sugar compounds in nectar can affect microbial community assembly and abundance in flowers.

microbiology↗

bioRxiv2021

Thermal sensitivity and seasonal change in the gut microbiome of a desert ant, Cephalotes rohweri

Microorganisms within ectotherms must withstand the variable body temperatures of their hosts. Shifts in host body temperature resulting from climate change have the potential to shape ectotherm microbiome composition. Microbiome compositional changes occurring in response to temperature in nature have not been frequently examined, restricting our ability to predict microbe-mediated ectotherm responses to climate change. In a set of field-based observations, we characterized gut bacterial communities and thermal exposure across a population of desert arboreal ants (Cephalotes rohweri). In a paired growth chamber experiment, we exposed ant colonies to variable temperature regimes differing by 5 {degrees}C for three months. We found that the abundance and composition of ant-associated bacteria were sensitive to elevated temperatures in both field and laboratory experiments. We observed a subset of taxa that responded similarly to temperature in the experimental and observational study, suggesting a role of seasonal temperature and local temperature differences amongst nests in shaping microbiomes within the ant population. Bacterial mutualists in the genus Cephalotococcus (Opitutales: Opitutaceae) were especially sensitive to change in temperature--decreasing in abundance in naturally warm summer nests and warm growth chambers. We also report the discovery of a member of the Candidate Phlya Radiation (Phylum: Gracilibacteria), a suspected epibiont, found in low abundance within the guts of this ant species.

microbiology↗

bioRxiv2021

Bee-associated fungi mediate effects of fungicides on bumble bees

Bumble bees are important pollinators that face threats from multiple sources, including agrochemical application. Declining bumble bee populations have been linked to fungicide application, which could directly affect the fungi often found in the stored food and GI tract of healthy bumble bees. Here, we test the hypothesis that fungicides impact bee health by disrupting bee-fungi interactions. We examine the interactive effects of the fungicide propiconazole and fungal supplementation on the survival, reproduction, and microbiome composition of microcolonies (queenless colonies) using two species, Bombus vosnesenskii and B. impatiens. We found that both bee species benefitted from fungi, but were differentially affected by fungicides. In B. vosnesenskii, fungicide exposure decreased survival while fungal supplementation mitigated fungicide effects. For B. impatiens, fungicide application had no effect, but fungal supplementation improved survival and offspring production. Fungicides reduced fungal abundance in B. vosnesenskii microcolonies, but not in B. impatiens, where instead fungal addition decreased fungal abundance. In B. vosnesenskii, the abundance of the pathogen Ascosphaera was negatively associated with survival, while the yeast Zygosaccharomyces was positively associated with survival. Our results highlight species-specific differences in response to fungicides and the nature of bee-fungi associations, and caution the use of results obtained using one species to predict responses of other species. These results demonstrate that fungicides can alter bee-fungi interactions with consequences for bee survival and reproduction, and suggest that exploring the mechanisms of such interactions, including interactions among fungi in the bee GI tract, may offer insights into bumble bee biology and conservation strategies. Significance statementWild bumble bee populations are declining globally, and a major predictor of these declines is agricultural fungicide application. We test the hypothesis that bee-associated fungi mediate fungicide effects on bees, examining how fungicide exposure and subsequent fungal supplementation impact bumble bee survival and microbiome. Fungal supplementation enhanced survival in both bumble bee species tested here, with fungi mediating effects of fungicide exposure in one species. Differences in bee survival were associated with changes in the gut mycobiome: negatively with the pathogen Ascosphaera and positively with Zygosaccharomyces yeasts. This study highlights the importance of the mycobiome in bumble bee health both as a mechanism by which fungicides impact bumble bees and as an avenue of further research on beneficial bee-associated fungi.

ecology↗

bioRxiv2020

Ecological dynamics of the almond floral microbiome in relation to crop management and pollination

O_LICrop tissues harbor microbiomes that can affect host health and yield. However, processes driving microbiome assembly, and resulting effects on ecosystem services, remain poorly understood. This is particularly true of flowering crops that rely on pollinators for yield. C_LIO_LIWe assessed effects of orchard management tactics and landscape context on the flower microbiome in almond, Prunus dulcis. Fourteen orchards (5 conventional, 4 organic, 5 habitat augmentation) were sampled at two bloom stages to characterize bacterial and fungal communities associated with floral tissues. The surveys were complemented by in vitro experiments to assess effects of arrival order and fungicides on nectar microbial communities, and effects of fungicides and microbes on honey bee foraging. Finally, a field trial was conducted to test effects of fungicides and microbes on pollination. C_LIO_LIAs bloom progressed, bacterial and fungal abundance and diversity increased, across all floral tissue types and management strategies. The magnitude by which microbial abundance and diversity were affected varied, with host proximity to apiaries and orchard management having notable effects on bacteria and fungi, respectively. C_LIO_LIExperiments showed immigration history and fungicides affected the composition of nectar microbial communities, but only fungicides affected pollinator foraging through reduced nectar removal. Neither treatment affected pollination services. C_LIO_LISynthesis and applications. Our results shed light on routes through which management practices can shape microbiota associated with flowers of a pollinator-dependent crop. With growing appreciation for the role of floral-associated microbes in affecting biotic interactions at the floral interface, understanding such drivers can potentially inform microbial-derived ecosystem services in agricultural landscapes, including pollination and biocontrol. C_LI

ecology↗

bioRxiv2019

Linked networks reveal dual roles of insect dispersal and species sorting for bacterial communities in flowers

Due to the difficulty of tracking microbial dispersal, it rarely possible to disentangle the relative importance of dispersal and species sorting for microbial community assembly. Here, we leverage a detailed multilevel network to examine drivers of bacterial community assembly within flowers. We show that plant species with similar visitor communities tend to have similar bacterial communities, and visitor identity to be more important than dispersal rate in structuring floral bacterial communities. However, plants occupied divergent positions in plant-insect and plant-microbe networks, suggesting an important role for species sorting. Taken together, our analyses suggest dispersal is important in determining similarity in microbial communities across plant species, but not as important in determining structural features of the floral bacterial network. A multilevel network approach thus allows us to address features of community assembly that cannot be considered when viewing networks as separate entities.

ecology↗

bioRxiv2019

Organic management promotes natural pest control through enhanced plant resistance to insects

Lower insect pest populations found on long-term organic farms have largely been attributed to increased biodiversity and abundance of beneficial predators. However, potential induction of plant defenses has largely been ignored. This study aims to determine whether host plant resistance mediates decreased pest populations in organic systems, and to identify the underpinning mechanisms. We demonstrate that greater numbers of leafhoppers (Circulifer tenellus) settle on tomatoes (Solanum lycopersicum) grown using conventional management as compared to organic. Soil microbiome sequencing, chemical analysis, and transgenic approaches, coupled with multi-model inference, suggest that changes in leafhopper settling between organically and conventionally-grown tomatoes are dependent on salicylic acid accumulation in the plant, likely mediated by rhizosphere microbial communities. These results suggest that organically-managed soils and microbial communities may play an unappreciated role in reducing plant attractiveness to pests by increasing plant resistance.

plant biology↗

bioRxiv2019

Microbial metabolites mediate bumble bee attraction and feeding

Animals such as bumble bees use chemosensory cues to localize and evaluate essential resources. Increasingly, it is recognized that microbes can alter the quality of foraged resources and produce metabolites that act as foraging cues. The distinct nature of these sensory cues however and their use in animal foraging remain poorly understood. Here, we test the hypothesis that species of nectar-inhabiting microbes differentially influence pollinator attraction and feeding via microbial metabolites in nectar. We examined electrophysiological potential of bumble bee antennae to respond to volatile microbial metabolites, followed by behavioral responses using choice assays. We assessed gustatory responses through both no-choice and choice feeding assays. Antennae responded to some microbial volatiles, and bees chose Asaia bacterial solutions compared to Metschnikowia yeast based on volatiles alone. However, B. impatiens consumed significantly more Metschnikowia-inoculated nectar, suggesting distinct roles for volatile and non-volatile microbial metabolites in mediating feeding decisions, with potential to affect associative learning and future foraging. Our results suggest that microbial metabolites may represent non-reinforcing cues with potential consequences for forager learning, economics and floral host reproduction.

ecology↗

bioRxiv2018

Plant species and soil type influence rhizosphere bacterial composition and seedling establishment on serpentine soils

Root-associated microbial communities influence plant phenotype, growth and local abundance, yet the factors that structure these microbial communities are still poorly understood. California landscapes contain serpentine soils, which are nutrient-poor and high in heavy metals, and distinct from neighboring soils. Here, we surveyed the rhizoplane of serpentine-indifferent plants species growing on serpentine and non-serpentine soils to determine the relative influence of plant identity and soil chemistry on rhizoplane microbial community structure using 16S rRNA metabarcoding. Additionally, we experimentally examined if locally adapted microorganisms enhance plant growth in serpentine soil. Plant species, soil chemistry, and the interaction between them were important in structuring rhizoplane bacterial communities in both the field and experimental soils. In the experiment, rhizoplane microbial community source influenced seedling survival, but plant growth phenotypes measured were largely invariant to microbial community with a few exceptions. Results from the field sampling suggest that plant species associate with specific microbial communities even across chemically distinct soils, and that microbial communities can differentially influence seedling survival on harsh serpentine soils.

microbiology↗