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Gutiérrez-Valencia J, Fracassetti M, Horvath R, Laenen B, Désamore A, Drouzas AD, Friberg M, Kolář F, Slotte T. Genomic Signatures of Sexual Selection on Pollen-Expressed Genes in Arabis alpina. Mol Biol Evol 2021; 39:6456311. [PMID: 34878144 PMCID: PMC8788238 DOI: 10.1093/molbev/msab349] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Fertilization in angiosperms involves the germination of pollen on the stigma, followed by the extrusion of a pollen tube that elongates through the style and delivers two sperm cells to the embryo sac. Sexual selection could occur throughout this process when male gametophytes compete for fertilization. The strength of sexual selection during pollen competition should be affected by the number of genotypes deposited on the stigma. As increased self-fertilization reduces the number of mating partners, and the genetic diversity and heterozygosity of populations, it should thereby reduce the intensity of sexual selection during pollen competition. Despite the prevalence of mating system shifts, few studies have directly compared the molecular signatures of sexual selection during pollen competition in populations with different mating systems. Here we analyzed whole-genome sequences from natural populations of Arabis alpina, a species showing mating system variation across its distribution, to test whether shifts from cross- to self-fertilization result in molecular signatures consistent with sexual selection on genes involved in pollen competition. We found evidence for efficient purifying selection on genes expressed in vegetative pollen, and overall weaker selection on sperm-expressed genes. This pattern was robust when controlling for gene expression level and specificity. In agreement with the expectation that sexual selection intensifies under cross-fertilization, we found that the efficacy of purifying selection on male gametophyte-expressed genes was significantly stronger in genetically more diverse and outbred populations. Our results show that intra-sexual competition shapes the evolution of pollen-expressed genes, and that its strength fades with increasing self-fertilization rates.
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Affiliation(s)
- Juanita Gutiérrez-Valencia
- Department of Ecology, Environment, and Plant Sciences, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
| | - Marco Fracassetti
- Department of Ecology, Environment, and Plant Sciences, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
| | - Robert Horvath
- Department of Ecology, Environment, and Plant Sciences, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
| | - Benjamin Laenen
- Department of Ecology, Environment, and Plant Sciences, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
| | - Aurélie Désamore
- Department of Ecology, Environment, and Plant Sciences, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
| | - Andreas D Drouzas
- Laboratory of Systematic Botany and Phytogeography, School of Biology, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - Magne Friberg
- Department of Biology, Lund University, Lund, Sweden
| | - Filip Kolář
- Department of Botany, Faculty of Science, Charles University, Prague, Czech Republic
| | - Tanja Slotte
- Department of Ecology, Environment, and Plant Sciences, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
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Peach K, Liu JW, Mazer SJ. Climate Predicts UV Floral Pattern Size, Anthocyanin Concentration, and Pollen Performance in Clarkia unguiculata. FRONTIERS IN PLANT SCIENCE 2020; 11:847. [PMID: 32612627 PMCID: PMC7308548 DOI: 10.3389/fpls.2020.00847] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Accepted: 05/26/2020] [Indexed: 05/25/2023]
Abstract
Given that flower size and pigmentation can mediate plant-pollinator interactions, many studies have focused on pollinator-driven selection on these floral traits. However, abiotic factors such as precipitation, temperature, and solar radiation also contribute to geographic variation in floral color, pattern, and size within multiple species. Several studies have described an ecogeographic pattern within species in which high temperature, high ultraviolet (UV) radiation, low precipitation and/or low latitudes are associated with increased floral anthocyanin production, smaller flowers, and/or larger UV-absorbing floral patterns (nectar guides or bullseyes). However, latitude or elevation is often used as a proxy variable to study variation in floral traits associated with a wide range of climatic variables, making the proximate abiotic drivers of variation difficult to identify. In this study, we tested and corroborated several predictions for how the abiotic environment may directly or indirectly shape geographic patterns of floral color, pattern, and size in Clarkia unguiculata (Onagraceae). This study provides the first report of geographic variation in multispectral floral color and pattern in C. unguiculata, while also providing an experimental test of the putative protective role of UV absorption for pollen performance. We quantified geographic variation among greenhouse-raised populations in UV floral pattern size, mean UV petal reflectance, anthocyanin concentration, and petal area in C. unguiculata across its natural range in California and, using 30 year climate normals for each population, we identified climatic and topographic attributes that are correlated with our focal floral traits. In addition, we examined pollen performance under high and low UV light conditions to detect the protective function (if any) of UV floral patterns in this species. Contrary to our expectations, the nectar guide and the proportion of the petal occupied by the UV nectar guide were largest in low solar UV populations. Estimated floral anthocyanin concentration was highest in populations with high solar UV, which does support our predictions. The size of the UV nectar guide did not affect pollen performance in either of the light treatments used in this study. We conclude that, under the conditions examined here, UV-absorbing floral patterns do not serve a direct "pollen protection" function in C. unguiculata. Our results only partially align with expected ecogeographic patterns in these floral traits, highlighting the need for research in a wider range of taxa in order to detect and interpret broad scale patterns of floral color variation.
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Affiliation(s)
- Kristen Peach
- Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, Santa Barbara, CA, United States
| | - Jasen W. Liu
- Population Biology Graduate Group, University of California, Davis, Davis, CA, United States
| | - Susan J. Mazer
- Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, Santa Barbara, CA, United States
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Malagon DA, Roche MD, McElderry RM, Kalisz S. Pollen performance decreases with plant age for outcrosser but not selfer: evidence for cost of male performance. AMERICAN JOURNAL OF BOTANY 2019; 106:1271-1278. [PMID: 31442320 DOI: 10.1002/ajb2.1346] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2019] [Accepted: 06/19/2019] [Indexed: 06/10/2023]
Abstract
PREMISE Declines in reproductive capabilities with increasing age are common across the tree of life. However, in plants, mating system traits have rarely been tested for signs of senescence. Since reproduction is often resource limited, we might expect outcrossing and selfing taxa to allocate these resources differently, especially as a plant ages. Compared with selfers, outcrossers are expected to produce showy, rewarding flowers that attract pollinators and high-quality pollen that can successfully compete for ovules. Yet, this resource-intensive strategy of outcrossers may result in declines in floral allocation and pollen performance metrics, relative to selfers. METHODS To explore age-related changes in reproduction, we measured flower size and pollen germinability over the flowering period for multiple populations of an annual sister species pair, Collinsia linearis (outcrosser) and C. rattanii (selfer), in a growth chamber experiment. RESULTS We found that flower size decreased significantly with age in both species. The outcrosser expressed a significant and dramatic (88%) decline in pollen germinability with age, while the selfer's pollen germinability decline was non-significant and low (17%). CONCLUSIONS Our results support the idea that the higher total cost of reproduction in outcrossers can deplete available resources more rapidly than in selfers, manifesting as a decline in male performance with plant age.
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Affiliation(s)
- Daniel A Malagon
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee, 37996, USA
| | - Morgan D Roche
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee, 37996, USA
| | - Robert M McElderry
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee, 37996, USA
| | - Susan Kalisz
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee, 37996, USA
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Peach K, Mazer SJ. Heteranthery in Clarkia: pollen performance of dimorphic anthers contradicts expectations. AMERICAN JOURNAL OF BOTANY 2019; 106:598-603. [PMID: 30901494 DOI: 10.1002/ajb2.1262] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2018] [Accepted: 01/16/2019] [Indexed: 05/11/2023]
Abstract
PREMISE OF THE STUDY Wild plant species that require the services of pollen-feeding insects for reliable pollination may evolve features that attract and reward their mutualistic partners. Heterantherous species have been proposed to exhibit a "division of labor" whereby "feeding anthers" (which produce pollen that may be consumed by an insect) are distinguished from "reproductive anthers" (which produce pollen more likely to contribute to reproduction). In some heterantherous species, including Clarkia unguiculata (Onagraceae), these two anther types differ with respect to stamen length, anther size, pollen production, and pollen color. METHODS The primary goal of this study was to test one component of the "division of labor" hypothesis by comparing the performance of the pollen produced by each type of anther in C. unguiculata. To achieve this goal, under greenhouse conditions, we hand pollinated and assessed pollen performance (using epifluorescence microscopy) within ~228 flowers. KEY RESULTS The pollen produced by the two anther types differed significantly with respect to both stigma and style penetration. The inner series of anthers produce pollen with higher performance than the outer series of longer, dark red anthers. CONCLUSIONS These findings contradict previous descriptions of the genus, reporting that the inner diminutive series of anthers in Clarkia produce "abortive and nonfunctional" pollen. We outline the future research required to demonstrate the ecological function of heteranthery in this iconic wildflower group.
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Affiliation(s)
- Kristen Peach
- Ecology, Evolution & Marine Biology Department, University of California Santa Barbara, Santa Barbara, California, 93105, USA
| | - Susan J Mazer
- Ecology, Evolution & Marine Biology Department, University of California Santa Barbara, Santa Barbara, California, 93105, USA
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Mazer SJ, Hendrickson BT, Chellew JP, Kim LJ, Liu JW, Shu J, Sharma MV. Divergence in pollen performance between Clarkia sister species with contrasting mating systems supports predictions of sexual selection. Evolution 2018; 72:453-472. [PMID: 29359333 DOI: 10.1111/evo.13429] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2017] [Revised: 01/07/2018] [Accepted: 01/09/2018] [Indexed: 12/22/2022]
Abstract
Animal taxa that differ in the intensity of sperm competition often differ in sperm production or swimming speed, arguably due to sexual selection on postcopulatory male traits affecting siring success. In plants, closely related self- and cross-pollinated taxa similarly differ in the opportunity for sexual selection among male gametophytes after pollination, so traits such as the proportion of pollen on the stigma that rapidly enters the style and mean pollen tube growth rate (PTGR) are predicted to diverge between them. To date, no studies have tested this prediction in multiple plant populations under uniform conditions. We tested for differences in pollen performance in greenhouse-raised populations of two Clarkia sister species: the predominantly outcrossing C. unguiculata and the facultatively self-pollinating C. exilis. Within populations of each taxon, groups of individuals were reciprocally pollinated (n = 1153 pollinations) and their styles examined four hours later. We tested for the effects of species, population, pollen type (self vs. outcross), the number of competing pollen grains, and temperature on pollen performance. Clarkia unguiculata exhibited higher mean PTGR than C. exilis; pollen type had no effect on performance in either taxon. The difference between these species in PTGR is consistent with predictions of sexual selection theory.
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Affiliation(s)
- Susan J Mazer
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, California 93106
| | - Brandon T Hendrickson
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, California 93106
| | - Joseph P Chellew
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, California 93106
| | - Lynn J Kim
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, California 93106
| | - Jasen W Liu
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, California 93106
| | - Jasper Shu
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, California 93106
| | - Manju V Sharma
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, California 93106
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Hove AA, Mazer SJ, Ivey CT. Seed set variation in wild Clarkia populations: teasing apart the effects of seasonal resource depletion, pollen quality, and pollen quantity. Ecol Evol 2016; 6:6524-6536. [PMID: 27777726 PMCID: PMC5058524 DOI: 10.1002/ece3.2372] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Revised: 06/13/2016] [Accepted: 07/11/2016] [Indexed: 12/02/2022] Open
Abstract
In habitats where resource availability declines during the growing season, selection may favor early‐flowering individuals. Under such ephemerally favorable conditions, late‐blooming species (and individuals) may be particularly vulnerable to resource limitation of seed production. In California, a region prone to seasonal drought, members of the annual genus Clarkia are among the last to flower in the spring. We compared pollen limitation (PL) of seed set and outcrossing rates between early‐ and late‐flowering individuals in two mixed‐mating Clarkia taxa to detect whether flowering time is associated with changes in seed set due to resource depletion, PL, or increased selfing. In 2008–2010, we hand‐pollinated one flower on a total of 1855 individual plants either Early (near the onset of flowering) or Late (near the end of flowering) in the flowering season and compared seed set to adjacent, open‐pollinated flowers on the same stem. To assess the contribution of pollen quality to reproduction, we first (2008) used allozymes to estimate outcrossing rates of seeds produced by Early and Late open‐pollinated flowers. Second (2009), we conducted an anther‐removal experiment to estimate self‐pollen deposition. Seed set in Clarkia unguiculata was not pollen‐limited. Clarkia xantiana ssp. xantiana was pollen‐limited in 2008 and 2010, but not 2009. PL did not differ between Early and Late treatments. In both taxa, seed set of Early flowers was greater than Late flowers, but not due to PL in the latter. Reproduction was generally pollinator‐dependent. Most pollen deposition was xenogamous, and outcrossing rates were >0.7 – and similar between Early and Late periods. These results suggest that pollen receipt and pollen quality remain seasonally consistent. By contrast, the resources necessary to provision seeds decline, reducing the fitness benefits associated with resource allocation to ovules.
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Affiliation(s)
- Alisa A Hove
- Biology Department Warren Wilson College PO Box 9000 Asheville NC 28815-6217
| | - Susan J Mazer
- Ecology, Evolution, and Marine Biology Department University of California Santa Barbara CA 93106
| | - Christopher T Ivey
- Department of Biological Sciences California State University Chico Chico CA 95929-0515
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Williams JH, Edwards JA, Ramsey AJ. Economy, efficiency, and the evolution of pollen tube growth rates. AMERICAN JOURNAL OF BOTANY 2016; 103:471-483. [PMID: 26936897 DOI: 10.3732/ajb.1500264] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2015] [Accepted: 10/08/2015] [Indexed: 06/05/2023]
Abstract
PREMISE Pollen tube growth rate (PTGR) is an important aspect of male gametophyte performance because of its central role in the fertilization process. Theory suggests that under intense competition, PTGRs should evolve to be faster, especially if PTGR accurately reflects gametophyte quality. Oddly, we know remarkably little about how effectively the work of tube construction is translated to elongation (growth and growth rate). Here we test the prediction that pollen tubes grow equally efficiently by comparing the scaling of wall production rate (WPR) to PTGR in three water lilies that flower concurrently: Nymphaea odorata, Nuphar advena and Brasenia schreberi. METHODS Single-donor pollinations on flower or carpel pairs were fixed just after pollen germination (time A) and 45 min later (time B). Mean PTGR was calculated as the average increase in tube length over that growth period. Tube circumferences (C) and wall thicknesses (W) were measured at time B. For each donor, WPR = mean (C × W) × mean PTGR. KEY RESULTS Within species, pollen tubes maintained a constant WPR to PTGR ratio, but species had significantly different ratios. N. odorata and N. advena had similar PTGRs, but for any given PTGR, they had the lowest and highest WPRs, respectively. CONCLUSIONS We showed that growth rate efficiencies evolved by changes in the volume of wall material used for growth and in how that material was partitioned between lateral and length dimensions. The economics of pollen tube growth are determined by tube design, which is consequent on trade-offs between efficient growth and other pollen tube functions.
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Affiliation(s)
- Joseph H Williams
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996 USA
| | - Jacob A Edwards
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996 USA
| | - Adam J Ramsey
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996 USA
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Lankinen Å, Smith HG, Andersson S, Madjidian JA. Selection on pollen and pistil traits during pollen competition is affected by both sexual conflict and mixed mating in a self-compatible herb. AMERICAN JOURNAL OF BOTANY 2016; 103:541-552. [PMID: 26542842 DOI: 10.3732/ajb.1500148] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2015] [Accepted: 07/15/2015] [Indexed: 06/05/2023]
Abstract
PREMISE OF THE STUDY Although much attention has focused on the diversity of plant mating systems, only a few studies have considered the joint effects of mating system and sexual conflict in plant evolution. In mixed-mating Collinsia heterophylla, a sexual conflict over timing of stigma receptivity is proposed: pollen with a capacity to induce early onset of stigma receptivity secures paternity for early-arriving pollen (at the expense of reduced maternal seed set), whereas late onset of stigma receptivity mitigates the negative effects of early-arriving pollen. Here we investigated whether selection on pollen and pistil traits involved in sexual conflict is affected by the presence of both outcross- and self-pollen (mixed mating) during pollen competition. METHODS We conducted two-donor crosses at different floral developmental stages to explore male fitness (siring ability) and female fitness (seed set) in relation to male and female identity, pollen and pistil traits, and type of competitor pollen (outcross vs. self). KEY RESULTS Late-fertilizing pollen rather than rapidly growing pollen tubes was most successful in terms of siring success, especially in competition with self-pollen after pollination at early floral stages. Late stigma receptivity increased seed set after early-stage pollinations, in agreement with selection against antagonistic pollen. CONCLUSIONS Selection on pollen and pistil traits in C. heterophylla is affected by both sexual conflict and mixed mating, suggesting the importance of jointly considering these factors in plant evolution.
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Affiliation(s)
- Åsa Lankinen
- Swedish University of Agricultural Sciences, Plant Protection Biology, P.O. Box 102, S-230 53 Alnarp, Sweden Biodiversity, Department of Biology, Lund University, Ecology Building, S-223 62 Lund, Sweden
| | - Henrik G Smith
- Biodiversity, Department of Biology, Lund University, Ecology Building, S-223 62 Lund, Sweden Center for Environmental and Climate Research, Lund University, S-223 62 Lund, Sweden
| | - Stefan Andersson
- Biodiversity, Department of Biology, Lund University, Ecology Building, S-223 62 Lund, Sweden
| | - Josefin A Madjidian
- Biodiversity, Department of Biology, Lund University, Ecology Building, S-223 62 Lund, Sweden
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Hersh E, Madjidian JA, Andersson S, Strandh M, Armbruster WS, Lankinen Å. Sexual antagonism in the pistil varies among populations of a hermaphroditic mixed-mating plant. J Evol Biol 2015; 28:1321-34. [DOI: 10.1111/jeb.12656] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Revised: 04/13/2015] [Accepted: 05/15/2015] [Indexed: 12/01/2022]
Affiliation(s)
- E. Hersh
- Biodiversity; Department of Biology; Lund University; Lund Sweden
| | - J. A. Madjidian
- Biodiversity; Department of Biology; Lund University; Lund Sweden
| | - S. Andersson
- Biodiversity; Department of Biology; Lund University; Lund Sweden
| | - M. Strandh
- Swedish University of Agricultural Sciences; Plant Protection Biology; Alnarp Sweden
| | - W. S. Armbruster
- School of Biological Science; University of Portsmouth; Portsmouth UK
- Institute of Arctic Biology; University of Alaska; Fairbanks AK USA
- Department of Biology; Norwegian University of Science and Technology; Trondheim Norway
| | - Å. Lankinen
- Swedish University of Agricultural Sciences; Plant Protection Biology; Alnarp Sweden
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Lankinen Å, Karlsson Green K. Using theories of sexual selection and sexual conflict to improve our understanding of plant ecology and evolution. AOB PLANTS 2015; 7:plv008. [PMID: 25613227 PMCID: PMC4344479 DOI: 10.1093/aobpla/plv008] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Today it is accepted that the theories of sexual selection and sexual conflict are general and can be applied to both animals and plants. However, potentially due to a controversial history, plant studies investigating sexual selection and sexual conflict are relatively rare. Moreover, these theories and concepts are seldom implemented in research fields investigating related aspects of plant ecology and evolution. Even though these theories are complex, and can be difficult to study, we suggest that several fields in plant biology would benefit from incorporating and testing the impact of selection pressures generated by sexual selection and sexual conflict. Here we give examples of three fields where we believe such incorporation would be particularly fruitful, including (i) mechanisms of pollen-pistil interactions, (ii) mating-system evolution in hermaphrodites and (iii) plant immune responses to pests and pathogens.
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Affiliation(s)
- Åsa Lankinen
- Swedish University of Agricultural Sciences, Plant Protection Biology, PO Box 102, S-230 53 Alnarp, Sweden
| | - Kristina Karlsson Green
- Swedish University of Agricultural Sciences, Plant Protection Biology, PO Box 102, S-230 53 Alnarp, Sweden
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