In many systems, host–parasite evolutionary dynamics have led to the emergence and maintenance of diverse parasite and host genotypes within the same population. Genotypes vary in key attributes: ...Parasite genotypes vary in ability to infect, host genotypes vary in susceptibility, and infection outcome is frequently the result of both parties' genotypic identities. These host–parasite genotype-by-genotype (GH × GP) interactions influence evolutionary and ecological dynamics in important ways. Interactions can be produced through genetic variation; however, here, we assess the role of variable gene expression as an additional source of GH × GP interactions. The bumblebee Bombus terrestris and its trypanosome gut parasite Crithidia bombi are a model system for host–parasite matching. Full-transcriptome sequencing of the bumblebee host revealed that different parasite genotypes indeed induce fundamentally different host expression responses and host genotypes vary in their responses to the infecting parasite genotype. It appears that broadly and successfully infecting parasite genotypes lead to reduced host immune gene expression relative to unexposed bees but induce the expression of genes responsible for controlling gene expression. Contrastingly, a poorly infecting parasite genotype induced the expression of immunologically important genes, including antimicrobial peptides. A targeted expression assay confirmed the transcriptome results and also revealed strong host genotype effects. In all, the expression of a number of genes depends on the host genotype and the parasite genotype and the interaction between both host and parasite genotypes. These results suggest that alongside sequence variation in coding immunological genes, variation that controls immune gene expression can also produce patterns of host–parasite specificity.
Production of many flowering crops often benefits from elevated pollinator diversity and abundance. Nevertheless, the opposite relationship may arise if bees impair fruit or seed production and/or ...quality by damaging flowers during visitation, despite transferring pollen. We assessed pollination and drupelet set (i.e. the number of drupelets per fruit) in 16 raspberry Rubus idaeus fields along a gradient of bee abundance in north‐west Patagonia, Argentina. Using pollen supplementation, we also tested whether drupelet set was pollen limited in a subset of six fields. Managed Apis mellifera and the invasive bumblebee Bombus terrestris accounted for 50% and 45% of all bee visits, respectively, to raspberry flowers. Pollen loads on stigmas increased with visit frequency of all bees combined and particularly with visitation by A. mellifera, but not by B. terrestris. Drupelet set was not pollen limited along the gradient of bee abundance. Instead, drupelet set decreased with the proportion of damaged styles, which varied more strongly with the frequency of visits by B. terrestris than by A. mellifera. In fields with the highest bee frequency of visits (~300 visits flower⁻¹ day⁻¹), ~80% of styles were damaged in flowers and these developed into fruits with ~30% fewer drupelets compared to flowers in fields with the lowest bee visitation rates (~4 visits flower⁻¹ day⁻¹). Synthesis and applications. Extreme bee visitation, particularly by Bombus terrestris, damaged the styles of raspberry flowers, precluding ovule fertilization by deposited pollen and limiting crop production by reducing drupelet set. Only a few bee visits are required to maximize fruit production in raspberry plants, therefore, pollinator management in north‐west Patagonia should focus principally on reducing the abundance of the invasive bumblebee B. terrestris and secondarily controlling the number of honeybee hives in nearby cultivated fields. Although mainstream pollinator management relies on the assumption that more visits enhance fruit set, high bee visitation rates can be detrimental for fruit development and, consequently, for crop yield.
Abstract
Reduced water availability can cause physiological stress in plants that affects floral development leading to changes in floral morphology and traits that mediate interactions with ...pollinators. As pollinators can detect small changes in trait expressions, drought-induced changes in floral traits could affect pollinator visitations. However, the linkage between changes in floral traits and pollinator visitations under drought conditions is not well explored. We, therefore, tested whether drought-induced changes in floral morphology and abundance of flowers are linked to changes in pollinator visitations. We conducted flight cage experiments with a radio frequency identification system for automated visitation recordings with bumble bees (Bombus terrestris) and common charlock (Sinapis arvensis) as the model system. In total, we recorded interactions for 31 foraging bumble bees and 6569 flower visitations. We found that decreasing soil moisture content correlated with decreasing size of all measured morphological traits except stamen length and nectar tube width. The reductions in floral size, petal width and length, nectar tube depth and number of flowers resulted in decreasing visitation rates by bumble bees. These decreasing visitations under lower soil moisture availability might be explained by lower numbers of flowers and thus a reduced attractiveness and/or by increased difficulties experienced by bumble bees in handling smaller flowers. Whether these effects act additively or synergistically on pollinator behaviour and whether this leads to changes in pollen transfer and to different selectionp ressures require further investigation.
Under dry conditions, plants can reduce their flower number and size to save water. Such changes, however may lead to reduced pollinator visitations as these traits play an important role in pollinator attraction. In this study, we explored how drought affects pollinator visitation via changes in floral traits. Therefore, we conducted a flight cage experiment with an automated visitation recording system observing bumblebee interactions with drought stressed and well-watered plants. Our results show that decreasing flower number and size under drought conditions resulted in decreasing bumblebee visits. This indicates that drought-stressed plants become less attractive for pollinators.
Exposure to radiation is a natural part of our environment. Yet, due to nuclear accidents such as at Chernobyl, some organisms are exposed to significantly elevated dose rates. Our understanding of ...the effects of radiation in the environment is limited, confounded by substantial interspecific differences in radio‐sensitivity and conflicting findings.
Here we study radiation impacts on bumblebees in the laboratory using principles from life‐history theory, which assume organismal investment in fitness‐related traits is constrained by resource availability and resource allocation decisions. To investigate how chronic radiation might negatively affect life‐history traits, we tested whether exposure affects bumblebee energy budgets by studying resource acquisition (feeding) and resource use (metabolic rate).
We monitored metabolic rate, movement and nectar intake of bumblebees before, during and after 10 days of radiation exposure. Subsequently, we monitored feeding and body mass across a dose rate gradient to investigate the dose rate threshold for these effects. We studied dose rates up to 200 μGy/hr: a range found today in some areas of the Chernobyl Exclusion Zone.
Chronic low‐dose radiation affected bumblebee energy budgets. At 200 μGy/hr nectar consumption elevated by 56% relative to controls, metabolic CO2 production increased by 18%, and time spent active rose by 30%. Once radiation exposure stopped, feeding remained elevated but CO2 production and activity returned to baseline. Our analysis indicates that elevated metabolic rate was not driven by increased activity but was instead closely associated with feeding increases. Our data suggest bumblebee nectar consumption was affected across the 50–200 μGy/hr range.
We show field‐realistic radiation exposure influences fundamental metabolic processes with potential to drive changes in many downstream life‐history traits. We hypothesise that radiation may trigger energetically costly repair mechanisms, increasing metabolic rate and nectar requirements. This change could have significant ecological consequences in contaminated landscapes, including Chernobyl. We demonstrate bumblebees are more sensitive to radiation than assumed by existing international frameworks for environmental radiological protection.
Read the free Plain Language Summary for this article on the Journal blog.
Read the free Plain Language Summary for this article on the Journal blog.
To counteract the decline of pollinators in Europe, conservation strategies traditionally focus on enhancing the local availability of semi‐natural habitats, as supported by the European Union's ...Common Agriculture Policy. In contrast, we show that densities of bumblebees, an important pollinator group in agroecosystems, were not determined by the proportion of semi‐natural habitats in agricultural landscapes. Instead, bumblebee densities were positively related to the availability of highly rewarding mass flowering crops (i.e. oilseed rape) in the landscape. In addition, mass flowering crops were only effective determinants of bumblebee densities when grown extensively at the landscape scale, but not at smaller local scales. Therefore, future conservation measures should consider the importance of mass flowering crops and the need for management schemes at landscape level to sustain vital pollination services in agroecosystems.
Recognition of the importance of bee conservation has grown in response to declines of managed honey bees and some wild bee species. Habitat loss has been implicated as a leading cause of declines, ...suggesting that ecological restoration is likely to play an increasing role in bee conservation efforts. In the midwestern United States, restoration of tallgrass prairie has traditionally targeted plant community objectives without explicit consideration for bees. However, restoration of prairie vegetation is likely to provide ancillary benefits to bees through increased foraging and nesting resources. We investigated community assembly of bees across a chronosequence of restored eastern tallgrass prairies and compared patterns to those in control and reference habitats (old fields and prairie remnants, respectively). We collected bees for 3 yr and measured diversity and abundance of in-bloom flowering plants, vegetation structure, ground cover, and surrounding land use as predictors of bee abundance and bee taxonomic and functional diversity. We found that site-level variables, but not site type or restoration age, were significant predictors of bee abundance (bloom diversity, P = 0.004; bare ground cover, P = 0.02) and bee diversity (bloom diversity, P = 0.01). There were significant correlations between overall composition of bee and blooming plant communities (Mantel test, P = 0.002), and both plant and bee assemblages in restorations were intermediate between those of old fields and remnant prairies. Restorations exhibited high bee beta diversity, i.e., restored sites' bee assemblages were taxonomically and functionally differentiated from each other. This pattern was strong in younger restorations (<20 yr old), but absent from older restorations (>20 yr), suggesting restored prairie bee communities become more similar to one another and more similar to remnant prairie bee communities over time with the arrival of more species and functional groups of bees. Our results indicate that old fields, restorations, and remnants provide habitat for diverse and abundant bee communities, but continued restoration of old fields will help support and conserve bee communities more similar to reference bee communities characteristic of remnant prairies.
Floral nectar represents an ephemeral habitat that is restricted in time and space to zoophilous flowering vegetation. To survive in these habitats, nectar-inhabiting microorganisms rely on animal ...vectors to disperse from one flower to the next. However, it remains unclear how nectar yeasts persist when flowers and nectar cease to be present. Here, we tested the hypothesis that hibernating bumblebee queens function as a reservoir for nectar yeasts in the absence of plants or pollinators during winter. Our results show that the nectar yeast, Metschnikowia reukaufii, was present in the gastrointestinal tract of wild bumblebee queens that emerged from hibernation and that it could persist inside the gut of hibernating queens under experimental conditions. However, no evidence for such persistence was found in the case of the second most frequent nectar yeast, M. gruessii. Furthermore, a phylloplane yeast that occasionally inhabits nectar, Rhodotorula mucilaginosa, was able to colonize the gut under experimental conditions. Two bumblebee-associated yeasts, Candida bombi and C. bombiphila, were successfully passed down generations after administration in commercial lab-reared bumblebees. Overall, these results demonstrate that bumblebees could act as a reservoir for nectar yeasts during winter when floral nectar is absent.
Managing farmland to benefit biodiversity is becoming increasingly necessary to combat biodiversity declines and maintain ecosystem services. Results‐based agri‐environmental schemes are a tool used ...to achieve this by paying farmers based on environmental results delivered. These schemes often utilise plant indicator species to assess results at field scale; however, it is unknown if focusing on enhancing a subset of one biodiversity group within results‐based schemes impacts wider biodiversity, and whether local‐scale implementation of results‐based schemes or/and the wider landscape are more important drivers of biodiversity patterns.
Insect pollinators provide important pollination services for many crop and wild plants, and as mobile organisms often experience landscape at large spatial scales. We tested whether insect pollinators are affected at local scale by a results‐based scheme scored based on plant indicators, or if landscape management is more important, and whether there were different responses between taxon‐specific groups. Bumblebees, solitary bees, hoverflies and butterflies were sampled using transects and pan traps in 23 fields with varying scores assigned by the scheme, situated in high‐intensity (≥65% improved grassland) or low‐intensity (≥65% semi‐natural grassland) landscapes.
Results indicate taxon‐specific responses to local and landscape management in semi‐natural grasslands. Bumblebees responded positively to local‐scale management in fields with higher floral diversity, whereas hoverflies and butterflies responded positively to low‐intensity landscape management.
Synthesis and applications. Using plant species as indicators for biodiversity in agri‐environment schemes can have indirect benefits for non‐target taxa like bumblebees, but broader indicators should be developed to incorporate other pollinator groups. Pollinator groups respond differently to local and landscape management in semi‐natural grasslands. Agri‐environmental management should consider a range of different management measures and landscape scale approaches where possible, to maximise benefits for a range of pollinator taxa.
Using plant species as indicators for biodiversity in agri‐environment schemes can have indirect benefits for non‐target taxa like bumblebees, but broader indicators should be developed to incorporate other pollinator groups. Pollinator groups respond differently to local and landscape management in semi‐natural grasslands. Agri‐environmental management should consider a range of different management measures and landscape scale approaches where possible, to maximise benefits for a range of pollinator taxa.
Microsporidia are intracellular parasites that have detrimental effects on their various invertebrate and vertebrate hosts. The microsporidia pathogenic to honeybees and bumblebees belong to the ...genus Vairimorpha (previously Nosema). Among these, V. bombi is the most widespread species worldwide and it infects a variety of bumblebee species. In this study, we investigated the infection of V. bombi among Japanese native bumblebees and the alien species, Bombus terrestris, established in Japan, using PCR and microscopy. We discovered that V. bombi infected the subgenus Bombus s. str. species/subspecies with a low prevalence in areas both with and without the presence of B. terrestris, suggesting that V. bombi may be native to Japan. In contrast, a newly discovered microsporidian parasite that is phylogenetically distinct from V. bombi was found to infect the subgenus Diversobombus species/subspecies with a high prevalence. Hence, if the new microsporidian species does not negatively affect the host and is vertically transmitted from queen to offspring, it may coexist with its host. In addition, this may suggest that V. bombi and the new microsporidium have different life history strategies. Microsporidia are spore-forming intracellular parasites of various invertebrates and vertebrates. Vairimorpha bombi negatively affects the fitness of bumblebees and its prevalence correlates with declining bumblebee populations. The invasive alien species Bombus terrestris colonized Japan and possibly introduced new parasites. To assess the infection prevalence of V. bombi in Japanese bumblebees and B. terrestris, we investigated V. bombi infections using PCR and microscopy. The prevalence of sporulating V. bombi infections in three Bombus s. str. species/subspecies was low, whereas that of non/low-sporulating Vairimorpha sp. infections in three Diversobombus species/subspecies was high. Invasive B. terrestris showed low prevalence of non/low-sporulating V. bombi infections and shared the same V. bombi haplotype with B. hypocrita found in Hokkaido, where B. terrestris is present, and in Honshu, where B. terrestris is absent. Although V. bombi may have been introduced with B. terrestris colonies imported from Europe, it seems to be originally distributed in Japan. Furthermore, a new Vairimorpha sp. was found in Japanese bumblebee species. V. bombi and Vairimorpha sp. showed different organ and host specificities in bumblebees. There are no reports on the specific effects of other Vairimorpha spp. on bumblebees; further studies are needed to clarify the individual characteristics of Vairimorpha spp.
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