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Larue C, Petit RJ. Harmful self-pollination drives gynodioecy in European chestnut, a self-incompatible tree. AMERICAN JOURNAL OF BOTANY 2024; 111:e16329. [PMID: 38708705 DOI: 10.1002/ajb2.16329] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2023] [Revised: 02/27/2024] [Accepted: 03/04/2024] [Indexed: 05/07/2024]
Abstract
PREMISE Gynodioecy is a rare sexual system in which two genders (sensu Lloyd, 1980), cosexuals and females, coexist. To survive, female plants must compensate for their lack of siring capacity and male attractiveness. In European chestnut (Castanea sativa), an outcrossing tree, self-pollination reduces fruit set in cosexual individuals because of late-acting self-incompatibility and early inbreeding depression. Could this negative sexual interaction explain the presence of females in this species? METHODS We studied gender variation in wild populations of European chestnut. In addition, we compared fruit set (the proportion of flowers giving fruits) and other key female fitness components as well as reproductive allocation between genders. We then performed emasculation experiments in cosexual trees, by removing nectar-producing fertile male inflorescences. We also removed sterile but nectar-producing male inflorescences from female trees, as a control. RESULTS We found a highly variable proportion of male-sterile individuals in the wild in European chestnut. In the experimental plot, trees from each gender had similar size, flower density, and burr set, but different fruit set. Removing nectar-producing male inflorescences from branches or entire trees increased fruit set in cosexual but not in female trees. CONCLUSIONS These results show that self-pollination impairs fruit set in cosexual trees. Female trees avoid these problems as they do not produce pollen but continue to attract pollinators thanks to their rewarding male-sterile inflorescences, resulting in a much higher fruit set than in cosexuals. This demonstrates that even outcrossed plants can benefit from the cessation of self-pollination, to the point that unisexuality can evolve.
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Affiliation(s)
- Clément Larue
- Univ. Bordeaux, INRAE, Biogeco, Cestas, 33610, France
- INVENIO, Maison Jeannette, Douville, 24140, France
| | - Rémy J Petit
- Univ. Bordeaux, INRAE, Biogeco, Cestas, 33610, France
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2
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Is There More to Within-plant Variation in Seed Size than Developmental Noise? Evol Biol 2021. [DOI: 10.1007/s11692-021-09544-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
AbstractWithin-plant variation in seed size may merely reflect developmental instability, or it may be adaptive in facilitating diversifying bet-hedging, that is, production of phenotypically diverse offspring when future environments are unpredictable. To test the latter hypothesis, we analyzed patterns of variation in seed size in 11 populations of the perennial vine Dalechampia scandens grown in a common greenhouse environment. We tested whether population differences in the mean and variation of seed size covaried with environmental predictability at two different timescales. We also tested whether within-plant variation in seed size was correlated with independent measures of floral developmental instability and increased under stressful conditions. Populations differed genetically in the amount of seed-size variation occurring among plants, among infructescences within plants, and among seeds within infructescences. Within-individual variation was not detectably correlated with measures of developmental instability and did not increase under stress, but it increased weakly with short-term environmental unpredictability of precipitation at the source-population site. These results support the hypothesis that greater variation in seed size is adaptive when environmental predictability is low.
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Hildesheim LS, Opedal ØH, Armbruster WS, Pélabon C. Quantitative and qualitative consequences of reduced pollen loads in a mixed-mating plant. Ecol Evol 2019; 9:14253-14260. [PMID: 31938516 PMCID: PMC6953568 DOI: 10.1002/ece3.5858] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Revised: 10/16/2019] [Accepted: 10/23/2019] [Indexed: 12/25/2022] Open
Abstract
Greater pollination intensity can enhance maternal plant fitness by increasing seed set and seed quality as a result of more intense pollen competition or enhanced genetic sampling. We tested experimentally these effects by varying the pollen load from a single pollen donor on stigmas of female flowers of Dalechampia scandens (Euphorbiaceae) and measuring the effects on seed number and seed mass. Seed set increased rapidly with pollen number at low to moderate pollen loads, and a maximum set of three seeds occurred with a mean pollen load of 19 pollen grains. We did not detect a trade-off between the number of seeds and seed mass within a fruit. Seed mass increased with increasing pollen load, supporting the hypothesis of enhanced seed quality via increased pollen-competition intensity or genetic sampling. These results suggest that maternal fitness increases with larger pollen loads, even when the fertilization success is already high. Our results further highlight the importance of high rates of pollen arrival onto stigmas, as mediated by reliable pollinators. Comparing the pollen-to-seed response curve obtained in this experiment with those observed in natural populations suggests that pollen limitation may be more severe in natural populations than predicted from greenhouse studies. These results also indicate that declines in pollinator abundance may decrease plant fitness through lowered seed quality before an effect on seed set is detected.
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Affiliation(s)
- Laura S. Hildesheim
- Department of BiologyCentre for Biodiversity DynamicsNorwegian University of Science and TechnologyNTNUTrondheimNorway
- Department of Biological SciencesUniversity of BergenBergenNorway
| | - Øystein H. Opedal
- Department of BiologyCentre for Biodiversity DynamicsNorwegian University of Science and TechnologyNTNUTrondheimNorway
| | - W. Scott Armbruster
- School of Biological SciencesUniversity of PortsmouthPortsmouthUK
- Institute of Arctic BiologyUniversity of AlaskaFairbanksAKUSA
| | - Christophe Pélabon
- Department of BiologyCentre for Biodiversity DynamicsNorwegian University of Science and TechnologyNTNUTrondheimNorway
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Hildesheim LS, Opedal ØH, Armbruster WS, Pélabon C. Fitness costs of delayed pollination in a mixed-mating plant. ANNALS OF BOTANY 2019; 124:869-881. [PMID: 31504153 PMCID: PMC6868360 DOI: 10.1093/aob/mcz141] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Accepted: 08/14/2019] [Indexed: 06/01/2023]
Abstract
BACKGROUND AND AIMS To predict the evolutionary consequences of pollinator declines, we need to understand the evolution of delayed autonomous self-pollination, which is expected to evolve as a mechanism of reproductive assurance when cross-pollination becomes unreliable. This involves estimating the costs of increased levels of selfing as well as those associated with floral senescence. METHODS We studied the mechanisms and costs of delayed self-pollination in the mixed-mating vine Dalechampia scandens (Euphorbiaceae) by first assessing among-population variation in herkogamy and dichogamy, which together determine the rate and timing of autonomous self-pollination. We then tested whether floral longevity responds plastically to delayed pollination. Finally, we assessed the costs of delayed self-pollination in terms of seed number and size, explicitly separating inbreeding depression from effects of floral senescence. KEY RESULTS Herkogamy varied extensively, while variation in dichogamy was more limited. Unpollinated blossoms increased their longevity, but seed quantity and quality decreased with increasing delays in pollination, independently of inbreeding depression. CONCLUSIONS In D. scandens, earlier autonomous selfing is facilitated by reduced herkogamy rather than reduced protogyny, providing reproductive assurance while maintaining the possibility for outcrossing events. Effective early autonomous self-pollination may evolve under reduced cross-pollination reliability in response to costs associated with floral senescence.
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Affiliation(s)
- Laura S Hildesheim
- Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, NTNU, Trondheim, Norway
| | - Øystein H Opedal
- Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, NTNU, Trondheim, Norway
- Research Centre for Ecological Change, Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland
| | - W Scott Armbruster
- School of Biological Sciences, King Henry Building, King Henry I Street, University of Portsmouth, Portsmouth, UK
- Institute of Arctic Biology, University of Alaska, Fairbanks, AK, USA
| | - Christophe Pélabon
- Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, NTNU, Trondheim, Norway
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Martins AA, Opedal ØH, Armbruster WS, Pélabon C. Rainfall seasonality predicts the germination behavior of a tropical dry-forest vine. Ecol Evol 2019; 9:5196-5205. [PMID: 31110672 PMCID: PMC6509399 DOI: 10.1002/ece3.5108] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2019] [Revised: 03/04/2019] [Accepted: 03/07/2019] [Indexed: 11/08/2022] Open
Abstract
Seed dormancy is considered to be an adaptive strategy in seasonal and/or unpredictable environments because it prevents germination during climatically favorable periods that are too short for seedling establishment. Tropical dry forests are seasonal environments where seed dormancy may play an important role in plant resilience and resistance to changing precipitation patterns. We studied the germination behavior of seeds from six populations of the Neotropical vine Dalechampia scandens (Euphorbiaceae) originating from environments of contrasting rainfall seasonality. Seeds produced by second greenhouse-generation plants were measured and exposed to a favorable wet environment at different time intervals after capsule dehiscence and seed dispersal. We recorded the success and the timing of germination. All populations produced at least some dormant seeds, but seeds of populations originating from more seasonal environments required longer periods of after-ripening before germinating. Within populations, larger seeds tended to require longer after-ripening periods than did smaller seeds. These results indicate among-population genetic differences in germination behavior and suggest that these populations are adapted to local environmental conditions. They also suggest that seed size may influence germination timing within populations. Ongoing changes in seasonality patterns in tropical dry forests may impose strong selection on these traits.
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Affiliation(s)
- Adriana A. Martins
- Department of Biology, Centre for Biodiversity DynamicsNorwegian University of Science and Technology, NTNUTrondheimNorway
| | - Øystein H. Opedal
- Department of Biology, Centre for Biodiversity DynamicsNorwegian University of Science and Technology, NTNUTrondheimNorway
- Faculty of Biological and Environmental Sciences, Research Centre for Ecological ChangeUniversity of HelsinkiHelsinkiFinland
| | - William Scott Armbruster
- School of Biological SciencesUniversity of PortsmouthPortsmouthUK
- Institute of Arctic BiologyUniversity of AlaskaFairbanksAlaska
| | - Christophe Pélabon
- Department of Biology, Centre for Biodiversity DynamicsNorwegian University of Science and Technology, NTNUTrondheimNorway
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Intersexual conflict over seed size is stronger in more outcrossed populations of a mixed-mating plant. Proc Natl Acad Sci U S A 2018; 115:11561-11566. [PMID: 30282740 DOI: 10.1073/pnas.1810979115] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
In polyandrous species, fathers benefit from attracting greater maternal investment toward their offspring at the expense of the offspring of other males, while mothers should usually allocate resources equally among offspring. This conflict can lead to an evolutionary arms race between the sexes, manifested through antagonistic genes whose expression in offspring depends upon the parent of origin. The arms race may involve an increase in the strength of maternally versus paternally derived alleles engaged in a "tug of war" over maternal provisioning or repeated "recognition-avoidance" coevolution where growth-enhancing paternally derived alleles evolve to escape recognition by maternal genes targeted to suppress their effect. Here, we develop predictions to distinguish between these two mechanisms when considering crosses among populations that have reached different equilibria in this intersexual arms race. We test these predictions using crosses within and among populations of Dalechampia scandens (Euphorbiaceae) that presumably have experienced different intensities of intersexual conflict, as inferred from their historical differences in mating system. In crosses where the paternal population was more outcrossed than the maternal population, hybrid seeds were larger than those normally produced in the maternal population, whereas when the maternal population was more outcrossed, hybrid seeds were smaller than normal. These results confirm the importance of mating systems in determining the intensity of intersexual conflict over maternal investment and provide strong support for a tug-of-war mechanism operating in this conflict. They also yield clear predictions for the fitness consequences of gene flow among populations with different mating histories.
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Peters MAE, Weis AE. Selection for pollen competitive ability in mixed-mating systems. Evolution 2018; 72:2513-2536. [DOI: 10.1111/evo.13597] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2017] [Accepted: 08/10/2018] [Indexed: 12/26/2022]
Affiliation(s)
- Madeline A. E. Peters
- Department of Ecology and Evolutionary Biology; University of Toronto; 25 Willcocks Street Toronto ON M5S 3B2 Canada
| | - Arthur E. Weis
- Department of Ecology and Evolutionary Biology; University of Toronto; 25 Willcocks Street Toronto ON M5S 3B2 Canada
- Koffler Scientific Reserve at Jokers Hill; University of Toronto; 17000 Dufferin Street King City ON L7B 1K5 Canada
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Williams JH, Mazer SJ. Pollen--tiny and ephemeral but not forgotten: New ideas on their ecology and evolution. AMERICAN JOURNAL OF BOTANY 2016; 103:365-74. [PMID: 26980838 DOI: 10.3732/ajb.1600074] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Accepted: 02/29/2016] [Indexed: 05/08/2023]
Abstract
Ecologists and evolutionary biologists have been interested in the functional biology of pollen since the discovery in the 1800s that pollen grains encompass tiny plants (male gametophytes) that develop and produce sperm cells. After the discovery of double fertilization in flowering plants, botanists in the early 1900s were quick to explore the effects of temperature and maternal nutrients on pollen performance, while evolutionary biologists began studying the nature of haploid selection and pollen competition. A series of technical and theoretic developments have subsequently, but usually separately, expanded our knowledge of the nature of pollen performance and how it evolves. Today, there is a tremendous diversity of interests that touch on pollen performance, ranging from the ecological setting on the stigma, structural and physiological aspects of pollen germination and tube growth, the form of pollen competition and its role in sexual selection in plants, virus transmission, mating system evolution, and inbreeding depression. Given the explosion of technical knowledge of pollen cell biology, computer modeling, and new methods to deal with diversity in a phylogenetic context, we are now more than ever poised for a new era of research that includes complex functional traits that limit or enhance the evolution of these deceptively simple organisms.
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Affiliation(s)
- Joseph H Williams
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996 USA
| | - Susan J Mazer
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, California 93105 USA
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Husband BC. Effect of inbreeding on pollen tube growth in diploid and tetraploid Chamerion angustifolium: Do polyploids mask mutational load in pollen? AMERICAN JOURNAL OF BOTANY 2016; 103:532-40. [PMID: 26944354 DOI: 10.3732/ajb.1500243] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2015] [Accepted: 10/21/2015] [Indexed: 05/16/2023]
Abstract
PREMISE OF THE STUDY Deleterious recessive mutations are an important determinant of fitness (mutational load) in the sporophytic phase of plants and a major cause of inbreeding depression; however, their role in gametophyte function is less well documented but may account for variation in pollen tube growth and siring ability, especially between diploid and polyploid plants, which can mask the load. METHODS We investigated the role of mutational load in pollen performance using the perennial polyploid Chamerion angustifolium by comparing tube growth of pollen, in styles and in growth medium, from inbred (selfed) and outbred diploids to that of inbred and outbred tetraploids. Pollen from tetraploids is expected to mask deleterious mutations more effectively in the outbred condition but reveal them after inbreeding. In contrast, gametophytes from diploids should express the same genetic load in inbred or outbred plants. KEY RESULTS Pollen tube growth measured in growth medium was highest in outbred tetraploids and generally lower in inbred than outbred plants. The effect of selfing was significant in pollen from tetraploids but not diploids. The differential effect of selfing was also evident in the proportion of pollen reaching the base of styles, but the ploidy × pollination interaction was not significant. Selfing also had a negative effect on sporophyte fitness but was greater in diploids than tetraploids. CONCLUSIONS Pollen performance is influenced by the expression of mutational load, which is masked in polyploids. This effect may partly explain strong siring success of tetraploids in this species.
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Affiliation(s)
- Brian C Husband
- Department of Integrative Biology, University of Guelph, 50 Stone Road E., Guelph, Ontario, N1G 2W1 Canada
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10
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Opedal ØH, Armbruster WS, Pélabon C. Inbreeding effects in a mixed-mating vine: effects of mating history, pollen competition and stress on the cost of inbreeding. AOB PLANTS 2015; 7:plv133. [PMID: 26578744 PMCID: PMC4683981 DOI: 10.1093/aobpla/plv133] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Accepted: 11/07/2015] [Indexed: 06/01/2023]
Abstract
Inbreeding depression is assumed to be a central factor contributing to the stability of plant mating systems. Predicting the fitness consequence of inbreeding in natural populations is complicated, however, because it may be affected by the mating histories of populations generating variation in the amount of purging of deleterious alleles. Furthermore, the level of inbreeding depression may depend on environmental conditions and the intensity of pollen competition. In a greenhouse experiment comparing four populations of the neotropical vine Dalechampia scandens (Euphorbiaceae), we tested whether inbreeding depression for early-life fitness depended on the inferred mating history of each population, as indicated by genetically determined differences in herkogamy and autofertility rates. We also tested whether the intensity of pollen competition and the level of stress encountered by the seeds and seedlings affected the amount of inbreeding depression observed. Herkogamy was a good predictor of autofertility in each population. However, we found only limited evidence for inbreeding depression in any population, and inbreeding depression varied independently of the intensity of pollen competition and amount of stress encountered by the seeds and seedlings. Thus, the population's rate of autofertility did not predict the amount of inbreeding depression. Overall, we found no evidence supporting the expectations that more inbred populations experience less inbreeding depression, and that pollen competition reduces the cost of inbreeding. These results suggest that additional factors may be responsible for the maintenance of the mixed mating systems of D. scandens populations.
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Affiliation(s)
- Øystein H Opedal
- Centre for Biodiversity Dynamics, Department of 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, University of Portsmouth, King Henry Building, King Henry I Street, Portsmouth PO1 2DY, UK Institute of Arctic Biology, University of Alaska, Fairbanks, AK 99775, USA
| | - Christophe Pélabon
- Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway
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Pélabon C, Albertsen E, Falahati-Anbaran M, Wright J, Armbruster W. Does multiple paternity affect seed mass in angiosperms? An experimental test in Dalechampia scandens. J Evol Biol 2015; 28:1719-33. [DOI: 10.1111/jeb.12692] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2015] [Revised: 06/17/2015] [Accepted: 07/07/2015] [Indexed: 11/29/2022]
Affiliation(s)
- C. Pélabon
- Department of Biology; Centre for Biodiversity Dynamics; Norwegian University of Science and Technology; Trondheim Norway
| | - E. Albertsen
- Department of Biology; Centre for Biodiversity Dynamics; Norwegian University of Science and Technology; Trondheim Norway
| | - M. Falahati-Anbaran
- School of Biology and Center of Excellence in Phylogeny of Living Organisms; University of Tehran; Tehran Iran
- Department of Biology; Norwegian University of Science and Technology; Trondheim Norway
| | - J. Wright
- Department of Biology; Centre for Biodiversity Dynamics; Norwegian University of Science and Technology; Trondheim Norway
| | - W.S. Armbruster
- Department of Biology; Norwegian University of Science and Technology; Trondheim Norway
- School of Biological Sciences; King Henry Building; University of Portsmouth; Portsmouth UK
- Institute of Arctic Biology; University of Alaska; Fairbanks AK USA
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