Integrative And Comparative Biology

BackgroundLiving organisms face ubiquitous pathogenic threats and have consequently evolved immune systems to protect against potential invaders. However, many components of the immune system are physiologically costly to maintain and engage, often drawing resources away from other organismal processes such as growth and reproduction. Evidence from a diversity of systems has demonstrated that organisms use complex resource allocation mechanisms to manage competing needs and optimize fitness. However, understanding of resource allocation patterns is limited across taxa. Cnidarians, which include ecologically important organisms like hard corals, have been historically understudied in the context of resource allocations. Improving understanding of resource allocation-associated tradeoffs in cnidarians is critical for understanding future ecological dynamics in the face of rapid environmental change. MethodsHere, we characterize trade-offs between constitutive immunity and reproduction in the facultatively symbiotic coral Astrangia poculata. Male colonies underwent ex situ spawning and sperm output was quantified. We then examined the effects of variable symbiont density and energetic budget on physiological traits, including immune activity and reproductive investment. Furthermore, we tested for potential trade-offs between immune activity and reproductive investment. ResultsWe found limited effects of energetic budget on immune metrics; melanin production was significantly positively associated with energetic budget. However, we failed to document any associations between immunity and reproductive output which would be indicative of trade-offs, possibly due to experimental limitations. Our results provide a preliminary framework for future studies investigating immune trade-offs in cnidarians.

The honey bee colony (Apis mellifera) acts as a superorganism, with a dual immune system that operates at the individual and social level. However, the linkages between immune mechanisms across the two levels remain poorly understood, despite the relevance for developing effective breeding strategies to improve honey bee disease resistance. Hygienic behavior involving the removal of unhealthy brood is a key component of honey bee social immunity and is highly effective at limiting parasites and pathogens in the colony. While this form of hygienic behavior can reduce brood diseases, parasites infecting adult bees primarily, such as Nosema ceranae, are not directly impacted by the behavior. However, when using the Unhealthy Brood Odor (UBeeO) assay to quantify hygienic behavior performance, hygienic colonies have been shown to maintain lower Nosema spp. loads over time and overall compared to non-hygienic colonies. To investigate the mechanisms driving reduced Nosema spp. in hygienic colonies, we conducted a series of field and lab experiments to test the innate immune performance of individual bees. We evaluated several factors across hygienic and non-hygienic bees including (1) differences in N. ceranae infection levels, (2) survival probability, (3) Vitellogenin and Hymenoptaecin gene expression, and (4) amount of N. ceranae inoculant consumed. We found that hygienic bees consumed less of the inoculant, exhibited upregulated Vitellogenin gene expression at peak N. ceranae infection, showed a positive relationship between Hymenoptaecin gene expression and N. ceranae infection levels, and had greater survivability when infected with N. ceranae, compared to non-hygienic bees. Here, we present new findings that link colony hygienic behavior performance to individual-level resistance and tolerance mechanisms in response to N. ceranae, suggesting broader implications for the success of selective breeding programs targeting hygienic traits.

A broad class of animals rely on touch sensation for perception. Among insects, the American cockroach P. americana is a touch specialist that uses a pair of soft antennae with distributed sensors to touch its environment to guide decision making. During touch, forces on the antenna can activate thousands of mechanosensors. To understand the content of this sensory information, it is critical to understand how antenna mechanics shape the transmission of contact forces. Here, we investigate the mechanical behavior and morphology of the American cockroach antenna at the individual segment level through experiments, mathematical modeling, imaging with Micro-Computed Tomography (Micro-CT), 3D reconstruction of antenna morphology, and finite element modeling (FEM). Our experimental results and model predictions reveal that the antenna flagellum bends according to a kinematic chain model, with rigid segments connected by joints. Whereas the middle region of the antenna consistently fractured under cyclic bending, the tip region remained intact under large deformations, revealing mechanical specialization along the antenna. Micro-CT imaging revealed an invagination of the exocuticle at segment intersections of the tip. To test the hypothesis that this structure can enhance flexibility and robustness, we used FEM and confirmed that the invagination allows for larger bending without structural failure (buckling). Applying FEM to a morphologically accurate kinematic chain model of the flagellum revealed the relationship between the local strain at the location of marginal sensilla and intersegment angle, predicting the information available for antenna proprioception. Taken together, these findings reveal biomechanical adaptations of insect antennae and provide a critical step toward a mechanistic understanding of touch sensation in a touch specialist. SUMMARY STATEMENTBy combining experiments, imaging and modeling, we demonstrate distinct mechanical features in the cockroach antenna and provide a framework to model the neuromechanics of the antenna in an insect touch specialist.

The immune system is the primary defense against parasites. With the ever-increasing rate of disease, epidemiologic models considering geographic variation in immune responses could prove useful. Despite increasing interest in the macroecology of parasitism and infectious diseases, we know little about the macroecology of immune responses. Host characteristics, parasite exposure, and environmental factors can all affect immunity, but how these factors interact to shape spatial variation in the strength of immune responses remains unexplored. We captured odonates (dragonflies and damselflies) and their conspicuous ectoparasitic mites across a geographic area spanning the temperate and boreal forest biomes in eastern Canada. We then conducted immune response bioassays on 1,237 individuals from 63 odonate species. We used linear regressions and structural equation models to relate immune responses to host body size, parasite load, pH, temperature, and precipitation while accounting for evolutionary relationships among host species. We found significant differences in the strength of immune response among host individuals, and this variation was best explained by climatic conditions, specifically decreasing with precipitation and, to a lesser degree, temperature. While host species significantly differed in immune response strength, we found no effect of host body size, evolutionary relationships among hosts, or parasitism on immune response. Our study investigating the drivers of immune response across dozens of species spread across two biomes is the most comprehensive to date. Climatic conditions have a strong influence on host immune response, regardless of host characteristics or parasitism rates. In this specific case, strong immune responses were associated with low levels of annual precipitation, which could relate to the role of cuticular melanin content in desiccation resistance, and the melanin-based encapsulation response being a byproduct of this adaptation. A spatially-explicit understanding of the biological processes affecting immunity could improve epidemiological models of disease risk that inform disease management globally.

Laws of physics shape morphological and behavioral adaptations to locomotion at different body sizes. Water striders serve as a model taxon to study how simple physical constraints of water-surface habitats affect their behavior and morphology, and hydrodynamics of rowing by midlegs on the surface is well understood. However, the physics of the subsequent passive sliding has been less explored. We created a model of sliding on the water surface to simulate the effect of body mass, striding type, and wetted leg lengths on an insects ability to float on the surface and on the sliding resistance. The model predicts that to support their weight on the surface during sliding, the heavy species should either develop long forelegs that support the frontal part of its body during symmetrical striding (when two midlegs thrust) or use asymmetrical striding (when one forward-extended midleg supports the body while the other midleg and contra-lateral hindleg thrust). These predictions are confirmed by the behavior and morphology of various Gerridae species. Hence, the results illustrate how simple physical processes specific to a certain habitat type have far-reaching consequences for the evolution of morphological and behavioral diversification associated with body size among biological organisms in these habitats.

The surface structures of microtrichia on the hindwings of Verspa Crabro (European hornets) were observed by scanning electron microscopy (SEM). Helical grooves were seen in the microtrichia on both the ventral and dorsal sides. Their helical orientation varied spatially across the wing surface but were the same in the ventral and dorsal surfaces. Notably the grooves wound antipodally between the left and right wings. The observed chirality relation might be related to the effective anti-wetting of hindwings. The results demonstrated the importance of microscopic chirality in understrading the functions of insect wings.

Immune defense is comprised of 1) resistance: the ability to reduce pathogen load, and 2) tolerance: the ability to limit the disease severity induced by a given pathogen load. The study of tolerance in the field of animal immunity is fairly nascent in comparison to resistance. Consequently, studies which examine immune defense comprehensively (i.e., considering both resistance and tolerance in conjunction) are uncommon, despite their exigency in achieving a thorough understanding of immune defense. Furthermore, understanding tolerance in arthropod disease vectors is uniquely relevant, as tolerance is essential to the cyclical transmission of pathogens by arthropods. Here, we tested the effect(s) of dietary sucrose concentration (high or low) and blood meal (present or absent) on resistance and tolerance to Escherichia coli infection in the yellow fever mosquito Aedes aegypti. Resistance and tolerance were measured concurrently and at multiple timepoints. We found that both blood and sucrose affected resistance. Mosquitoes from the low sugar treatment displayed enhanced resistance at all timepoints post-infection compared to those from the high sugar treatment. Additionally, blood-fed mosquitoes showed enhanced resistance compared to non-blood-fed mosquitoes, but only on day 1 post-infection. Sucrose had no effect on tolerance, but the effect of blood was significant and dynamic across time. Specifically, we show that consuming blood prior to infection ameliorates a temporal decline in tolerance that mosquitoes experience when provided with only sugar meals. Taken together, our findings indicate that different dietary components can have unique and sometimes temporally dynamic impacts on resistance and tolerance. Finally, our findings 1) highlight the value of experimental and analytical frameworks which consider the explicit testing of effects on both resistance and tolerance as separate, but equally important, components of immune defense, and 2) underscore the importance of including a temporal component in studies of immune defense.

Overnutrition with dietary sugar can worsen infection outcomes in diverse organisms including insects and humans, generally through unknown mechanisms. In the present study, we show that adult Drosophila melanogaster fed high-sugar diets became more susceptible to infection by the Gram-negative bacteria Providencia rettgeri and Serratia marcescens, although diet had no significant effect on infection by Gram-positive bacteria Enterococcus faecalis or Lactococcus lactis. We found that P. rettgeri and S. marcescens proliferate more rapidly in D. melanogaster fed a high-sugar diet, resulting in increased probability of host death. D. melanogaster become hyperglycemic on the high-sugar diet, and we find evidence that the extra carbon availability may promote S. marcescens growth within the host. However, we found no evidence that increased carbon availability directly supports greater P. rettgeri growth. D. melanogaster on both diets fully induce transcription of antimicrobial peptide (AMP) genes in response to infection, but D. melanogaster provided with high-sugar diets show reduced production of AMP protein. Thus, overnutrition with dietary sugar may impair host immunity at the level of AMP translation. Our results demonstrate that dietary sugar can shape infection dynamics by impacting both host and pathogen, depending on the nutritional requirements of the pathogen and by altering the physiological capacity of the host to sustain an immune response. Author SummaryDiet has critical impact on the quality of immune defense, and high-sugar diets increase susceptibility to bacterial infection in many animals. Yet it is unknown which aspects of host and pathogen physiology are impacted by diet to influence infection dynamics. Here we show that high-sugar diets increase susceptibility to some, but not all, bacterial infections in Drosophila. We find that feeding on high sugar diet impairs the host immune response by reducing the level of antimicrobial peptides produced. The expression of genes encoding these peptides is not affected, so we infer that protein translation is impaired. We further show that flies on high-sugar diets are hyperglycemic, and that some pathogens may use the excess sugar in the host to promote growth during the infection. Thus, our study demonstrates that dietary impacts on infection outcome arise through physiological effects on both the host and pathogen.

Centimeter-scale fliers that combine wings with springy elements must contend with the high power requirements and mechanical constraints of flapping wing flight. Insects utilize elastic energy exchange to reduce the inertial costs of flapping wing flight and potentially match wingbeat frequencies to a mechanical resonance. Flying at resonance may be energetically favorable under steady conditions, but it is difficult to modulate the frequency of a resonant system. Evidence suggests that insects utilize frequency modulation over long time scales to adjust aerodynamic forces, but it remains an open question the extent to which insects can modulate frequency on the wingstroke-to-wingstroke timescale. If wingbeat frequencies deviate from resonance, the musculature must work against the elastic flight system, thereby potentially increasing energetic costs. To assess how insects address the simultaneous needs for power and control, we tested the capacity for wingstroke-to-wingstroke wingbeat frequency modulation by perturbing free hovering Manduca sexta with vortex rings while recording high-speed video at 2000 fps. Because hawkmoth flight muscles are synchronous, there is at least the potential for the nervous system to modulate frequency on each wingstroke. We observed {+/-} 16% wingbeat frequency modulation in just a few wing strokes. Via instantaneous phase analysis of wing kinematics, we found that over 85% of perturbation responses required active changes in motor input frequency. Unlike their robotic counterparts that explicitly abdicate frequency modulation in favor of energy efficiency, we find that wingstroke-to-wingstroke frequency modulation is an underappreciated control strategies that complements other strategies for maneuverability and stability in insect flight.

Insects show diverse flight kinematics and morphologies reflecting their evolutionary histories and ecological adaptations. Many silkmoths utilizing low wingbeat frequencies and large wings to fly display body oscillations: Their bodies pitch and bob periodically - synchronized with their wing flapping cycle. Similar oscillations in butterflies augment weight support and thrust and reduce flight power requirements. However, how the instantaneous body and wing kinematics interact for these beneficial aerodynamic and power consequences is not well understood. We hypothesized that the body oscillations affect aerodynamic power requirements by influencing the wing rotation relative to the airflow. Using three-dimensional forward flight video recordings of four silkmoth species and a quasi-steady blade-element aerodynamic method, we found that the body pitch angle and the wing sweep angle maintain a narrow range of phase differences to enhance the angle of attack variation between each half-stroke due to enhanced wing rotation relative to the airflow. This redirects the aerodynamic force to increase upward and forward force during downstroke and upstroke respectively thus lowering the overall drag without compromising weight support and forward thrust. A reduction in energy expenditure is beneficial because adult silkmoths do not feed and rely on limited energy budgets.

Many organisms across ecosystems track odor plumes to locate mates and food. In flying insects, the task of localizing an odor source is particularly challenging due to the complicated dynamics associated with wind flow and odor plume dispersion through spatially complex environments. Although wind tunnel experiments have been instrumental for answering many questions related to olfactory search, such experiments cannot replicate the complexity of natural wind conditions. Thus, our knowledge of how real-world wind characteristics influence insects success and strategies to locate odor sources remains an open area of investigation. Here, we tested whether certain wind conditions were more favorable for foraging insects by comparing yellowjacket arrival times and corresponding wind conditions across three distinct natural environments. Our results indicate that Vespula pensylvanica are capable of locating odor sources across the full range of observed wind conditions, without any clear preferences. This suggests that insects have adapted strategies to perform odor localization tasks across the full spectrum of natural wind that they may encounter. Our field-based approach provides insight into key considerations for future wind tunnel experiments which seek to better resolve insect plume tracking in understudied flow regimes.

Body size is the major factor to the flight mechanics in animals. To fly at low Reynolds numbers, miniature insects have adaptations in kinematics and wing structure. Many microinsects have bristled wings, which reduce inertia and power requirements when providing good aerodynamic efficiency. But both bristled and membranous-winged microinsects fly at Reynolds numbers of about 10. Yet, the kinematics of the smallest known membranous-winged species have not been studied sufficiently. The available data are limited to the forewings of a relatively large parasitoid wasp Encarsia formosa. We studied kinematics of wings and body and flight performance in one of the smallest membranous-winged wasps, Trichogramma telengai (0.5 mm body length, Re = 12). T. telengai reaches 29 cm s-1 speed and 7 m s-2 acceleration in horizontal flight which are comparable with the flight performance of other microinsects. The wingbeat cycle is characterized by high frequency (283 Hz) and stroke amplitude (149{degrees}) and includes U-shaped strokes at high angles of attack and prolonged clap-and-fling. The hindwings move with a slight phase shift and smaller amplitude than the forewings. T. telengai differs from large membranous-winged insects and miniature featherwing beetles in kinematics, but it is fundamentally similar to E. formosa (Re = 18, membranous wings) and thrips Frankliniella occidentalis (Re = 15, bristled wings). We showed that, at Re {approx} 101, both membranous and bristled-winged insects have sufficient flight performance. Further study of the bristled-winged insects will make it possible to define the size limits of effectiveness of different wing structures.

In the last 20 years, Pseudomonas entomophila (Pe) has emerged as a model to explore insect immunity to bacterial intestinal pathogens. Laboratory studies evidenced multiple detrimental effects of Pe on Drosophila melanogaster. However, these effects require that the bacteria are ingested in extremely high concentrations of 1010 - 1011 CFU per mL (OD600 20 - 200), questioning the relevance of this pathogen in nature. Here, we tested whether the need for such high doses may be due to protective effects of the food preservative methylparaben (Nipagin), a standard ingredient of artificial Drosophila diets. While significant mortality in flies fed diet containing standard methylparaben concentration required doses of >1010 CFU per mL, when methylparaben was absent we could observe mortality using 500,000x lower doses. Consistent with these results, we demonstrated strong bactericidal properties of methylparaben on Pe in vitro. In the absence of methylparaben even the smallest inocula (105 CFU per mL) led to high bacterial loads (106 CFU per fly) after several days, indicating the ability of Pe to grow and overcome the flies defenses. We also demonstrate that in the absence of methylparaben, infected flies could easily transmit the pathogen to other adults and to offspring, resulting in high mortality and thus highlighting the potential of Pe as a pathogen of Drosophila in nature. Our study also underscores that careful consideration should be given to food additives used in standard diets in laboratory research on host-pathogen interaction. ImportanceAccurate characterization of pathogen infections requires appropriate experimental methodologies. Infections of insects with Pe are frequently studied using fruit flies as a model organism, with laboratory cultures typically maintained on artificial media containing various food preservatives. In this study, we show that one commonly used preservative, methylparaben, significantly influences the outcome of oral infections with Pe. We found that minimal infection doses, far below the standards of the field, could be still lethal to flies raised on media without methylparaben. This increased virulence was also associated with increased transmission of the pathogen, both from infected adult flies to their offspring and to uninfected adults. Our findings show how subtle variations in experimental conditions can profoundly affect how we perceive pathogenic threats.

Insects demonstrate remarkable agility in flight despite constant changes in flight dynamics throughout their lives. However, it is unclear whether such resilience is conferred via purely feedback control or whether adaptive feedforward control mechanisms are present. This study examines whether adaptive feedforward control mechanisms are present in Drosophila melanogaster flight, by comparing the free-flight trajectories with and without wing damage and antennae ablation. Flies with partial wing excisions exhibited increased flight speeds in the dark compared to intact-wing controls. Upon exposure to visual contrast in light, the clipped-wing flies reduced their speed comparable to that of the control group flies. Notably, the lower speed persisted upon returning to the dark, indicating an enduring change to the flight controller. To discern between feedforward adaptation and a change in mechanosensory feedback gains, we replicated the experiment after ablating the antennal arista, the primary mechanosensors for sensing airspeed. Although flies with ablated antennae flew with greater variance in speed, they displayed a parallel trend in mean speed adaptation: increased speed in the dark, compensation in the light, and sustained lower speed in subsequent dark conditions. This consistent pattern strongly supports the involvement of adaptive feedforward control rather than the adjustment of mechanosensory feedback gains. Our investigation unveils an adaptive strategy in D. Melanogaster flight, illustrating its ability to set flight speed through adaptive feedforward control mechanisms.

Jumping can be hazardous for entomopathogenic nematodes (EPNs) as those that fail to attach to an insect host face death by predation or starvation. Recently, it has been shown that electrostatic charges on large insects can prompt a close-range detachment of free-living nematodes, which are non-parasitic and unable to jump. However, it remains unclear if static electricity can influence aerial interactions between parasitic jumping worms and their insect hosts. Here we analyze and model the trajectories of jumping EPNs in still air as they approach fruit flies with varying electrostatic charge. We discover that the nematodes attachment to the host is facilitated by an electrical potential of a few hundred volts, a magnitude commonly found in flying insects. A model combining electrostatics, aerodynamics, and Bayesian inference indicates that the electrostatic charge on jumping nematodes is [~] 0.1 pC, which aligns with theoretical predictions for electrostatic induction. Drag coefficients based on host-nematode interactions in the presence of horizontal wind show differences at both low and high jumping velocities. Numerical simulations show that intermediate wind speeds ([~] 0.2 m/s) can further increase the likelihood of host attachment, as wind-driven aerial drifting allows the worms to reach hosts at greater distances. Our results suggest that submillimeter parasites that become airborne may exploit the electric charge carried by their host to facilitate attachment and thus enhance survival. The use of quantitative physical models provides valuable insights into understanding complex airborne infectious diseases mediated by natural environmental forces. Significance StatementEntomopathogenic nematodes (EPNs) are submillimeter parasites renowned for their explosive aerial jumping, allowing them to reach distant insect hosts. They serve as important model organisms and natural biopesticides. Our work reveals that these tiny organisms can be electrostatically attracted to charged hosts, such as fruit flies, increasing the likelihood of infection. Experiments show that host attachment is significantly enhanced by electrostatic forces generated by naturally occurring electric fields from flying insect hosts. Our computational model confirms that the static charge of EPNs agrees with theoretical predictions from electrostatic induction. We propose that electrostatics play a crucial role in enhancing the survival of these jumping parasites and provide a framework for modeling environmental forces in aerial parasite-host interactions.

Cephalopods are highly versatile predators, with many species using suckers to capture their prey. These suckers attach to substrates ranging from the stiff, rough exoskeletons of crustaceans to the soft, smooth mucosal tissues of other cephalopods. Despite generating higher suction pressures than octopuses, less attention has been given to the biomechanics of cuttlefish suckers. Cuttlefish suckers exhibit a stiff, rough papillated rim that acts as a seal when in contact with a substrate. We hypothesise that these rim papillae have evolved to attach to rough substrates that match their own rugosity and to prevent the trapping of water at the contact interface, which occurs for soft interfaces underwater. To test this hypothesis, we investigated the passive attachment performance of common cuttlefish (Sepia officinalis) suckers ex vivo on a variety of artificial substrates that differed in both stiffness and roughness. We found that suckers generated larger attachment forces on stiffer substrates. Furthermore, sucker attachment forces varied significantly with substrate roughness, where highest attachment forces occurred on substrate roughnesses that coincided with the average sucker papillae size ([~]6.33 m RMS). These findings indicate that the papillae morphology may be associated with attachment performance, and could inform the design and development of versatile, bioinspired suction cups. Summary StatementCuttlefish suction cups have microscopic pillars that may interact with rough or soft surfaces to improve adhesion. We systematically examine this hypothesis using a pull-off experiment and a mathematical model.

Insects regulate their body temperature mostly behaviourally, by changing posture or microhabitat. These strategies may be ineffective in some habitats, for example on carrion. Carrion beetles create a feeding matrix by applying to cadaver surface anal or oral exudates. We tested the hypothesis that the matrix, which is formed on carrion by communally breeding beetle Necrodes littoralis L. (Silphidae), produces heat that enhances insect fitness. Using thermal imaging we demonstrate that heat produced in the matrix formed on meat by adult or larval beetles is larger than in meat decomposing without insects. Larval beetles regularly warmed up in the matrix. Moreover, by comparing matrix temperature and larval fitness in colonies with and without preparation of meat by adult beetles, we provide evidence that formation of a matrix by adult beetles has deferred thermal effects for larval microhabitat. We found an increase in heat production of the matrix and a decrease in development time and mortality of larvae after adult beetles applied their exudates on meat in the pre-larval phase. Our findings indicate that spreading of exudates over carrion by Necrodes larvae, apart from other likely functions (e.g. digesting carrion or promoting growth of beneficial microbes), facilitates thermoregulation. In case of adult beetles, this behaviour brings distinct thermal benefits for their offspring and therefore may be viewed as a new form of indirect parental care with an important thermal component.

Bumblebees rely on visual memories acquired during the first outbound flights to relocate their nest. While these learning flights have been extensively studied in sparse environments with few objects, little is known about how bees adapt their flight in more dense, cluttered, settings that better mimic their natural habitats. Here we investigated how environmental complexity influences the first outbound flights of bumblebees. In a large arena we tracked the bees 3D positions to examine the flight patterns, body orientations, and nest fixations across environmental conditions characterised by different object constellations around the nest entrance. In cluttered environments, bees prioritised altitude gain over horizontal distance, suggesting a strategy to overcome obstacles and visual clutter. Body orientation patterns became more diverse in dense environments, indicating a balance between nest-oriented learning and obstacle avoidance. Notably, bees consistently preferred to fixate the location of the nest entrance from elevated positions above the dense environment across all conditions. Our results reveal significant changes in the 3D flight structure, body orientations, and nest fixation behaviours as object density increases. This highlights the importance of considering 3D space and environmental complexity in understanding insect navigation.

In buzz-pollinated plants, bees apply vibrations produced by their thoracic muscles to the flower, causing pollen release from anthers, often through small apical pores. During floral buzzing, bees grasp one or more anthers with their mandibles, and vibrations are transmitted to the focal anther(s), adjacent anthers, and the whole flower. Because pollen release depends on the vibrations experienced by the anther, the transmission of vibrations through flowers with different morphologies may determine patterns of release, affecting both bee foraging and plant fitness. Anther morphology and intra-floral arrangement varies widely among buzz-pollinated plants. Here, we compare the transmission of vibrations among focal and non-focal anthers in four species with contrasting anther morphologies: Cyclamen persicum (Primulaceae), Exacum affine (Gentianaceae), Solanum dulcamara and S. houstonii (Solanaceae). We used a mechanical transducer to apply bee-like artificial vibrations to focal anthers, and simultaneously measured the vibration frequency and displacement amplitude at the tips of focal and non-focal anthers using high-speed video analysis (6,000 frames per second). In flowers in which anthers are tightly held together (C. persicum and S. dulcamara), vibrations in focal and non-focal anthers are indistinguishable in both frequency and displacement amplitude. In contrast, flowers with loosely arranged anthers (E. affine) including those in which stamens are morphologically differentiated within the same flower (heterantherous S. houstonii), show the same frequency but higher displacement amplitude in non-focal anthers compared to focal anthers. Our results suggest that stamen arrangement affects vibration transmission with potential consequences for pollen release and bee behaviour.

Animals use social information gathered by observing other individuals to adjust their behavior to better match the environment and improve fitness. Many insects use social information in various contexts. Bees improve their foraging efficiency by using social information from conspecifics to gauge nectar availability. Bees frequently encounter various heterospecific flower visitors, including those from different trophic groups such as nectaring predators. These heterospecifics may provide valuable information about nectar availability. We determined how bumble bees (Bombus impatiens) use visual social information from lady beetles (Hippodamia convergens). Lady beetles are predators of small insects, but not bees, and also visit flowers to consume floral nectar to increase their reproductive output. Using laboratory-maintained bumble bees freely flying in arenas, we tested if bees could (1) innately recognize lady beetles as sources of social information about nectar, and (2) learn to use lady beetles to gauge nectar availability. Bees did not innately recognize lady beetles as a source of social information. They correctly learned to associate conspecifics with the presence and absence of food, but learned to associate lady beetles only with the presence of food and not the absence. Our results demonstrate social learning across species and trophic guilds, but suggest limits to when and how bees generalize social information from diverse heterospecific flower visitors.