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Brown KS, Caruso CM. The effect of experimental pollinator decline on pollinator-mediated selection on floral traits. Ecol Evol 2023; 13:e10706. [PMID: 37953983 PMCID: PMC10636310 DOI: 10.1002/ece3.10706] [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: 09/13/2023] [Accepted: 10/22/2023] [Indexed: 11/14/2023] Open
Abstract
Human-mediated environmental change, by reducing mean fitness, is hypothesized to strengthen selection on traits that mediate interactions among species. For example, human-mediated declines in pollinator populations are hypothesized to reduce mean seed production by increasing the magnitude of pollen limitation and thus strengthen pollinator-mediated selection on floral traits that increase pollinator attraction or pollen transfer efficiency. To test this hypothesis, we measured two female fitness components and six floral traits of Lobelia siphilitica plants exposed to supplemental hand-pollination, ambient open-pollination, or reduced open-pollination treatments. The reduced treatment simulated pollinator decline, while the supplemental treatment was used to estimate pollen limitation and pollinator-mediated selection. We found that plants in the reduced pollination treatment were significantly pollen limited, resulting in pollinator-mediated selection for taller inflorescences and more vibrant petals, both traits that could increase pollinator attraction. This contrasts with plants in the ambient pollination treatment, where reproduction was not pollen limited and there was not significant pollinator-mediated selection on any floral trait. Our results support the hypothesis that human-mediated environmental change can strengthen selection on traits of interacting species and suggest that these traits have the potential to evolve in response to changing environments.
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Affiliation(s)
- Kaitlyn S. Brown
- Department of Integrative BiologyUniversity of GuelphGuelphOntarioCanada
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García Y, Dow BS, Parachnowitsch AL. Water deficit changes patterns of selection on floral signals and nectar rewards in the common morning glory. AOB PLANTS 2023; 15:plad061. [PMID: 37899982 PMCID: PMC10601024 DOI: 10.1093/aobpla/plad061] [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: 03/20/2023] [Accepted: 08/24/2023] [Indexed: 10/31/2023]
Abstract
Understanding whether and how resource limitation alters phenotypic selection on floral traits is key to predict the evolution of plant-pollinator interactions under climate change. Two important resources predicted to decline with our changing climate are pollinators and water in the form of increased droughts. Most work, however, has studied these selective agents separately and in the case of water deficit, studies are rare. Here, we use the common morning glory (Ipomoea purpurea) to investigate the effects of experimental reduction in pollinator access and water availability on floral signals and nectar rewards and their effects on phenotypic selection on these traits. We conducted a manipulative experiment in a common garden, where we grew plants in three treatments: (1) pollinator restriction, (2) water reduction and (3) unmanipulated control. Plants in pollinator restriction and control treatments were well-watered compared to water deficit. We found that in contrast to pollinator restriction, water deficit had strong effects altering floral signals and nectar rewards but also differed in the direction and strength of selection on these traits compared to control plants. Water deficit increased the opportunity for selection, and selection in this treatment favoured lower nectar volumes and larger floral sizes, which might further alter pollinator visitation. In addition, well-watered plants, both in control and pollinator deficit, showed similar patterns of selection to increase nectar volume suggesting non-pollinator-mediated selection on nectar. Our study shows that floral traits may evolve in response to reduction in water access faster than to declines in pollinators and reinforces that abiotic factors can be important agents of selection for floral traits. Although only few experimental selection studies have manipulated access to biotic and abiotic resources, our results suggest that this approach is key for understanding how pollination systems may evolve under climate change.
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Affiliation(s)
- Yedra García
- Department of Biology, University of New Brunswick, 10 Bailey Dr, Fredericton, NB E3B 5A3, Canada
| | - Benjamin S Dow
- Department of Biology, University of New Brunswick, 10 Bailey Dr, Fredericton, NB E3B 5A3, Canada
| | - Amy L Parachnowitsch
- Department of Biology, University of New Brunswick, 10 Bailey Dr, Fredericton, NB E3B 5A3, Canada
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Kwok A, Dorken ME. Sexual selection on male but not female function in monoecious and dioecious populations of broadleaf arrowhead ( Sagittaria latifolia). Proc Biol Sci 2022; 289:20220919. [PMID: 36350202 PMCID: PMC9653219 DOI: 10.1098/rspb.2022.0919] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2022] [Accepted: 10/12/2022] [Indexed: 09/30/2023] Open
Abstract
Direct measures of sexual selection in plants are rare and complicated by immobility and modular growth. For plants, instantaneous measures of fitness typically scale with size, but covariances between size and mating success could obscure the detection of sexual selection. We measured the magnitude of sexual selection in a monoecious and a dioecious population of the clonal plant Sagittaria latifolia using Bateman gradients (ßss). These gradients were calculated using parentage analysis and residual regression to account for the effects of shoot and clone size on mating and reproductive success. In both populations, (i) there was greater promiscuity via male function than via female function and (ii) ßss were positive, with significant associations between mating and reproductive success for male but not female function. Moreover, estimated βss were similar for the monoecious and dioecious populations, possibly because non-overlapping female and male sex phases in hermaphroditic S. latifolia reduced the scope for interference between sex functions during mating. This study builds on previous studies of selection on plant mating traits, and of sexual selection under experimental conditions, by showing that sexual selection can operate in natural populations of plants, including populations of hermaphrodites.
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Affiliation(s)
- Allison Kwok
- Environmental and Life Sciences Graduate Program, Trent University, Peterborough, ON, Canada K9J 0G2
| | - Marcel E. Dorken
- Department of Biology, Trent University, Peterborough, ON, Canada K9J 0G2
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Panique H, Caruso CM. Simulated pollinator declines intensify selection on floral traits that facilitate selfing and outcrossing in Impatiens capensis. AMERICAN JOURNAL OF BOTANY 2020; 107:148-154. [PMID: 31828763 DOI: 10.1002/ajb2.1403] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2019] [Accepted: 11/07/2019] [Indexed: 06/10/2023]
Abstract
PREMISE Anthropogenic environmental change is causing pollinator populations to decline. These declines should intensify selection for floral traits that facilitate outcrossing by making plants more attractive to pollinators and/or for floral traits that facilitate selfing in the absence of pollinators. However, the effect of pollinator declines on selection on floral traits could be modified by other environmental factors such as herbivores. METHODS We studied the effect of simulated pollinator declines on selection on floral traits of Impatiens capensis, a mixed-mating species that produces both obligately selfing cleistogamous flowers and primarily outcrossing chasmogamous flowers. We measured directional selection differentials via seeds per plant on two traits that facilitate outcrossing (chasmogamous flower size and number) and one trait that facilitates selfing (cleistogamous flower number) in ambient, reduced pollinator access, and reduced pollinator access combined with increased foliar herbivory treatments. RESULTS Reduced pollinator access intensified selection for larger chasmogamous flowers and more cleistogamous flowers. In contrast, increased herbivory did not affect selection on any floral trait. CONCLUSIONS Reduced pollinator access intensified selection for a trait that facilitates outcrossing, suggesting that even species such as I. capensis that can autonomously self-pollinate have the potential to respond to pollinator declines by evolving floral traits that reinforce interactions between plants and pollinators. However, reduced pollinator access also intensified selection for a trait that facilitates selfing, suggesting that I. capensis could adapt to pollinator declines by evolving floral traits that maintain the production of both selfed and outcrossed seeds.
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Affiliation(s)
- Hazel Panique
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada
| | - Christina M Caruso
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada
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Henshaw JM, Jennions MD, Kruuk LEB. How to quantify (the response to) sexual selection on traits. Evolution 2018; 72:1904-1917. [PMID: 30004126 DOI: 10.1111/evo.13554] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2018] [Revised: 06/16/2018] [Accepted: 07/07/2018] [Indexed: 01/01/2023]
Abstract
Natural selection operates via fitness components like mating success, fecundity, and longevity, which can be understood as intermediaries in the causal process linking traits to fitness. In particular, sexual selection occurs when traits influence mating or fertilization success, which, in turn, influences fitness. We show how to quantify both these steps in a single path analysis, leading to better estimates of the strength of sexual selection. Our model controls for confounding variables, such as body size or condition, when estimating the relationship between mating and reproductive success. Correspondingly, we define the Bateman gradient and the Jones index using partial rather than simple regressions, which better captures how they are commonly interpreted. The model can be applied both to purely phenotypic data and to quantitative genetic parameters estimated using information on relatedness. The phenotypic approach breaks down selection differentials into a sexually selected and a "remainder" component. The quantitative genetic approach decomposes the estimated evolutionary response to selection analogously. We apply our method to analyze sexual selection in male dusky pipefish, Syngnathus floridae, and in two simulated datasets. We highlight conceptual and statistical limitations of previous path-based approaches, which can lead to substantial misestimation of sexual selection.
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Affiliation(s)
- Jonathan M Henshaw
- Division of Ecology and Evolution, Research School of Biology, The Australian National University, Acton, ACT 2601, Canberra, Australia.,Institute of Zoology, University of Graz, Universitätsplatz 2, Graz, 8010, Austria
| | - Michael D Jennions
- Division of Ecology and Evolution, Research School of Biology, The Australian National University, Acton, ACT 2601, Canberra, Australia
| | - Loeske E B Kruuk
- Division of Ecology and Evolution, Research School of Biology, The Australian National University, Acton, ACT 2601, Canberra, Australia
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Dai C, Luo WJ, Gong YB, Liu F, Wang ZX. Resource reallocation patterns within Sagittaria trifolia inflorescences following differential pollination. AMERICAN JOURNAL OF BOTANY 2018; 105:803-811. [PMID: 29710426 DOI: 10.1002/ajb2.1053] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Accepted: 01/29/2018] [Indexed: 06/08/2023]
Abstract
PREMISE OF THE STUDY Understanding resource allocation to reproduction, a key factor in life history tradeoffs, has long intrigued plant ecologists. Despite the recognized importance of understanding the movement of resources among flowers following variable pollination, the patterns of resource reallocation to plant reproductive organs have not been thoroughly addressed. In this study, we aimed to empirically explore how resources redistribute within inflorescences in response to differential pollination intensities. METHODS Using a common herb, Sagittaria trifolia, we conducted supplemental and controlled pollination for single, some, or all flowers in simple and complex inflorescences, and compared their resulting fruiting probabilities, seed production, and average seed masses. KEY RESULTS Pollen supplementation of a single flower significantly increased its fruiting probability; however, the same manipulation of an inflorescence did not increase its overall reproduction. Single pollen-supplemented flowers had a higher percentage fruit set than inflorescences receiving supplemental pollination. In complex inflorescences, supplemental pollination had no effect on the reproductive success of flowers on the lateral or main branches. CONCLUSIONS We provided evidence of resource reallocation from controlled to pollen-supplemented flowers in simple inflorescences; however, resources were unlikely to be reallocated between the main and lateral branches in the complex inflorescences, suggesting that flowering branches represent integrated physiological units in S. trifolia. The results also demonstrated that single-flower supplemental pollination would exaggerate pollen limitation and lead to a biased understanding of a plant's reproductive status.
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Affiliation(s)
- Can Dai
- School of Resources and Environmental Science, Hubei University, Wuhan, 430062, China
- Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Wuhan, 430062, China
- Hubei Key Laboratory of Regional Development and Environmental Response (Hubei University), Wuhan, 430062, China
| | - Wen-Jie Luo
- School of Resources and Environmental Science, Hubei University, Wuhan, 430062, China
| | - Yan-Bing Gong
- State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, 430072, China
| | - Fan Liu
- Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, 430074, China
| | - Zheng-Xiang Wang
- School of Resources and Environmental Science, Hubei University, Wuhan, 430062, China
- Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Wuhan, 430062, China
- Hubei Key Laboratory of Regional Development and Environmental Response (Hubei University), Wuhan, 430062, China
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Dorken ME, Perry LE. Correlated paternity measures mate monopolization and scales with the magnitude of sexual selection. J Evol Biol 2016; 30:377-387. [DOI: 10.1111/jeb.13013] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Revised: 11/03/2016] [Accepted: 11/09/2016] [Indexed: 01/03/2023]
Affiliation(s)
- M. E. Dorken
- Department of Biology; Trent University; Peterborough ON Canada
| | - L. E. Perry
- Department of Biology; Trent University; Peterborough ON Canada
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Dai C, Liang X, Ren J, Liao M, Li J, Galloway LF. The mean and variability of a floral trait have opposing effects on fitness traits. ANNALS OF BOTANY 2016; 117:421-9. [PMID: 26749589 PMCID: PMC4765544 DOI: 10.1093/aob/mcv189] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Accepted: 11/05/2015] [Indexed: 05/03/2023]
Abstract
BACKGROUND AND AIMS Floral traits are essential for ensuring successful pollination and reproduction in flowering plants. In particular, style and anther positions are key for pollination accuracy and efficiency. Variation in these traits among individuals has been well studied, but less is known about variation within flowers and plants and its effect on pollination and reproductive success. METHODS Style deflexion is responsible for herkogamy and important for pollen deposition in Passiflora incarnata. The degree of deflexion may vary among stigmas within flowers as well as among flowers. We measured the variability of style deflexion at both the flower and the plant level. The fitness consequences of the mean and variation of style deflexion were then evaluated under natural pollination by determining their relationship to pollen deposition, seed production and average seed weight using structural equation modelling. In addition, the relationship between style deflexion and self-pollen deposition was estimated in a greenhouse experiment. KEY RESULTS We found greater variation in style deflexion within flowers and plants than among plants. Variation of style deflexion at the flower and plant level was positively correlated, suggesting that variability in style deflexion may be a distinct trait in P. incarnata. Lower deflexion and reduced variation in that deflexion increased pollen deposition, which in turn increased seed number. However, lower styles also increased self-pollen deposition. In contrast, higher deflexion and greater variability of that deflexion increased variation in pollen deposition, which resulted in heavier seeds. CONCLUSIONS Variability of style deflexion and therefore stigma placement, independent from the mean, appears to be a property of individual P. incarnata plants. The mean and variability of style deflexion in P. incarnata affected seed number and seed weight in contrasting ways, through the quantity and potentially quality of pollen deposition. This antagonistic selection via different fitness components may maintain diverse style phenotypes.
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Affiliation(s)
- Can Dai
- School of Resources and Environmental Science, Hubei University, Wuhan 430062, China, Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Wuhan 430062, China, Hubei Provincial Key Laboratory of Regional Development and Environmental Response, Wuhan 430062, China and
| | - Xijian Liang
- School of Resources and Environmental Science, Hubei University, Wuhan 430062, China
| | - Jie Ren
- Department of Biology, University of Virginia, Charlottesville, VA 22903, USA
| | - Minglin Liao
- School of Resources and Environmental Science, Hubei University, Wuhan 430062, China
| | - Jiyang Li
- School of Resources and Environmental Science, Hubei University, Wuhan 430062, China
| | - Laura F Galloway
- Department of Biology, University of Virginia, Charlottesville, VA 22903, USA
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Marshall DL, Evans AS. Can selection on a male mating character result in evolutionary change? A selection experiment on California wild radish, Raphanus sativus. AMERICAN JOURNAL OF BOTANY 2016; 103:553-567. [PMID: 26872491 DOI: 10.3732/ajb.1500171] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Accepted: 09/25/2015] [Indexed: 06/05/2023]
Abstract
PREMISE OF THE STUDY Whenever more pollen grains arrive on stigmas than necessary to fertilize ovules, sexual selection is possible. However, the role of sexual selection remains controversial, in part because of lack of evidence on genetic bases of traits and the response of relevant characters to selection. METHODS In an experiment with Raphanus sativus, we selected on tendency to sire seeds in the stylar or basal regions of fruits. This character is likely related to pollen tube growth rate, and seed position affects rates of abortion and seed predation. We measured differences among families in seed siring and related characters and evaluated responses to selection. KEY RESULTS All replicates showed strong effects of pollen donor family on proportion of seeds sired per fruit in mixed pollinations. Most also showed effects of pollen donor family on number of pollen grains per flower and pollen diameter. Two of four replicates showed a response to selection on position of seeds sired. In responding replicates, we found trade-offs in pollen grain size and number; plants with larger pollen grains sired more seeds in the basal region. CONCLUSIONS Our data suggest a genetic basis for pollen donor ability to sire seeds in competition. The significant response to selection in two replicates shows that position of seeds sired can respond to selection. Thus, all components for sexual selection to occur and affect traits are present. Variation in results among replicates might be due to changes in greenhouse conditions. Environmental effects may contribute to the maintenance of variation in these fitness-related characters.
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Affiliation(s)
- Diane L Marshall
- Department of Biology, MSC03-2020, 1 University of New Mexico, Albuquerque, New Mexico 87131 USA
| | - Ann S Evans
- Department of Biology, 99 Thomas Nelson Drive, Thomas Nelson Community College, Hampton, Virginia 23666 USA
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