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Stewart AB, Diller C, Dudash MR, Fenster CB. Pollination-precision hypothesis: support from native honey bees and nectar bats. THE NEW PHYTOLOGIST 2022; 235:1629-1640. [PMID: 35194792 DOI: 10.1111/nph.18050] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Accepted: 02/09/2022] [Indexed: 05/28/2023]
Abstract
The evolution of floral traits is often considered to reflect selection for increased pollination efficiency. Known as the pollination-precision hypothesis, increased pollination efficiency is achieved by enhancing pollen deposition on precise areas of the pollinator. Most research to date addressing this hypothesis has examined plant species that are a priori predicted to place pollen precisely, but we still lack comparisons with species predicted to have low pollination efficiency. We studied 39 plant species with diverse floral morphologies and measured the precision of pollen placement on two pollinator groups: honey bees (genus Apis) and nectar bats (family Pteropodidae). Pollen was collected from four locations of each pollinator's body (bees: dorsal thorax, ventral thorax, dorsal abdomen, ventral abdomen; bats: crown, face, chest, wing) to calculate pollen placement precision using Pielou's evenness index. We also quantified variation in floral design by scoring floral symmetry, corolla fusion, floral orientation and stamen number. We confirm the importance of four floral character states (bilateral symmetry, fused corollas, horizontal orientation and reduced stamen number) in promoting precise pollen placement on diverse pollinators. Our findings provide phylogenetically corrected, empirical support that the evolution of the four floral characters reflect selection for enhanced precision of pollen placed on pollinators.
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Affiliation(s)
- Alyssa B Stewart
- Department of Plant Science, Faculty of Science, Mahidol University, Bangkok, 10400, Thailand
| | - Carolina Diller
- Department of Plant Protection Biology, Swedish University of Agricultural Sciences, Alnarp, 234 56, Sweden
| | - Michele R Dudash
- Department of Natural Resource Management, South Dakota State University, Brookings, SD, 57007, USA
- Department of Biology, University of Maryland, College Park, MD, 20742, USA
| | - Charles B Fenster
- Oak Lake Field Station, South Dakota State University, Brookings, SD, 57007, USA
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Mochizuki J, Itagaki T, Aoyagi Blue Y, Ito M, Sakai S. Ovule and seed production patterns in relation to flower size variations in actinomorphic and zygomorphic flower species. AOB PLANTS 2019; 11:plz061. [PMID: 31656557 PMCID: PMC6804480 DOI: 10.1093/aobpla/plz061] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Accepted: 09/14/2019] [Indexed: 06/10/2023]
Abstract
Zygomorphic flower species tend to show lower flower size variation than actinomorphic flower species. Have these differences also brought an association in ovule and seed production that has arisen due to natural selection in these species? Flowers were collected from 29 actinomorphic and 20 zygomorphic flower species, and fruits were collected from 21 actinomorphic and 14 zygomorphic flower species in Miyagi and Aomori prefectures, in Japan. The coefficient of variations (CVs) of flower sizes, mean ovule sizes of flowers, ovule numbers of flowers and mean seed sizes of fruits were calculated. The CV of flower sizes was marginally different between the floral symmetry types; tending to be lower in the zygomorphic flower species than in the actinomorphic flower species. The CVs of mean ovule sizes and ovule numbers of flowers increased with increase in the CV of flower sizes in the actinomorphic flower species but not in the zygomorphic flower species. Mean ovule number of flowers tends to increase with increase in mean flower size in the actinomorphic flower species but not in the zygomorphic flower species. The degrees in variations in ovule size and number of flowers were influenced by the interaction of floral symmetry type and flower size variation, suggesting that floral symmetry also has brought an evolutionary association in ovule production by flowers.
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Affiliation(s)
- Jun Mochizuki
- Graduate School of Life Sciences, Tohoku University, Aoba, Sendai, Japan
| | - Tomoyuki Itagaki
- Graduate School of Life Sciences, Tohoku University, Aoba, Sendai, Japan
| | - Yuta Aoyagi Blue
- Graduate School of Life Sciences, Tohoku University, Aoba, Sendai, Japan
| | - Masaya Ito
- Graduate School of Life Sciences, Tohoku University, Aoba, Sendai, Japan
| | - Satoki Sakai
- Graduate School of Life Sciences, Tohoku University, Aoba, Sendai, Japan
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Barazani O, Erez T, Ogran A, Hanin N, Barzilai M, Dag A, Shafir S. Natural Variation in Flower Color and Scent in Populations of Eruca sativa (Brassicaceae) Affects Pollination Behavior of Honey Bees. JOURNAL OF INSECT SCIENCE (ONLINE) 2019; 19:5489313. [PMID: 31087084 PMCID: PMC6516435 DOI: 10.1093/jisesa/iez038] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/04/2018] [Indexed: 06/09/2023]
Abstract
Plants of Eruca sativa Mill. (Brassicaceae) from desert and Mediterranean populations in Israel differ in flower color and size. In the desert habitat, the population has higher abundance of flowers with cream color and longer petals, whereas in the Mediterranean habitat, the population has higher abundance of flowers with yellow and shorter petals. Choice experiments with honey bee foragers (Apis mellifera Linn., Apidae, Hymenoptera), the main pollinator in the natural habitat in Israel, confirmed that they are more attracted to the yellow flower morph than to the cream one. A proboscis extension response test indicated that honey bees are able to discriminate between flower scents of the desert and Mediterranean populations. Considering the advantage of plants of the yellow morph in attracting pollinators, we further tested in a common garden experiment whether these possess higher fitness than plants of the desert population. Indeed, a significant association was found between flower color and fruit set, and seed mass. In general, our results provide evidence for ecotypic differentiation between populations imposed by pollinators. The advantage of the yellow color morph in attracting pollinators may explain its dominance among plants of the Mediterranean population. We discuss why the cream color morph may be dominant in the desert habitat, considering the possibility of different pollinators, tradeoffs between traits, or pleiotropy.
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Affiliation(s)
- Oz Barazani
- Institute of Plant Sciences, Israel Plant Gene Bank, Agricultural Research Organization, Rishon LeZion, Israel
| | - Tal Erez
- Institute of Plant Sciences, Israel Plant Gene Bank, Agricultural Research Organization, Rishon LeZion, Israel
- B. Triwaks Bee Research Center, Department of Entomology, The Hebrew University of Jerusalem, Faculty of Agriculture, Food, and the Environment, Rehovot, Israel
| | - Ariel Ogran
- Institute of Plant Sciences, Israel Plant Gene Bank, Agricultural Research Organization, Rishon LeZion, Israel
| | - Nir Hanin
- Institute of Plant Sciences, Israel Plant Gene Bank, Agricultural Research Organization, Rishon LeZion, Israel
| | - Michal Barzilai
- Institute of Plant Sciences, Israel Plant Gene Bank, Agricultural Research Organization, Rishon LeZion, Israel
| | - Arnon Dag
- Institute of Plant Sciences, Agricultural Research Organization, Gilat Research Station, Israel
| | - Sharoni Shafir
- B. Triwaks Bee Research Center, Department of Entomology, The Hebrew University of Jerusalem, Faculty of Agriculture, Food, and the Environment, Rehovot, Israel
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Nikkeshi A, Kurimoto D, Ushimaru A. Low flower-size variation in bilaterally symmetrical flowers: Support for the pollination precision hypothesis. AMERICAN JOURNAL OF BOTANY 2015; 102:2032-40. [PMID: 26656130 DOI: 10.3732/ajb.1500371] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2015] [Accepted: 11/09/2015] [Indexed: 05/28/2023]
Abstract
PREMISE OF THE STUDY The evolutionary shift from radial to bilateral symmetry in flowers is generally associated with the evolution of low flower-size variation. This phenomenon supports the hypothesis that the lower size variation in bilateral flowers can be attributed to low pollinator diversity. In this study, we propose two other hypotheses to explain low flower-size variation in bilateral symmetrical flowers. To test the three hypotheses, we examined the relative importance of pollinator diversity, composition, and bilateral symmetry itself as selective forces on low flower-size variation. METHODS We examined pollinator diversity and composition and flower-size variation for 36 species in a seminatural ecosystem with high bee richness and frequent lepidopteran visitation. KEY RESULTS Bilateral flowers were more frequently visited than radial flowers by larger bees, but functional-group diversity of the pollinators did not differ between symmetry types. Although bilateral flowers had significantly lower flower-size variation than radial flowers, flower-size variation did not vary with pollinator diversity and composition but was instead related to bilateral symmetry. CONCLUSIONS Our results suggest that the lower size variation in bilateral flowers might have evolved under selection favoring the control of pollinator behavior on flowers to enhance the accurate placement of pollen on the body of the pollinator, independent of pollinator type. Because of the limited research on this issue, future work should be conducted in various types of plant-pollinator communities worldwide to further clarify the issue.
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Affiliation(s)
- Aoi Nikkeshi
- Graduate school of Human Development and Environment, Kobe University, 3-11 Tsurukabuto, Nada, Kobe 657-8501, Japan
| | - Daiki Kurimoto
- Faculty of Human Development, Kobe University, 3-11 Tsurukabuto, Nada, Kobe 657-8501, Japan
| | - Atushi Ushimaru
- Graduate school of Human Development and Environment, Kobe University, 3-11 Tsurukabuto, Nada, Kobe 657-8501, Japan Faculty of Human Development, Kobe University, 3-11 Tsurukabuto, Nada, Kobe 657-8501, Japan
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Lázaro A, Totland O. The influence of floral symmetry, dependence on pollinators and pollination generalization on flower size variation. ANNALS OF BOTANY 2014; 114:157-65. [PMID: 24838838 PMCID: PMC4071101 DOI: 10.1093/aob/mcu083] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2013] [Accepted: 04/02/2014] [Indexed: 05/25/2023]
Abstract
BACKGROUND AND AIMS The pollinator-mediated stabilizing selection hypothesis suggests that the specialized pollination system of zygomorphic flowers might cause stabilizing selection, reducing their flower size variation compared with actinomorphic flowers. However, the degree of ecological generalization and of dependence on pollinators varies greatly among species of both flower symmetry types and this may also affect flower size variation. METHODS Data on 43 species from two contrasting communities (one alpine and one lowland community) were used to test the relationships and interactions between flower size phenotypic variation, floral symmetry, ecological pollination generalization and species' dependence on pollinators. KEY RESULTS Contrary to what was expected, higher flower size variation was found in zygomorphic than in actinomorphic species in the lowland community, and no difference in flower size variation was found between symmetry types in the alpine community. The relationship between floral symmetry and flower size variation depended on ecological generalization and species' dependence on pollinators, although the influence of ecological generalization was only detected in the alpine community. Zygomorphic species that were highly dependent on pollinators and that were ecologically specialized were less variable in flower size than ecologically generalist and selfing zygomorphic species, supporting the pollinator-mediated stabilizing selection hypothesis. However, these relationships were not found in actinomorphic species, probably because they are not dependent on any particular pollinator for efficient pollination and therefore their flower size always shows moderate levels of variation. CONCLUSIONS The study suggests that the relationship between flower size variation and floral symmetry may be influenced by population-dependent factors, such as ecological generalization and species' dependence on pollinators.
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Affiliation(s)
- A Lázaro
- Mediterranean Institute for Advanced Studies, C/ Miquel Marqués 21, 07190, Esporles, Balearic Islands, Spain
| | - O Totland
- Norwegian University of Life Sciences, Department of Ecology and Natural Resource Management, PO Box 5003 Ås, Norway
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Ma Y, Xie W, Tian X, Sun W, Wu Z, Milne R. Unidirectional hybridization and reproductive barriers between two heterostylous primrose species in north-west Yunnan, China. ANNALS OF BOTANY 2014; 113:763-75. [PMID: 24492637 PMCID: PMC3962241 DOI: 10.1093/aob/mct312] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2013] [Accepted: 12/13/2013] [Indexed: 05/14/2023]
Abstract
BACKGROUND AND AIMS Heteromorphy in flowers has a profound effect on breeding patterns within a species, but little is known about how it affects reproductive barriers between species. The heterostylous genus Primula is very diverse in the Himalaya region, but hybrids there have been little researched. This study examines in detail a natural hybrid zone between P. beesiana and P. bulleyana. METHODS Chloroplast sequencing, AFLP (amplified fragment length polymorphism) markers and morphological comparisons were employed to characterize putative hybrids in the field, using synthetic F1s from hand pollination as controls. Pollinator visits to parent species and hybrids were observed in the field. Hand pollinations were conducted to compare pollen tube growth, seed production and seed viability for crosses involving different morphs, species and directions of crossing. KEY RESULTS Molecular data revealed all hybrid derivatives examined to be backcrosses of first or later generations towards P. bulleyana: all had the chloroplast DNA (cpDNA) of this species. Some individuals had morphological traits suggesting they were hybrids, but they were genetically similar to P. bulleyana; they might have been advanced generation backcrosses. Viable F1s could not be produced with P. bulleyana pollen on P. beesiana females, irrespective of the flower morphs used. Within-morph crosses for each species had very low (<10 %) seed viability, whereas crosses between pin P. bulleyana (female) and pin P. beesiana had a higher seed viability of 30 %. Thus genetic incompatibility mechanisms back up mechanical barriers to within-morph crosses in each species, but are not the same between the two species. The two species share their main pollinators, and pollinators were observed to fly between P. bulleyana and hybrids, suggesting that pollinator behaviour may not be an important isolating factor. CONCLUSIONS Hybridization is strongly asymmetric, with P. bulleyana the only possible mother and all detected hybrids being backcrosses in this direction. Partial ecological isolation and inhibition of heterospecific pollen, and possibly complete barriers to F1 formation on P. beesiana, may be enough to make F1 formation very rare in these species. Therefore, with no F1 detected, this hybrid zone may have a finite life span as successive generations become more similar to P. bulleyana.
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Affiliation(s)
- Yongpeng Ma
- Kunming Botanical Garden, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, PR China
| | - Weijia Xie
- Flower research institute, Yunnan Academy of Agriculture Sciences, Kunming 650201, PR China
| | - Xiaoling Tian
- Kunming Botanical Garden, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, PR China
| | - Weibang Sun
- Kunming Botanical Garden, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, PR China
| | - Zhikun Wu
- Kunming Botanical Garden, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, PR China
| | - Richard Milne
- Institute of Molecular Plant Sciences, University of Edinburgh, Edinburgh EH9 3JH, UK
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Pélabon C, Armbruster WS, Hansen TF. Experimental evidence for the Berg hypothesis: vegetative traits are more sensitive than pollination traits to environmental variation. Funct Ecol 2010. [DOI: 10.1111/j.1365-2435.2010.01770.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Christophe Pélabon
- Department of Biology, Centre for Conservation Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway
| | - W. Scott Armbruster
- Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway
- School of Biological Sciences, King Henry Building, University of Portsmouth, Portsmouth PO1 2DY, UK
- Institute of Arctic Biology, University of Alaska, Fairbanks, Alaska 99775, USA
| | - Thomas F. Hansen
- Department of Biology, Centre for Ecological and Evolutionary Synthesis, University of Oslo, 0316 Oslo, Norway
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Gong YB, Huang SQ. Floral symmetry: pollinator-mediated stabilizing selection on flower size in bilateral species. Proc Biol Sci 2009; 276:4013-20. [PMID: 19710062 PMCID: PMC2825790 DOI: 10.1098/rspb.2009.1254] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2009] [Accepted: 08/05/2009] [Indexed: 11/12/2022] Open
Abstract
Pollinator-mediated stabilizing selection (PMSS) has been proposed as the driver of the evolutionary shift from radial to bilateral symmetry of flowers. Studies have shown that variation in flower size is lower in bilateral than in radial species, but whether bilateral flowers experience more stabilizing selection pressures by employing fewer, more specialized pollinators than radial flowers remains unclear. To test the PMSS hypothesis, we investigate plant-pollinator interactions from a whole community in an alpine meadow in Hengduan Mountains, China, to examine: (i) variance in flower size and level of ecological generalization (pollinator diversity calculated using functional groups) in 14 bilateral and 13 radial species and (ii) the role pollinator diversity played in explaining the difference of variance in flower size between bilateral and radial species. Our data showed that bilateral species had less variance in flower size and were visited by fewer pollinator groups. Pollinator diversity accounted for up to 40 per cent of the difference in variance in flower size between bilateral and radial species. The mediator effect of pollinator diversity on the relationship between floral symmetry and variance in flower size in the community is consistent with the PMSS hypothesis.
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Affiliation(s)
| | - Shuang-Quan Huang
- College of Life Sciences, Wuhan University, Wuhan 430072, People's Republic of China
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Harder LD, Johnson SD. Darwin's beautiful contrivances: evolutionary and functional evidence for floral adaptation. THE NEW PHYTOLOGIST 2009; 183:530-545. [PMID: 19552694 DOI: 10.1111/j.1469-8137.2009.02914.x] [Citation(s) in RCA: 221] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Although not 'a professed botanist', Charles Darwin made seminal contributions to understanding of floral and inflorescence function while seeking evidence of adaptation by natural selection. This review considers the legacy of Darwin's ideas from three perspectives. First, we examine the process of floral and inflorescence adaptation by surveying studies of phenotypic selection, heritability and selection responses. Despite widespread phenotypic and genetic capacity for natural selection, only one-third of estimates indicate phenotypic selection. Second, we evaluate experimental studies of floral and inflorescence function and find that they usually demonstrate that reproductive traits represent adaptations. Finally, we consider the role of adaptation in floral diversification. Despite different diversification modes (coevolution, divergent use of the same pollen vector, pollinator shifts), evidence of pollination ecotypes and phylogenetic patterns suggests that adaptation commonly contributes to floral diversity. Thus, this review reveals a contrast between the inconsistent occurrence of phenotypic selection and convincing experimental and comparative evidence that floral traits are adaptations. Rather than rejecting Darwin's hypotheses about floral evolution, this contrast suggests that the tempo of creative selection varies, with strong, consistent selection during episodes of diversification, but relatively weak and inconsistent selection during longer, 'normal' periods of relative phenotypic stasis.
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Affiliation(s)
- Lawrence D Harder
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4
| | - Steven D Johnson
- School of Biological and Conservation Sciences, University of KwaZulu-Natal, Private Bag X01 Scottsville, Pietermaritzburg 3209, South Africa
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Herrera J. Visibility vs. biomass in flowers: exploring corolla allocation in Mediterranean entomophilous plants. ANNALS OF BOTANY 2009; 103:1119-27. [PMID: 19258340 PMCID: PMC2707908 DOI: 10.1093/aob/mcp046] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
BACKGROUND AND AIMS While pollinators may in general select for large, morphologically uniform floral phenotypes, drought stress has been proposed as a destabilizing force that may favour small flowers and/or promote floral variation within species. METHODS The general validity of this concept was checked by surveying a taxonomically diverse array of 38 insect-pollinated Mediterranean species. The interplay between fresh biomass investment, linear size and percentage corolla allocation was studied. Allometric relationships between traits were investigated by reduced major-axis regression, and qualitative correlates of floral variation explored using general linear-model MANOVA. KEY RESULTS Across species, flowers were perfectly isometrical with regard to corolla allocation (i.e. larger flowers were just scaled-up versions of smaller ones and vice versa). In contrast, linear size and biomass varied allometrically (i.e. there were shape variations, in addition to variations in size). Most floral variables correlated positively and significantly across species, except corolla allocation, which was largely determined by family membership and floral symmetry. On average, species with bilateral flowers allocated more to the corolla than those with radial flowers. Plant life-form was immaterial to all of the studied traits. Flower linear size variation was in general low among conspecifics (coefficients of variation around 10 %), whereas biomass was in general less uniform (e.g. 200-400 mg in Cistus salvifolius). Significant among-population differences were detected for all major quantitative floral traits. CONCLUSIONS Flower miniaturization can allow an improved use of reproductive resources under prevailingly stressful conditions. The hypothesis that flower size reflects a compromise between pollinator attraction, water requirements and allometric constraints among floral parts is discussed.
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