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1. A key floral scent component (β‐trans‐bergamotene) drives pollinator preferences independently of pollen rewards in seep monkeyflower

   https://doi.org/10.1111/1365-2435.13246  

   Haber, Ariela I. ; Sims, James W. ; Mescher, Mark C. ; De Moraes, Consuelo M. ; Carr, David E. ; Brody, ed., Alison ( December 2018 , Functional Ecology)

   Floral odours play an important role in attracting insect pollinators. Because pollinators visit flowers to obtain pollen and nectar rewards, they should prefer floral odour profiles associated with the highest‐rewarding flowers (honest signals). In previous work, bumblebees exhibited a preference for flowers from outbred over inbredMimulus guttatusplants. Pollen is the only floral reward inM. guttatus, and pollen viability (a reliable indicator of protein content) is reduced in inbred plants. Yet, differences in pollen viability did not explain the observed preferences.

   In this study, we examined the floral volatile profiles of inbred and outbredM. guttatusto identify inbreeding effects and associations between volatile compounds and the number of viable pollen grains per flower, designated “PRQ” (pollen reward quality). We also conducted pairwise choice tests withBombus impatiensto evaluate the ability of bees to discriminate between odours of rewarding and non‐rewarding flowers and to determine whether bumblebee preferences are explained by differences in the floral odours of inbred and outbred plants.

   Inbred plants exhibited reduced emission of β‐trans‐bergamotene, the second‐most abundant compound in the volatile blend of outbred plants. Furthermore, pollen and fertile anthers emitted nonadecane. Six other compounds in the floral blend were positively correlated withPRQ. There was no overlap between compounds affected by inbreeding and compounds associated withPRQ.

   Even when given prior experience foraging onM. guttatus, bumblebees did not distinguish between the floral odours of rewarding and non‐rewarding outbred plants. However, they preferred floral odours from non‐rewarding outbred plants over rewarding inbred plants. Bumblebees without prior experience of flowers preferred volatile blends with higher versus lower amounts of β‐trans‐bergamotene.

   Taken together, these results suggest that the volatile emissions ofM. guttatusprovide reliable indicators of pollen rewards (potential honest signals), but that the preference of bumblebees for outbred plants is not driven by these cues but rather by a sensory bias for β‐trans‐bergamotene. This may represent a subtle form of deceit‐pollination that allows plants to attract pollinators while minimizing investment in costly rewards.

   Aplain language summaryis available for this article.

    

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2. Honest floral signalling traits vary across and within populations in an insect‐pollinated plant

   https://doi.org/10.1111/1365-2435.14405  

   Eisen, Katherine E. ; Boutsi, Sotiria ; Halley, John M. ; Pace, Loretta ; Petrén, Hampus ; Thosteman, Hanna ; Friberg, Magne ( July 2023 , Functional Ecology)

   In flowering plants that produce concealed rewards, pollinator foraging preferences may select for floral advertisement traits that are correlated with rewards. To date, studies have not focused on the potential for honest signals to vary across populations, which could occur due to differences in pollinator communities or plant mating system.

   We tested for variation in honest signals across and within populations and mating systems inArabis alpina, a broadly distributed arctic‐alpine perennial herb that is visited by a variable community of insects. In a greenhouse common garden, we tested for correlations between corolla area, floral scent and nectar volume in 29 populations. In 12 field populations, we examined variation in pollen limitation and corolla area.

   Across and within populations and mating systems, larger flowers generally produced more nectar. Total scent emission was not correlated with nectar production, but two compounds—phenylacetaldehyde and benzyl alcohol—may be honest signals in some populations. Corolla area was correlated with pollen limitation only across populations.

   Our results suggest that honest signals may be similar across populations but may not result from contemporary direct selection on floral advertisements.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

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3. The dispersal of microbes among and within flowers by butterflies

   https://doi.org/10.1111/een.13239  

   Olson, Malia M. ; Ravikanthachari, Nitin ; Blackwell, Meredith ; Boggs, Carol L. ( March 2023 , Ecological Entomology)

   Floral microbes, including bacteria and fungi, alter nectar quality, thus changing pollinator visitation. Conversely, pollinator visitation can change the floral microbial community.

   Most studies on dispersal of floral microbes have focused on bees, ants or hummingbirds, yet Lepidoptera are important pollinators.

   We asked (a) where are microbes present on the butterfly body, (b) do butterflies transfer microbes while foraging, and (c) how does butterfly foraging affect microbial abundance on different floret structures.

   The tarsi and proboscis had significantly more microbes than the thorax in wild‐caughtGlaucopsyche lygdamus(Lepidoptera: Lycaenidae) andSpeyeria mormonia(Lepidoptera: Nymphalidae).Glaucopsyche lygdamus, a smaller‐bodied species, had fewer microbes thanS. mormonia.

   As a marker for microbes, we used a bacterium (Rhodococcus fascians,near NCBI Y11196) isolated from aS. mormoniathat was foraging for nectar, and examined its dispersal byG. lygdamusandS. mormoniavisiting florets ofPyrrocoma crocea(Asteraceae). Microbial dispersal among florets correlated positively with bacterial abundance in the donor floret. Dispersal also depended on butterfly species, age, and bacterial load carried by the butterfly.

   Recipient florets had less bacteria than donor florets. The nectaries had more bacteria than the anthers or the stigmas, while anthers and stigmas did not differ from each other. There was no differential transmission among floral organs.

   Lepidoptera thus act as vectors of floral microbes. Including Lepidoptera is thus crucial to an understanding of plant–pollinator–microbe interactions. Future studies should consider the role of vectored microbes in lepidopteran ecology and fitness.

    

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4. Flowering resources distract pollinators from crops: Model predictions from landscape simulations

   https://doi.org/10.1111/1365-2664.13333  

   Nicholson, Charlie C. ; Ricketts, Taylor H. ; Koh, Insu ; Smith, Henrik G. ; Lonsdorf, Eric V. ; Olsson, Ola ; Requier, ed., Fabrice ( February 2019 , Journal of Applied Ecology)

   Enhancing floral resources is a widely accepted strategy for supporting wild bees and promoting crop pollination. Planning effective enhancements can be informed with pollination service models, but these models should capture the behavioural and spatial dynamics of service‐providing organisms. Model predictions, and hence management recommendations, are likely to be sensitive to these dynamics.

   We used two established models of pollinator foraging to investigate whether habitat enhancement improves crop visitation; whether this effect is influenced by pollinator foraging distance and landscape pattern; and whether behavioural detail improves model predictions.

   The more detailed central place foraging model better predicted variation in bee visitation observed between habitat types, because it includes optimized trade‐offs between patch quality and distance. Both models performed well when predicting visitation rates across broader scales.

   Using real agricultural landscapes and simulating habitat enhancements, we show that additional floral resources can have diverging effects on predicted crop visitation. When only co‐flowering resources were added, optimally foraging bees concentrated in enhancements to the detriment of crop pollination. For both models, adding nesting resources increased crop visitation. Finally, the marginal effect of enhancements was greater in simple landscapes.

   Synthesis and applications. Model results help to identify the conditions under which habitat enhancements are most likely to increase pollination services in agriculture. Three design principles for pollinator habitat enhancement emerge: (a) enhancing only flowers can diminish services by distracting pollinators away from crops, (b) providing nesting resources is more likely to increase bee populations and crop visitation and (c) the benefit of enhancements will be greatest in landscapes that do not already contain abundant habitat.

    

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5. Evidence of exploitative competition between honey bees and native bees in two California landscapes

   https://doi.org/10.1111/1365-2656.13973  

   Page, Maureen L. ; Williams, Neal M. ( June 2023 , Journal of Animal Ecology)

   Human‐mediated species introductions provide real‐time experiments in how communities respond to interspecific competition. For example, managed honey beesApis mellifera(L.) have been widely introduced outside their native range and may compete with native bees for pollen and nectar. Indeed, multiple studies suggest that honey bees and native bees overlap in their use of floral resources. However, for resource overlap to negatively impact resource collection by native bees, resource availability must also decline, and few studies investigate impacts of honey bee competition on native bee floral visits and floral resource availability simultaneously.

   In this study, we investigate impacts of increasing honey bee abundance on native bee visitation patterns, pollen diets, and nectar and pollen resource availability in two Californian landscapes: wildflower plantings in the Central Valley and montane meadows in the Sierra.

   We collected data on bee visits to flowers, pollen and nectar availability, and pollen carried on bee bodies across multiple sites in the Sierra and Central Valley. We then constructed plant‐pollinator visitation networks to assess how increasing honey bee abundance impacted perceived apparent competition (PAC), a measure of niche overlap, and pollinator specialization (d'). We also compared PAC values against null expectations to address whether observed changes in niche overlap were greater or less than what we would expect given the relative abundances of interacting partners.

   We find clear evidence of exploitative competition in both ecosystems based on the following results: (1) honey bee competition increased niche overlap between honey bees and native bees, (2) increased honey bee abundance led to decreased pollen and nectar availability in flowers, and (3) native bee communities responded to competition by shifting their floral visits, with some becoming more specialized and others becoming more generalized depending on the ecosystem and bee taxon considered.

   Although native bees can adapt to honey bee competition by shifting their floral visits, the coexistence of honey bees and native bees is tenuous and will depend on floral resource availability. Preserving and augmenting floral resources is therefore essential in mitigating negative impacts of honey bee competition. In two California ecosystems, honey bee competition decreases pollen and nectar resource availability in flowers and alters native bee diets with potential implications for bee conservation and wildlands management.

    

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