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Rockow DJ, Martel C, Arceo‐Gómez G. Differential impacts of land-use change on multiple components of common milkweed ( Asclepias syriaca) pollination success. Ecol Evol 2024; 14:e11494. [PMID: 38855315 PMCID: PMC11156956 DOI: 10.1002/ece3.11494] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2024] [Revised: 05/07/2024] [Accepted: 05/13/2024] [Indexed: 06/11/2024] Open
Abstract
Land-use change is one the greatest threats to biodiversity and is projected to increase in magnitude in the coming years, stressing the importance of better understanding how land-use change may affect vital ecosystem services, such as pollination. Past studies on the impact of land-use change have largely focused on only one aspect of the pollination process (e.g., pollinator composition, pollinator visitation, and pollen transfer), potentially misrepresenting the full complexity of land-use effects on pollination services. Evaluating the impacts across multiple components of the pollination process can also help pinpoint the underlying mechanisms driving land-use change effects. This study evaluates how land-use change affects multiple aspects of the pollination process in common milkweed populations, including pollinator community composition, pollinator visitation rate, pollen removal, and pollen deposition. Overall, land-use change altered floral visitor composition, with small bees having a larger presence in developed areas. Insect visitation rate and pollen removal were also higher in more developed areas, perhaps suggesting a positive impact of land-use change. However, pollen deposition did not differ between developed and undeveloped sites. Our findings highlight the complexity evaluating land-use change effects on pollination, as these likely depend on the specific aspect of pollination evaluated and on the of the intensity of disturbance. Our study stresses the importance of evaluating multiple components of the pollination process in order to fully understand overall effects and mechanisms underlying land-use change effects on this vital ecosystem service.
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Affiliation(s)
- David J. Rockow
- Department of Biological SciencesEast Tennessee State UniversityJohnson CityTennesseeUSA
| | - Carlos Martel
- Department of Biological SciencesEast Tennessee State UniversityJohnson CityTennesseeUSA
- Royal Botanic Gardens, KewRichmondUK
| | - Gerardo Arceo‐Gómez
- Department of Biological SciencesEast Tennessee State UniversityJohnson CityTennesseeUSA
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2
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Waterman R, Sahli H, Koelling VA, Karoly K, Conner JK. Strong evidence for positive and negative correlational selection revealed by recreating ancestral variation. Evolution 2023; 77:264-275. [PMID: 36622224 DOI: 10.1093/evolut/qpac001] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Revised: 09/27/2022] [Accepted: 10/06/2022] [Indexed: 01/10/2023]
Abstract
The study of adaptation helps explain biodiversity and predict future evolution. Yet the process of adaptation can be difficult to observe due to limited phenotypic variation in contemporary populations. Furthermore, the scarcity of male fitness estimates has made it difficult to both understand adaptation and evaluate sexual conflict hypotheses. We addressed both issues in our study of two anther position traits in wild radish (Raphanus raphanistrum): anther exsertion (long filament - corolla tube lengths) and anther separation (long - short filament lengths). These traits affect pollination efficiency and are particularly interesting due to the unusually high correlations among their component traits. We measured selection through male and female fitness on wild radish plants from populations artificially selected to recreate ancestral variation in each anther trait. We found little evidence for conflicts between male and female function. We found strong evidence for stabilizing selection on anther exsertion and disruptive selection on anther separation, indicating positive and negative correlational selection on the component traits. Intermediate levels of exsertion are likely an adaptation to best contact small bees. The function of anther separation is less clear, but future studies might investigate pollen placement on pollinators and compare species possessing multiple stamen types.
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Affiliation(s)
- Robin Waterman
- Kellogg Biological Station and Department of Plant Biology, Michigan State University, Hickory Corners, MI, United States
| | - Heather Sahli
- Kellogg Biological Station and Department of Plant Biology, Michigan State University, Hickory Corners, MI, United States.,Department of Biology, Shippensburg University, Shippensburg, PA 17257, United States
| | - Vanessa A Koelling
- Biology Department, Reed College, Portland, OR, United States.,Current Address: Department of Biology and Environmental Science, Auburn University at Montgomery, Montgomery, AL, United States
| | - Keith Karoly
- Biology Department, Reed College, Portland, OR, United States
| | - Jeffrey K Conner
- Kellogg Biological Station and Department of Plant Biology, Michigan State University, Hickory Corners, MI, United States
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3
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Rodríguez-Otero C, Hedrén M, Friberg M, Opedal ØH. Analysis of trait-performance-fitness relationships reveals pollinator-mediated selection on orchid pollination traits. AMERICAN JOURNAL OF BOTANY 2023:e16128. [PMID: 36655508 DOI: 10.1002/ajb2.16128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Revised: 07/24/2022] [Accepted: 08/01/2022] [Indexed: 06/17/2023]
Abstract
PREMISE The role of pollinators in evolutionary floral divergence has spurred substantial effort into measuring pollinator-mediated phenotypic selection and its variation in space and time. For such estimates, the fitness consequences of pollination processes must be separated from other factors affecting fitness. METHODS We built a fitness function linking phenotypic traits of food-deceptive orchids to female reproductive success by including pollinator visitation and pollen deposition as intermediate performance components and used the fitness function to estimate the strength of pollinator-mediated selection through female reproductive success. We also quantified male performance as pollinarium removal and assessed similarity in trait effects on male and female performance. RESULTS The proportion of plants visited at least once by an effective pollinator was moderate to high, ranging from 53.7% to 85.1%. Tall, many-flowered plants were often more likely to be visited and pollinated. Given effective pollination, pollen deposition onto stigmas tended to be more likely for taller plants. Pollen deposition further depended on traits affecting the physical fit of pollinators to flowers (flower size, spur length), though the exact relationships varied in time and space. Using the fitness function to assess pollinator-mediated selection through female reproductive success acting on multiple traits, we found that selection varied detectably among taxa after accounting for sampling uncertainty. Across taxa, selection on most traits was stronger on average and more variable when pollination was less reliable. CONCLUSIONS These results support pollination-related trait-performance-fitness relationships and thus pollinator-mediated selection on traits functionally involved in the pollination process.
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Affiliation(s)
| | - Mikael Hedrén
- Department of Biology, Biodiversity Unit, Lund University, SE, 22362, Lund, Sweden
| | - Magne Friberg
- Department of Biology, Biodiversity Unit, Lund University, SE, 22362, Lund, Sweden
| | - Øystein H Opedal
- Department of Biology, Biodiversity Unit, Lund University, SE, 22362, Lund, Sweden
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4
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Herbivory, plant traits and nectar chemistry interact to affect the community of insect visitors and pollination in common milkweed, Asclepias syriaca. Oecologia 2023; 201:91-105. [PMID: 36456875 DOI: 10.1007/s00442-022-05290-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Accepted: 11/07/2022] [Indexed: 12/04/2022]
Abstract
Herbivory can alter plant fitness directly through changing reproductive allocation and indirectly through changing pollinator identity or behavior. Common milkweed is a plant of conservation concern with an inducible chemical defense that is also an important nectar resource. In this study, we aim to understand how herbivory severity and plant traits, including morphology and nectar chemistry, interact to affect insect visitation and pod production in common milkweed. We conducted pollinator watches on plants with experimentally varied herbivory severity and quantified insect frequency and visit length as a response to nectar chemistry, ramet height, number of inflorescences, number of flowers per inflorescence and percent tissue removed. We also quantified pollinator effectiveness and importance. Increased herbivory severity reduced floral displays, including fewer inflorescences and fewer flowers per inflorescence. A reduced floral display was correlated with reduced sucrose, fructose and glucose and resulted in a reduced number and species richness of insect visitors. Fewer flowers per inflorescence reduced the frequency of bumble bee and fly visitors, which were two important pollinators. Although honeybees, flies, small bees, soldier beetles and bumble bees were equally effective pollinators, only bumble bee frequency was positively correlated with pod production. The differences in pollinator visitation have the potential to create diversifying selection on plant floral traits, many of which are also affected by herbivores. This research demonstrates potentially conflicting selection pressures between native and non-native pollinators as well as non-native herbivores.
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5
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Wu Y, Barrett SCH, Duan X, Zhang J, Cha Y, Tu C, Li Q. Herbivore-Mediated Selection on Floral Display Covaries Nonlinearly With Plant-Antagonistic Interaction Intensity Among Primrose Populations. FRONTIERS IN PLANT SCIENCE 2021; 12:727957. [PMID: 34868113 PMCID: PMC8636000 DOI: 10.3389/fpls.2021.727957] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/20/2021] [Accepted: 10/22/2021] [Indexed: 06/13/2023]
Abstract
Quantifying the relations between plant-antagonistic interactions and natural selection among populations is important for predicting how spatial variation in ecological interactions drive adaptive differentiation. Here, we investigate the relations between the opportunity for selection, herbivore-mediated selection, and the intensity of plant-herbivore interaction among 11 populations of the insect-pollinated plant Primula florindae over 2 years. We experimentally quantified herbivore-mediated directional selection on three floral traits (two display and one phenological) within populations and found evidence for herbivore-mediated selection for a later flowering start date and a greater number of flowers per plant. The opportunity for selection and strength of herbivore-mediated selection on number of flowers varied nonlinearly with the intensity of herbivory among populations. These parameters increased and then decreased with increasing intensity of plant-herbivore interactions, defined as an increase in the ratio of herbivore-damaged flowers per individual. Our results provide novel insights into how plant-antagonistic interactions can shape spatial variation in selection on floral traits and contribute toward understanding the mechanistic basis of geographic variation in angiosperm flowers.
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Affiliation(s)
- Yun Wu
- School of Civil Engineering, Architecture and Environment, Xihua University, Chengdu, China
- Yunnan Key Laboratory of Plant Reproductive Adaptation and Evolutionary Ecology, Yunnan University, Kunming, China
- Laboratory of Ecology and Evolutionary Biology, School of Ecology and Environmental Science, Yunnan University, Kunming, China
| | - Spencer C. H. Barrett
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | - Xuyu Duan
- College of Landscape Architecture, Sichuan Agricultural University, Chengdu, China
| | - Jie Zhang
- Yunnan Key Laboratory of Plant Reproductive Adaptation and Evolutionary Ecology, Yunnan University, Kunming, China
- Laboratory of Ecology and Evolutionary Biology, School of Ecology and Environmental Science, Yunnan University, Kunming, China
| | - Yongpeng Cha
- Yunnan Key Laboratory of Plant Reproductive Adaptation and Evolutionary Ecology, Yunnan University, Kunming, China
- Laboratory of Ecology and Evolutionary Biology, School of Ecology and Environmental Science, Yunnan University, Kunming, China
| | - Chengyi Tu
- Yunnan Key Laboratory of Plant Reproductive Adaptation and Evolutionary Ecology, Yunnan University, Kunming, China
- Laboratory of Ecology and Evolutionary Biology, School of Ecology and Environmental Science, Yunnan University, Kunming, China
| | - Qingjun Li
- Yunnan Key Laboratory of Plant Reproductive Adaptation and Evolutionary Ecology, Yunnan University, Kunming, China
- Laboratory of Ecology and Evolutionary Biology, School of Ecology and Environmental Science, Yunnan University, Kunming, China
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6
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Benoit AD, Caruso CM. A sit-and-wait predator, but not an active-pursuit predator, alters pollinator-mediated selection on floral traits. Ecology 2021; 102:e03506. [PMID: 34319595 DOI: 10.1002/ecy.3506] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Revised: 05/12/2021] [Accepted: 05/25/2021] [Indexed: 12/27/2022]
Abstract
Indirect species interactions are ubiquitous in nature, often outnumbering direct species interactions. Yet despite evidence that indirect interactions have strong ecological effects, relatively little is known about whether they can shape adaptive evolution by altering the strength and/or direction of natural selection. We tested whether indirect interactions affect the strength and direction of pollinator-mediated selection on floral traits of the bumble-bee pollinated wildflower Lobelia siphilitica. We estimated the indirect effects of two pollinator predators with contrasting hunting modes: dragonflies (Aeshnidae and Corduliidae) and ambush bugs (Phymata americana, Reduviidae). Because dragonflies are active pursuit predators, we hypothesized that they would strengthen pollinator-mediated selection by weakening plant-pollinator interactions (i.e., a density-mediated indirect effect). In contrast, because ambush bugs are sit-and-wait predators, we hypothesized that they would weaken or reverse the direction of pollinator-mediated selection by altering pollinator foraging behavior (i.e., a trait-mediated indirect effect). Specifically, if ambush bugs hunt from plants with traits that attract pollinators (i.e., prey), then pollinators will spend less time visiting those plants, weakening or reversing the direction of selection on attractive floral traits. We did not find evidence that high dragonfly abundance strengthened selection on floral traits via a density-mediated indirect effect: neither pollen limitation (a proxy for the strength of plant-pollinator interactions) nor directional selection on floral traits of L. siphilitica differed significantly between high- and low-dragonfly abundance treatments. In contrast, we did find evidence that ambush bug presence affected selection on floral traits via a trait-mediated indirect effect: ambush bugs hunted from L. siphilitica plants with larger daily floral displays, reversing the direction of pollinator-mediated selection on daily display size. These results suggest that indirect species interactions have the potential to shape adaptive evolution by altering natural selection.
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Affiliation(s)
- Amanda D Benoit
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada
| | - Christina M Caruso
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada
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7
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Zhou J, Reynolds RJ, Zimmer EA, Dudash MR, Fenster CB. Variable and sexually conflicting selection on
Silene stellata
floral traits by a putative moth pollinator selective agent. Evolution 2020; 74:1321-1334. [DOI: 10.1111/evo.13965] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2019] [Revised: 02/21/2020] [Accepted: 03/13/2020] [Indexed: 10/24/2022]
Affiliation(s)
- Juannan Zhou
- Simons Center for Quantitative Biology Cold Spring Harbor Laboratory Cold Spring Harbor NY 11724 USA
| | - Richard J. Reynolds
- Division of Clinical Immunology and Rheumatology, Department of Medicine University of Alabama at Birmingham Birmingham AL 35294 USA
| | - Elizabeth A. Zimmer
- Department of Botany National Museum of Natural History, MRC 166 Smithsonian Institution Washington DC 20013–7012 USA
| | - Michele R. Dudash
- Department of Natural Resource Management South Dakota State University Brookings SD 57007 USA
| | - Charles B. Fenster
- Department of Biology and Microbiology South Dakota State University Brookings SD 57007 USA
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8
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Flower traits associated with the visitation patterns of bees. Oecologia 2020; 193:511-522. [PMID: 32495034 DOI: 10.1007/s00442-020-04674-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Accepted: 05/26/2020] [Indexed: 10/24/2022]
Abstract
Plant-pollinator interactions are partially driven by the expression of plant traits that signal and attract bees to the nutritional resources within flowers. Although multiple physical and chemical floral traits are known to influence the visitation patterns of bees, how distinct bee groups vary in their responses to floral traits has yet to be elucidated. In this study, we used a common garden experiment to test for morphological floral traits associated with pollen quantity at the plant species level, and examined how the visitation patterns of taxonomically and functionally distinct bee groups are related to flower trait characteristics of 39 wildflower species. We also determined how floral traits influence the structure of wild bee communities visiting plants and whether this varies among geographic localities. Our results suggest that floral area is the primary morphological floral trait related to bee visitation of several distinct bee groups, but that wild bee families and functionally distinct bee groups have unique responses to floral trait expression. The composition of the wild bee communities visiting different plants was most strongly associated with variability in floral area, flower height, and the quantity of pollen retained in flowers. Our results inform wildflower habitat management for bees by demonstrating that the visitation patterns of distinct bee taxa can be predicted by floral traits, and highlight that variability in these traits should be considered when selecting plants to support pollinators.
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9
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Weitemier K, Straub SC, Fishbein M, Bailey CD, Cronn RC, Liston A. A draft genome and transcriptome of common milkweed ( Asclepias syriaca) as resources for evolutionary, ecological, and molecular studies in milkweeds and Apocynaceae. PeerJ 2019; 7:e7649. [PMID: 31579586 PMCID: PMC6756140 DOI: 10.7717/peerj.7649] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Accepted: 08/09/2019] [Indexed: 02/06/2023] Open
Abstract
Milkweeds (Asclepias) are used in wide-ranging studies including floral development, pollination biology, plant-insect interactions and co-evolution, secondary metabolite chemistry, and rapid diversification. We present a transcriptome and draft nuclear genome assembly of the common milkweed, Asclepias syriaca. This reconstruction of the nuclear genome is augmented by linkage group information, adding to existing chloroplast and mitochondrial genomic resources for this member of the Apocynaceae subfamily Asclepiadoideae. The genome was sequenced to 80.4× depth and the draft assembly contains 54,266 scaffolds ≥1 kbp, with N50 = 3,415 bp, representing 37% (156.6 Mbp) of the estimated 420 Mbp genome. A total of 14,474 protein-coding genes were identified based on transcript evidence, closely related proteins, and ab initio models, and 95% of genes were annotated. A large proportion of gene space is represented in the assembly, with 96.7% of Asclepias transcripts, 88.4% of transcripts from the related genus Calotropis, and 90.6% of proteins from Coffea mapping to the assembly. Scaffolds covering 75 Mbp of the Asclepias assembly formed 11 linkage groups. Comparisons of these groups with pseudochromosomes in Coffea found that six chromosomes show consistent stability in gene content, while one may have a long history of fragmentation and rearrangement. The progesterone 5β-reductase gene family, a key component of cardenolide production, is likely reduced in Asclepias relative to other Apocynaceae. The genome and transcriptome of common milkweed provide a rich resource for future studies of the ecology and evolution of a charismatic plant family.
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Affiliation(s)
- Kevin Weitemier
- Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR, USA
| | | | - Mark Fishbein
- Department of Plant Biology, Ecology, and Evolution, Oklahoma State University, Stillwater, OK, USA
| | - C. Donovan Bailey
- Department of Biology, New Mexico State University, Las Cruces, NM, USA
| | - Richard C. Cronn
- Pacific Northwest Research Station, USDA Forest Service, Corvallis, OR, USA
| | - Aaron Liston
- Department of Botany & Plant Pathology, Oregon State University, Corvallis, OR, USA
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10
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Smith SD, Kriebel R. Convergent evolution of floral shape tied to pollinator shifts in Iochrominae (Solanaceae)*. Evolution 2018; 72:688-697. [DOI: 10.1111/evo.13416] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Revised: 12/01/2017] [Accepted: 12/08/2017] [Indexed: 12/31/2022]
Affiliation(s)
- Stacey D. Smith
- Department of Ecology and Evolutionary Biology University of Colorado Boulder Colorado 80305
| | - Ricardo Kriebel
- Department of Botany University of Wisconsin – Madison Madison Wisconsin 53706
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11
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Ramos BDCM, Rodríguez-Gironés MA, Rodrigues D. Learning in two butterfly species when using flowers of the tropical milkweed Asclepias curassavica: No benefits for pollination. AMERICAN JOURNAL OF BOTANY 2017; 104:1168-1178. [PMID: 28790090 DOI: 10.3732/ajb.1700040] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Accepted: 06/16/2017] [Indexed: 06/07/2023]
Abstract
PREMISE OF THE STUDY The ability of insect visitors to learn to manipulate complex flowers has important consequences for foraging efficiency and plant fitness. We investigated learning by two butterfly species, Danaus erippus and Heliconius erato, as they foraged on the complex flowers of Asclepias curassavica, as well as the consequences for pollination. METHODS To examine learning with respect to flower manipulation, butterflies were individually tested during four consecutive days under insectary conditions. At the end of each test, we recorded the number of pollinaria attached to the body of each butterfly and scored visited flowers for numbers of removed and inserted pollinia. We also conducted a field study to survey D. erippus and H. erato visiting flowers of A. curassavica, as well as to record numbers of pollinaria attached to the butterflies' bodies, and surveyed A. curassavica plants in the field to inspect flowers for pollinium removal and insertion. KEY RESULTS Learning improves the ability of both butterfly species to avoid the nonrewarding flower parts and to locate nectar more efficiently. There were no experience effects, for either species, on the numbers of removed and inserted pollinia. Heliconius erato removed and inserted more pollinia than D. erippus. For both butterfly species, pollinium removal was higher than pollinium insertion. CONCLUSION This study is the first to show that Danaus and Heliconius butterflies can learn to manipulate complex flowers, but this learning ability does not confer benefits to pollination in A. curassavica.
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Affiliation(s)
- Bruna de Cássia Menezes Ramos
- Laboratório de Interações Inseto-Planta, Programa de Pós-Graduação em Ecologia, Instituto de Biologia, Universidade Federal do Rio de Janeiro, P.O. Box 68020, 21.941-902 Cidade Universitária, Ilha do Fundão, Rio de Janeiro, RJ, Brazil
| | - Miguel Angel Rodríguez-Gironés
- Department of Functional and Evolutionary Ecology, Estación Experimental de Zonas Áridas (EEZA/CSIC), Ctra. de Sacramento S/N, La Cañada de San Urbano, 04120 Almería, Spain
| | - Daniela Rodrigues
- Laboratório de Interações Inseto-Planta, Programa de Pós-Graduação em Ecologia, Instituto de Biologia, Universidade Federal do Rio de Janeiro, P.O. Box 68020, 21.941-902 Cidade Universitária, Ilha do Fundão, Rio de Janeiro, RJ, Brazil
- Departamento de Ecologia, Instituto de Biologia, Universidade Federal do Rio de Janeiro, P.O. Box 68020, 21.941-902 Cidade Universitária, Ilha do Fundão, Rio de Janeiro, RJ, Brazil
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12
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La Rosa RJ, Conner JK. Floral function: effects of traits on pollinators, male and female pollination success, and female fitness across three species of milkweeds (Asclepias). AMERICAN JOURNAL OF BOTANY 2017; 104:150-160. [PMID: 28104591 DOI: 10.3732/ajb.1600328] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2016] [Accepted: 12/19/2016] [Indexed: 06/06/2023]
Abstract
PREMISE OF THE STUDY Central questions in plant reproductive ecology are whether the functions of floral traits in hermaphrodites create conflict between sexes that could slow evolution, and whether individual floral traits function in pollinator attraction, efficiency, or both. We studied how floral traits affect pollinator visitation and efficiency, and how they affect male and female function and female fitness within and across three Asclepias species that differ in floral morphology. METHODS Using separate multiple regressions, we regressed pollen removal, deposition, and fruit number onto six floral traits. We also used path analyses integrating these variables with pollinator visitation data for two of the species to further explore floral function and its effects on fruit production. KEY RESULTS Most traits affected male pollination success only, and these effects often differed between species. The exception was increased slit length, which increased pollinia insertion in two of the species. There were no interspecific differences in the effects of the traits on female pollination success. All traits except horn reach affected pollination efficiency in at least one species, and horn reach and two hood dimensions were the only traits to affect pollinator attraction, but in just one species. CONCLUSIONS Traits tended to function in only one sex, and more traits affected function through pollinator efficiency than through attraction. There was no significant link between female pollination success and female fitness in any of the three species; this pattern is consistent with fruit production not being limited by pollen deposition.
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Affiliation(s)
- Raffica J La Rosa
- W. K. Kellogg Biological Station, Department of Plant Biology, and Program in Ecology, Evolutionary Biology and Behavior, Michigan State University, 3700 E. Gull Lake Dr., Hickory Corners, Michigan 49060
| | - Jeffrey K Conner
- W. K. Kellogg Biological Station, Department of Plant Biology, and Program in Ecology, Evolutionary Biology and Behavior, Michigan State University, 3700 E. Gull Lake Dr., Hickory Corners, Michigan 49060
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