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1. Edge effects and mating patterns in a bumblebee-pollinated plant

   https://doi.org/10.1093/aobpla/plaa033  

   Christopher, Dorothy A ; Mitchell, Randall J ; Trapnell, Dorset W ; Smallwood, Patrick A ; Semski, Wendy R ; Karron, Jeffrey D ( August 2020 , AoB PLANTS)

   Arceo-Gómez, Gerardo (Ed.)

   Abstract Researchers have long assumed that plant spatial location influences plant reproductive success and pollinator foraging behaviour. For example, many flowering plant populations have small, linear or irregular shapes that increase the proportion of plants on the edge, which may reduce mating opportunities through both male and female function. Additionally, plants that rely on pollinators may be particularly vulnerable to edge effects if those pollinators exhibit restricted foraging and pollen carryover is limited. To explore the effects of spatial location (edge vs. interior) on siring success, seed production, pollinator foraging patterns and pollen-mediated gene dispersal, we established a square experimental array of 49 Mimulus ringens (monkeyflower) plants. We observed foraging patterns of pollinating bumblebees and used paternity analysis to quantify male and female reproductive success and mate diversity for plants on the edge versus interior. We found no significant differences between edge and interior plants in the number of seeds sired, mothered or the number of sires per fruit. However, we found strong differences in pollinator behaviour based on plant location, including 15 % lower per flower visitation rates and substantially longer interplant moves for edge plants. This translated into 40 % greater pollen-mediated gene dispersal for edge than for interior plants. Overall, our results suggest that edge effects are not as strong as is commonly assumed, and that different plant reproduction parameters respond to spatial location independently. 

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2. Pollinator visitation rate and effectiveness vary with flowering phenology

   https://doi.org/10.1002/ajb2.1439  

   Gallagher, M. Kate ; Campbell, Diane R. ( February 2020 , American Journal of Botany)

   Flowering time may influence pollination success and seed set through a variety of mechanisms, including seasonal changes in total pollinator visitation or the composition and effectiveness of pollinator visitors.

   We investigated mechanisms by which changes in flowering phenology influence pollination and reproductive success ofMertensia ciliata(Boraginaceae). We manipulated flowering onset of potted plants and assessed the frequency and composition of pollinator visitors, as well as seed set. We tested whether floral visitors differed in their effectiveness as pollinators by measuring pollen receipt and seed set resulting from single visits to virgin flowers.

   Despite a five‐fold decrease in pollinator visitation over four weeks, we detected no significant difference in seed set among plants blooming at different times. On a per‐visit basis, each bumblebee transferred more conspecific pollen than did a solitary bee or a fly. The proportion of visits by bumblebees increased over the season, countering the decrease in visitation rate so that flowering time had little net effect on seed set.

   This work illustrates the need to consider pollinator effectiveness, along with changes in pollinator visitation and species composition to understand the mechanisms by which phenology affects levels of pollination.

    

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3. The individual and combined effects of snowmelt timing and frost exposure on the reproductive success of montane forbs

   https://doi.org/10.1111/1365-2745.13152  

   Pardee, Gabriella L. ; Jensen, Isaac O. ; Inouye, David W. ; Irwin, Rebecca E. ; Satake, ed., Akiko ( March 2019 , Journal of Ecology)

   Changes from historic weather patterns have affected the phenology of many organisms world‐wide. Altered phenology can introduce organisms to novel abiotic conditions during growth and modify species interactions, both of which could drive changes in reproduction.

   We explored how climate change can alter plant reproduction using an experiment in which we manipulated the individual and combined effects of snowmelt timing and frost exposure, and measured subsequent effects on flowering phenology, peak flower density, frost damage, pollinator visitation and reproduction of four subalpine wildflowers. Additionally, we conducted a pollen‐supplementation experiment to test whether the plants in our snowmelt and frost treatments were pollen limited for reproduction. The four plants included species flowering in early spring to mid‐summer.

   The phenology of all four species was significantly advanced, and the bloom duration was longer in the plots from which we removed snow, but with species‐specific responses to snow removal and frost exposure in terms of frost damage, flower production, pollinator visitation and reproduction. The two early blooming species showed significant signs of frost damage in both early snowmelt and frost treatments, which negatively impacted reproduction for one of the species. Further, we recorded fewer pollinators during flowering for the earliest‐blooming species in the snow removal plots. We also found lower fruit and seed set for the early blooming species in the snow removal treatment, which could be attributed to the plants growing under unfavourable abiotic conditions. However, the later‐blooming species escaped frost damage even in the plots where snow was removed, and experienced increased pollinator visitation and reproduction.

   Synthesis.This study provides insight into how plant communities could become altered due to changes in abiotic conditions, and some of the mechanisms involved. While early blooming species may be at a disadvantage under climate change, species that bloom later in the season may benefit from early snowmelt, suggesting that climate change has the potential to reshape flowering communities.

    

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4. Pollinator assemblage and pollen load differences on sympatric diploid and tetraploid cytotypes of the desert‐dominant Larrea tridentata

   https://doi.org/10.1002/ajb2.1605  

   Laport, Robert G. ; Minckley, Robert L. ; Pilson, Diana ( February 2021 , American Journal of Botany)

   Whole‐genome duplication (polyploidy) is an important force shaping flowering‐plant evolution. Ploidy‐specific plant–pollinator interactions represent important community‐level biotic interactions that can lead to nonrandom mating and the persistence of mixed‐ploidy populations.

   At a naturally occurring diploid–tetraploid contact zone of the autopolyploid desert shrubLarrea tridentata, we combined flower phenology analyses, collections of bees on plants of known cytotype, and flow cytometry analyses of bee‐collected pollen loads to investigate whether (1) diploid and tetraploid plants have unique bee pollinator assemblages, (2) bee taxa exhibit ploidy‐specific visitation and pollen collection biases, and (3) specialist and generalist bee taxa have ploidy‐specific visitation and pollen collection biases.

   Although bee assemblages overlapped, we found significant differences in bee visitation to co‐occurring diploids and tetraploids, with the introduced honeybee (Apis mellifera) and one native species (Andrenaspecies 12) more frequently visiting tetraploids. Consistent with bee assemblage differences, we found that diploid pollen was overrepresented among pollen loads on native bees, while pollen loads onA. melliferadid not deviate from the random expectation. However, mismatches between the ploidy of pollen loads and plants were common, consistent with ongoing intercytotype gene flow.

   Our data are consistent with cytotype‐specific bee visitation and suggest that pollinator behavior contributes to reduced diploid–tetraploid mating. Differences in bee visitation and pollen movement potentially contribute to an easing of minority cytotype exclusion and the facilitation of cytotype co‐occurrence.

    

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5. Experimental Test of the Combined Effects of Water Availability and Flowering Time on Pollinator Visitation and Seed Set

   https://doi.org/10.3389/fevo.2021.641693  

   Gallagher, M. Kate ; Campbell, Diane R. ( March 2021 , Frontiers in Ecology and Evolution)

   Climate change is likely to alter both flowering phenology and water availability for plants. Either of these changes alone can affect pollinator visitation and plant reproductive success. The relative impacts of phenology and water, and whether they interact in their impacts on plant reproductive success remain, however, largely unexplored. We manipulated flowering phenology and soil moisture in a factorial experiment with the subalpine perennial Mertensia ciliata (Boraginaceae). We examined responses of floral traits, floral abundance, pollinator visitation, and composition of visits by bumblebees vs. other pollinators. To determine the net effects on plant reproductive success, we also measured seed production and seed mass. Reduced water led to shorter, narrower flowers that produced less nectar. Late flowering plants produced fewer and shorter flowers. Both flowering phenology and water availability influenced pollination and reproductive success. Differences in flowering phenology had greater effects on pollinator visitation than did changes in water availability, but the reverse was true for seed production and mass, which were enhanced by greater water availability. The probability of receiving a flower visit declined over the season, coinciding with a decline in floral abundance in the arrays. Among plants receiving visits, both the visitation rate and percent of non-bumblebee visitors declined after the first week and remained low until the final week. We detected interactions of phenology and water on pollinator visitor composition, in which plants subject to drought were the only group to experience a late-season resurgence in visits by solitary bees and flies. Despite that interaction, net reproductive success measured as seed production responded additively to the two manipulations of water and phenology. Commonly observed declines in flower size and reward due to drought or shifts in phenology may not necessarily result in reduced plant reproductive success, which in M. ciliata responded more directly to water availability. The results highlight the need to go beyond studying single responses to climate changes, such as either phenology of a single species or how it experiences an abiotic factor, in order to understand how climate change may affect plant reproductive success. 

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