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Spencer C H Barrett - One of the best experts on this subject based on the ideXlab platform.
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the biomechanics of pollen release new perspectives on the evolution of Wind Pollination in angiosperms
Biological Reviews of The Cambridge Philosophical Society, 2021Co-Authors: David Timerman, Spencer C H BarrettAbstract:Evolutionary transitions from animal to Wind Pollination have occurred repeatedly during the history of the angiosperms, but the selective mechanisms remain elusive. Here, we propose that knowledge of pollen release biomechanics is critical for understanding the ecological and evolutionary processes underpinning this shift in Pollination mode. Pollen release is the critical first stage of Wind Pollination (anemophily) and stamen properties are therefore likely to be under strong selection early in the transition. We describe current understanding of pollen release biomechanics to provide insights on the phenotypic and ecological drivers of Wind Pollination. Pollen release occurs when detachment forces dominate resistive forces retaining pollen within anthers. Detachment forces can be active or passive depending on whether they require energy input from the environment. Passive release is more widespread in anemophilous species and involves processes driven by steady or unsteady aerodynamic forces or turbulence-induced vibrations that shake pollen from anthers. We review empirical and theoretical studies suggesting that stamen vibration is likely to be a key mechanism of pollen release. The vibration response is governed by morphological and biomechanical properties of stamens, which may undergo divergent selection in the presence or absence of pollinators. Resistive forces have rarely been investigated for pollen within anthers, but are probably sensitive to environmental conditions and depend on flower age, varying systematically between animal- and Wind-pollinated species. Animal and Wind Pollination are traditionally viewed as dichotomous alternatives because they are usually associated with strikingly different Pollination syndromes. But this perspective has diverted attention from subtler, continuously varying traits which mediate the fluid dynamic process of pollen release. Reinterpreting the flower as a biomechanical entity that responds to fluctuating environmental forces may provide a promising way forward. We conclude by identifying several profitable areas for future research to obtain deeper insight into the evolution of Wind Pollination.
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Comparative analysis of pollen release biomechanics in Thalictrum: implications for evolutionary transitions between animal and Wind Pollination
New Phytologist, 2019Co-Authors: David Timerman, Spencer C H BarrettAbstract:: Transitions from animal to Wind Pollination have occurred repeatedly in flowering plants, driven by structural and biomechanical modifications to flowers. But the initial changes promoting Wind Pollination are poorly understood, especially those required to release pollen into airflows - the critical first stage of Wind Pollination. Using a Wind tunnel, we performed a comparative study of pollen release biomechanics in 36 species of animal- and Wind-pollinated Thalictrum. We quantified Pollination syndromes and stamen natural frequency (fn ), a key vibration parameter, to determine if floral traits reliably predicted pollen release probability. We then investigated if pollen release was caused by Wind-induced resonance vibration of stamens. We detected Wind-induced stamen resonance in 91% of species and a strong effect of stamen acceleration on pollen release, inversely driven by fn . However, unlike fn , Pollination syndromes did not reliably predict the probability of pollen release among species. Our results directly link fn to the capacity of stamens to release pollen by Wind and suggest that structural mechanisms reducing fn are likely to be important for initiating transitions from animal to Wind Pollination. Our inability to predict the probability of pollen release based on Pollination syndromes suggests diverse phenotypic trajectories from animal to Wind Pollination.
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divergent selection on the biomechanical properties of stamens under Wind and insect Pollination
Proceedings of The Royal Society B: Biological Sciences, 2018Co-Authors: David Timerman, Spencer C H BarrettAbstract:Wind Pollination has evolved from insect Pollination in numerous angiosperm lineages and is associated with a characteristic syndrome of morphological traits. The traits initiating transitions to Wind Pollination and the ecological drivers involved are poorly understood. Here, we examine this problem in Thalictrum pubescens, an ambophilous (insect and Wind Pollination) species that probably represents a transitional state in the evolution of Wind Pollination. We investigated Wind-induced pollen release by forced harmonic motion by measuring stamen natural frequency ( fn), a key vibration parameter, and its variability among nine populations. We assessed the repeatability of fn over consecutive growing seasons, the effect of this parameter on pollen release in a Wind tunnel, and male reproductive success in the field using experimental manipulation of the presence or absence of pollinators. We found significant differences among populations and high repeatability within genotypes in fn. The Wind tunnel assay revealed a strong negative correlation between fn and pollen release. Siring success was greatest for plants with lower fn when pollinators were absent, but this advantage diminished when pollinators were present. Our biomechanical analysis of the Wind-flower interface has identified fn as a key trait for understanding early stages in the transition from insect to Wind Pollination.
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the evolution of ovule number and flower size in Wind pollinated plants
The American Naturalist, 2011Co-Authors: Jannice Friedman, Spencer C H BarrettAbstract:AbstractIn angiosperms, ovules are “packaged” within individual flowers, and an optimal strategy should occur depending on Pollination and resource conditions. In animal-pollinated species, wide variation in ovule number per flower occurs, and this contrasts with Wind-pollinated plants, where most species possess uniovulate flowers. This pattern is usually explained as an adaptive response to low pollen receipt in Wind-pollinated species. Here, we develop a phenotypic model for the evolution of ovule number per flower that incorporates the aerodynamics of pollen capture and a fixed resource pool for provisioning of flowers, ovules, and seeds. Our results challenge the prevailing explanation for the association between uniovulate flowers and Wind Pollination. We demonstrate that when flowers are small and inexpensive, as they are in Wind-pollinated species, ovule number should be minimized and lower than the average number of pollen tubes per style, even under stochastic Pollination and fertilization regim...
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Wind of change new insights on the ecology and evolution of Pollination and mating in Wind pollinated plants
Annals of Botany, 2009Co-Authors: Jannice Friedman, Spencer C H BarrettAbstract:†Background The rich literature that characterizes the field of Pollination biology has focused largely on animalpollinated plants. At least 10 % of angiosperms are Wind pollinated, and this mode of Pollination has evolved on multiple occasions among unrelated lineages, and hence this discrepancy in research interest is surprising. Here, the evolution and functional ecology of Pollination and mating in Wind-pollinated plants are discussed, a theoretical framework for modelling the selection of Wind Pollination is outlined, and pollen capture and the occurrence of pollen limitation in diverse Wind-pollinated herbs are investigated experimentally. †Scope and Conclusions Wind Pollination may commonly evolve to provide reproductive assurance when pollinators are scarce. Evidence is presented that pollen limitation in Wind-pollinated plants may not be as common as it is in animal-pollinated species. The studies of pollen capture in Wind-pollinated herbs demonstrate that pollen transfer efficiency is not substantially lower than in animal-pollinated plants as is often assumed. These findings challenge the explanation that the evolution of few ovules in Wind-pollinated flowers is associated with low pollen loads. Floral and inflorescence architecture is crucial to Pollination and mating because of the aerodynamics of Wind Pollination. Evidence is provided for the importance of plant height, floral position, and stamen and stigma characteristics in promoting effective pollen dispersal and capture. Finally, it is proposed that geitonogamous selfing may alleviate pollen limitation in many Wind-pollinated plants with unisexual flowers.
Stephen G Weller - One of the best experts on this subject based on the ideXlab platform.
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asymmetrical gene flow in a hybrid zone of hawaiian schiedea caryophyllaceae species with contrasting mating systems
PLOS ONE, 2011Co-Authors: Lisa E Wallace, Stephen G Weller, Ann K Sakai, Theresa M Culley, Ashley Kuenzi, Tilottama Roy, Warren L Wagner, Molly NepokroeffAbstract:Asymmetrical gene flow, which has frequently been documented in naturally occurring hybrid zones, can result from various genetic and demographic factors. Understanding these factors is important for determining the ecological conditions that permitted hybridization and the evolutionary potential inherent in hybrids. Here, we characterized morphological, nuclear, and chloroplast variation in a putative hybrid zone between Schiedea menziesii and S. salicaria, endemic Hawaiian species with contrasting breeding systems. Schiedea menziesii is hermaphroditic with moderate selfing; S. salicaria is gynodioecious and Wind-pollinated, with partially selfing hermaphrodites and largely outcrossed females. We tested three hypotheses: 1) putative hybrids were derived from natural crosses between S. menziesii and S. salicaria, 2) gene flow via pollen is unidirectional from S. salicaria to S. menziesii and 3) in the hybrid zone, traits associated with Wind Pollination would be favored as a result of pollen-swamping by S. salicaria. Schiedea menziesii and S. salicaria have distinct morphologies and chloroplast genomes but are less differentiated at the nuclear loci. Hybrids are most similar to S. menziesii at chloroplast loci, exhibit nuclear allele frequencies in common with both parental species, and resemble S. salicaria in pollen production and pollen size, traits important to Wind Pollination. Additionally, unlike S. menziesii, the hybrid zone contains many females, suggesting that the nuclear gene responsible for male sterility in S. salicaria has been transferred to hybrid plants. Continued selection of nuclear genes in the hybrid zone may result in a population that resembles S. salicaria, but retains chloroplast lineage(s) of S. menziesii.
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predicting the pathway to Wind Pollination heritabilities and genetic correlations of inflorescence traits associated with Wind Pollination in schiedea salicaria caryophyllaceae
Journal of Evolutionary Biology, 2006Co-Authors: Stephen G Weller, Ann K Sakai, Theresa M Culley, Diane R Campbell, Amy K DunbarwallisAbstract:The transition from biotic to abiotic Pollination was investigated using Schiedea, a genus exhibiting a remarkable diversity of inflorescence architecture associated with Pollination biology. Heritabilities and genetic correlations of inflorescence traits were estimated in gynodioecious Schiedea salicaria (Caryophyllaceae), a species that has likely undergone a recent transition to Wind-Pollination. Using a partial diallel crossing design, significant narrow-sense heritabilities were detected for inflorescence condensation (h2 = 0.56 to 0.68 in the two sexes) and other traits related to the extent of Wind Pollination in Schiedea species. Heritabilities were generally higher in hermaphrodites than in females. Strong genetic correlations may constrain the evolution of some inflorescence traits that facilitate Wind Pollination, such as simultaneous shortening of inflorescence length and elongation of the subtending internode. The presence of significant narrow-sense heritabilities for traits associated with Wind Pollination suggests, however, that selection for more effective Wind Pollination in the Windy, pollinator-limited environments where S. salicaria grows could lead to the evolution of the highly condensed inflorescences characteristic of other Wind-pollinated species of Schiedea.
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Wind Pollination sexual dimorphism and changes in floral traits of schiedea caryophyllaceae
American Journal of Botany, 2005Co-Authors: Annette M Golonka, Ann K Sakai, Stephen G WellerAbstract:Both changes in sex allocation and Pollination mode may promote the separation of sexes in plant populations. Simultaneous evolution of Wind Pollination and dimorphism has occurred in Schiedea, where species with different female frequencies provide an opportunity to observe the effect of Wind Pollination on sex allocation and floral morphology. Differences among species in the ratio of anther to ovary volume were not the result of sex allocation trade-offs, but instead resulted from production of vestigial stamens in females; there were no changes in ovary volume in males and hermaphrodites (MH) of dimorphic species. Relative to hermaphroditic species, dimorphic species had more condensed inflorescences, a pattern often associated with Wind Pollination. Within dimorphic species, MH had longer filament lengths than females, and females had longer stigmas than MHs. These traits are characteristic of Wind Pollination, but there was no relationship between the degree of sexual dimorphism and female frequency. Ovary volume and ovule number and size had positive phenotypic correlations between females and MH of dimorphic species, making sex specialization more difficult. In dimorphic Schiedea species, selection for Wind Pollination may have a greater effect on floral traits than trade-offs in allocation between male and female function.
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the evolution of Wind Pollination in angiosperms
Trends in Ecology and Evolution, 2002Co-Authors: Theresa M Culley, Stephen G Weller, Ann K SakaiAbstract:Wind Pollination (anemophily) of angiosperms probably evolved from insect Pollination (entomophily) in response to pollinator limitation and changes in the abiotic environment. Recent evidence suggests that ambophily (a combination of both Wind and insect Pollination) might be more common than was previously presumed and could represent either a stable or transitional state. We review factors favoring the evolution of Wind Pollination and analyse the extent of specialization towards such Pollination. Phylogenetic analyses suggest that anemophily is more likely to evolve in groups with small, simple flowers and dry pollen. Wind-pollinated plants appear to have a bimodal distribution in selfing rates, but further studies recognizing the possibility of a combination of Wind and animal Pollination within taxa are needed to clarify this relationship.
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dioecy and the evolution of Pollination systems in schiedea and alsinidendron caryophyllaceae alsinoideae in the hawaiian islands
American Journal of Botany, 1998Co-Authors: Stephen G Weller, Ann K Sakai, Annette M Golonka, Anne E Rankin, Brenda Kutcher, Karen E AshbyAbstract:The transition from biotic to Wind Pollination and the consequencesof this transition for the evolution of dioecious breeding systems wereinvestigated in Schiedea and Alsinidendron(Caryophyllaceae: Alsinoideae), genera endemic to the Hawaiian Islands. The potential for Wind Pollination was studied for five species ofSchiedea using a Wind tunnel. Morphological correlates of WindPollination for these species were then used to infer the presence orabsence of Wind Pollination in the remaining Schiedea species. Hermaphroditic Alsinidendron and Schiedea species,which occur in mesic to wet forests, or less commonly in dry habitats,show little or no indication of Wind Pollination. These species had lowpollen:ovule ratios, large relative pollen size, diffuse inflorescences,substantial nectar production in several cases, and appear to bebiotically pollinated or autogamous. Sexually dimorphic species, whichall occur in dry habitats, are Wind pollinated, based on Wind tunnelresults or morphological adaptations indicating the potential for WindPollination. These adaptations include high pollen:ovule ratios, smallpollen size, moderately to highly condensed inflorescences, and reducednectaries and nectar production. Shifts to Wind Pollination anddimorphism are strongly correlated in Schiedea, suggesting theclose functional relationship of the twophenomena.
Steven D Johnson - One of the best experts on this subject based on the ideXlab platform.
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floral trait evolution associated with shifts between insect and Wind Pollination in the dioecious genus leucadendron proteaceae
Evolution, 2016Co-Authors: Megan R Welsford, J J Midgley, Nina Hobbhahn, Steven D JohnsonAbstract:Transitions between animal and Wind Pollination have occurred in many lineages and have been linked to various floral modifications, but these have seldom been assessed in a phylogenetic framework. In the dioecious genus Leucadendron (Proteaceae), transitions from insect to Wind Pollination have occurred at least four times. Using analyses that controlled for relatedness among Leucadendron species, we investigated how these transitions shaped the evolution of floral structural and signaling traits, including the degree of sexual dimorphism in these traits. Pollen grains of Wind-pollinated species were found to be smaller, more numerous, and dispersed more efficiently in Wind than were those of insect-pollinated species. Wind-pollinated species also exhibited a reduction in spectral contrast between showy subtending leaves and background foliage, reduced volatile emissions, and a greater degree of sexual dimorphism in color and scent. Uniovulate flowers and inflorescence condensation are conserved ancestral features in Leucadendron and likely served as exaptations in shifts to Wind Pollination. These results offer insights into the key modifications of male and female floral traits involved in transitions between insect and Wind Pollination.
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experimental evaluation of insect Pollination versus Wind Pollination in leucadendron proteaceae
International Journal of Plant Sciences, 2014Co-Authors: Megan R Welsford, J J Midgley, Steven D JohnsonAbstract:Premise of research. Evolutionary transitions from insect to Wind Pollination are thought to have occurred many times during the angiosperm radiation. On the basis of floral features, several such transitions have been postulated for Leucadendron (Proteaceae), a dioecious genus of 96 taxa confined almost entirely to the Cape Floristic Region. To confirm whether these transitions took place, we carried out experimental tests for Wind Pollination and sampled insect flower visitors in 15 Leucadendron species, representing six clades in the genus.Methodology. In three clades in which an insect-Wind shift has been inferred, we sampled species with traits suggestive of either Wind or insect Pollination. Plants were bagged with fine-mesh exclusion bags that excluded insects but allowed the passage of airborne pollen. Insects visiting female inflorescences were collected for identification and analysis of their pollen loads.Pivotal results. We found that insect exclusion had little effect on seed set of five spec...
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Transition from Wind Pollination to insect Pollination in sedges: experimental evidence and functional traits.
The New phytologist, 2011Co-Authors: Peter D. Wragg, Steven D JohnsonAbstract:Transitions from Wind Pollination to insect Pollination were pivotal to the radiation of land plants, yet only a handful are known and the trait shifts required are poorly understood. We tested the hypothesis that a transition to insect Pollination took place in the ancestrally Wind-pollinated sedges (Cyperaceae) and that floral traits modified during this transition have functional significance. We paired putatively insect-pollinated Cyperus obtusiflorus and Cyperus sphaerocephalus with related, co-flowering, co-occurring Wind-pollinated species, and compared pairs in terms of Pollination mode and functional roles of floral traits. Experimentally excluding insects reduced seed set by 56-89% in putatively insect-pollinated species but not in intermingled Wind-pollinated species. The pollen of putatively insect-pollinated species was less motile in a Wind tunnel than that of Wind-pollinated species. Bees, beetles and flies preferred inflorescences, and color-matched white or yellow models, of putatively insect-pollinated species over inflorescences, or color-matched brown models, of Wind-pollinated species. Floral scents of putatively insect-pollinated species were chemically consistent with those of other insect-pollinated plants, and attracted pollinators; Wind-pollinated species were unscented. These results show that a transition from Wind Pollination to insect Pollination occurred in sedges and shed new light on the function of traits involved in this important transition.
Ann K Sakai - One of the best experts on this subject based on the ideXlab platform.
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asymmetrical gene flow in a hybrid zone of hawaiian schiedea caryophyllaceae species with contrasting mating systems
PLOS ONE, 2011Co-Authors: Lisa E Wallace, Stephen G Weller, Ann K Sakai, Theresa M Culley, Ashley Kuenzi, Tilottama Roy, Warren L Wagner, Molly NepokroeffAbstract:Asymmetrical gene flow, which has frequently been documented in naturally occurring hybrid zones, can result from various genetic and demographic factors. Understanding these factors is important for determining the ecological conditions that permitted hybridization and the evolutionary potential inherent in hybrids. Here, we characterized morphological, nuclear, and chloroplast variation in a putative hybrid zone between Schiedea menziesii and S. salicaria, endemic Hawaiian species with contrasting breeding systems. Schiedea menziesii is hermaphroditic with moderate selfing; S. salicaria is gynodioecious and Wind-pollinated, with partially selfing hermaphrodites and largely outcrossed females. We tested three hypotheses: 1) putative hybrids were derived from natural crosses between S. menziesii and S. salicaria, 2) gene flow via pollen is unidirectional from S. salicaria to S. menziesii and 3) in the hybrid zone, traits associated with Wind Pollination would be favored as a result of pollen-swamping by S. salicaria. Schiedea menziesii and S. salicaria have distinct morphologies and chloroplast genomes but are less differentiated at the nuclear loci. Hybrids are most similar to S. menziesii at chloroplast loci, exhibit nuclear allele frequencies in common with both parental species, and resemble S. salicaria in pollen production and pollen size, traits important to Wind Pollination. Additionally, unlike S. menziesii, the hybrid zone contains many females, suggesting that the nuclear gene responsible for male sterility in S. salicaria has been transferred to hybrid plants. Continued selection of nuclear genes in the hybrid zone may result in a population that resembles S. salicaria, but retains chloroplast lineage(s) of S. menziesii.
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predicting the pathway to Wind Pollination heritabilities and genetic correlations of inflorescence traits associated with Wind Pollination in schiedea salicaria caryophyllaceae
Journal of Evolutionary Biology, 2006Co-Authors: Stephen G Weller, Ann K Sakai, Theresa M Culley, Diane R Campbell, Amy K DunbarwallisAbstract:The transition from biotic to abiotic Pollination was investigated using Schiedea, a genus exhibiting a remarkable diversity of inflorescence architecture associated with Pollination biology. Heritabilities and genetic correlations of inflorescence traits were estimated in gynodioecious Schiedea salicaria (Caryophyllaceae), a species that has likely undergone a recent transition to Wind-Pollination. Using a partial diallel crossing design, significant narrow-sense heritabilities were detected for inflorescence condensation (h2 = 0.56 to 0.68 in the two sexes) and other traits related to the extent of Wind Pollination in Schiedea species. Heritabilities were generally higher in hermaphrodites than in females. Strong genetic correlations may constrain the evolution of some inflorescence traits that facilitate Wind Pollination, such as simultaneous shortening of inflorescence length and elongation of the subtending internode. The presence of significant narrow-sense heritabilities for traits associated with Wind Pollination suggests, however, that selection for more effective Wind Pollination in the Windy, pollinator-limited environments where S. salicaria grows could lead to the evolution of the highly condensed inflorescences characteristic of other Wind-pollinated species of Schiedea.
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Wind Pollination sexual dimorphism and changes in floral traits of schiedea caryophyllaceae
American Journal of Botany, 2005Co-Authors: Annette M Golonka, Ann K Sakai, Stephen G WellerAbstract:Both changes in sex allocation and Pollination mode may promote the separation of sexes in plant populations. Simultaneous evolution of Wind Pollination and dimorphism has occurred in Schiedea, where species with different female frequencies provide an opportunity to observe the effect of Wind Pollination on sex allocation and floral morphology. Differences among species in the ratio of anther to ovary volume were not the result of sex allocation trade-offs, but instead resulted from production of vestigial stamens in females; there were no changes in ovary volume in males and hermaphrodites (MH) of dimorphic species. Relative to hermaphroditic species, dimorphic species had more condensed inflorescences, a pattern often associated with Wind Pollination. Within dimorphic species, MH had longer filament lengths than females, and females had longer stigmas than MHs. These traits are characteristic of Wind Pollination, but there was no relationship between the degree of sexual dimorphism and female frequency. Ovary volume and ovule number and size had positive phenotypic correlations between females and MH of dimorphic species, making sex specialization more difficult. In dimorphic Schiedea species, selection for Wind Pollination may have a greater effect on floral traits than trade-offs in allocation between male and female function.
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the evolution of Wind Pollination in angiosperms
Trends in Ecology and Evolution, 2002Co-Authors: Theresa M Culley, Stephen G Weller, Ann K SakaiAbstract:Wind Pollination (anemophily) of angiosperms probably evolved from insect Pollination (entomophily) in response to pollinator limitation and changes in the abiotic environment. Recent evidence suggests that ambophily (a combination of both Wind and insect Pollination) might be more common than was previously presumed and could represent either a stable or transitional state. We review factors favoring the evolution of Wind Pollination and analyse the extent of specialization towards such Pollination. Phylogenetic analyses suggest that anemophily is more likely to evolve in groups with small, simple flowers and dry pollen. Wind-pollinated plants appear to have a bimodal distribution in selfing rates, but further studies recognizing the possibility of a combination of Wind and animal Pollination within taxa are needed to clarify this relationship.
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dioecy and the evolution of Pollination systems in schiedea and alsinidendron caryophyllaceae alsinoideae in the hawaiian islands
American Journal of Botany, 1998Co-Authors: Stephen G Weller, Ann K Sakai, Annette M Golonka, Anne E Rankin, Brenda Kutcher, Karen E AshbyAbstract:The transition from biotic to Wind Pollination and the consequencesof this transition for the evolution of dioecious breeding systems wereinvestigated in Schiedea and Alsinidendron(Caryophyllaceae: Alsinoideae), genera endemic to the Hawaiian Islands. The potential for Wind Pollination was studied for five species ofSchiedea using a Wind tunnel. Morphological correlates of WindPollination for these species were then used to infer the presence orabsence of Wind Pollination in the remaining Schiedea species. Hermaphroditic Alsinidendron and Schiedea species,which occur in mesic to wet forests, or less commonly in dry habitats,show little or no indication of Wind Pollination. These species had lowpollen:ovule ratios, large relative pollen size, diffuse inflorescences,substantial nectar production in several cases, and appear to bebiotically pollinated or autogamous. Sexually dimorphic species, whichall occur in dry habitats, are Wind pollinated, based on Wind tunnelresults or morphological adaptations indicating the potential for WindPollination. These adaptations include high pollen:ovule ratios, smallpollen size, moderately to highly condensed inflorescences, and reducednectaries and nectar production. Shifts to Wind Pollination anddimorphism are strongly correlated in Schiedea, suggesting theclose functional relationship of the twophenomena.
Jannice Friedman - One of the best experts on this subject based on the ideXlab platform.
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the evolution of ovule number and flower size in Wind pollinated plants
The American Naturalist, 2011Co-Authors: Jannice Friedman, Spencer C H BarrettAbstract:AbstractIn angiosperms, ovules are “packaged” within individual flowers, and an optimal strategy should occur depending on Pollination and resource conditions. In animal-pollinated species, wide variation in ovule number per flower occurs, and this contrasts with Wind-pollinated plants, where most species possess uniovulate flowers. This pattern is usually explained as an adaptive response to low pollen receipt in Wind-pollinated species. Here, we develop a phenotypic model for the evolution of ovule number per flower that incorporates the aerodynamics of pollen capture and a fixed resource pool for provisioning of flowers, ovules, and seeds. Our results challenge the prevailing explanation for the association between uniovulate flowers and Wind Pollination. We demonstrate that when flowers are small and inexpensive, as they are in Wind-pollinated species, ovule number should be minimized and lower than the average number of pollen tubes per style, even under stochastic Pollination and fertilization regim...
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Wind of change new insights on the ecology and evolution of Pollination and mating in Wind pollinated plants
Annals of Botany, 2009Co-Authors: Jannice Friedman, Spencer C H BarrettAbstract:†Background The rich literature that characterizes the field of Pollination biology has focused largely on animalpollinated plants. At least 10 % of angiosperms are Wind pollinated, and this mode of Pollination has evolved on multiple occasions among unrelated lineages, and hence this discrepancy in research interest is surprising. Here, the evolution and functional ecology of Pollination and mating in Wind-pollinated plants are discussed, a theoretical framework for modelling the selection of Wind Pollination is outlined, and pollen capture and the occurrence of pollen limitation in diverse Wind-pollinated herbs are investigated experimentally. †Scope and Conclusions Wind Pollination may commonly evolve to provide reproductive assurance when pollinators are scarce. Evidence is presented that pollen limitation in Wind-pollinated plants may not be as common as it is in animal-pollinated species. The studies of pollen capture in Wind-pollinated herbs demonstrate that pollen transfer efficiency is not substantially lower than in animal-pollinated plants as is often assumed. These findings challenge the explanation that the evolution of few ovules in Wind-pollinated flowers is associated with low pollen loads. Floral and inflorescence architecture is crucial to Pollination and mating because of the aerodynamics of Wind Pollination. Evidence is provided for the importance of plant height, floral position, and stamen and stigma characteristics in promoting effective pollen dispersal and capture. Finally, it is proposed that geitonogamous selfing may alleviate pollen limitation in many Wind-pollinated plants with unisexual flowers.
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a phylogenetic analysis of the evolution of Wind Pollination in the angiosperms
International Journal of Plant Sciences, 2008Co-Authors: Jannice Friedman, Spencer C H BarrettAbstract:Wind Pollination is predominantly a derived condition in angiosperms and is thought to evolve in response to ecological conditions that render animal Pollination less advantageous. However, the specific ecological and evolutionary mechanisms responsible for transitions from animal to Wind Pollination are poorly understood in comparison with other major reproductive transitions in angiosperms, including the evolution of selfing from outcrossing and dioecy from hermaphroditism. To investigate correlations between Wind Pollination and a range of characters including habitat type, sexual system, floral display size, floral showiness, and ovule number, we used a large-scale molecular phylogeny of the angiosperms and maximum likelihood methods to infer historical patterns of evolution. This approach enabled us to detect correlated evolution and the order of trait acquisition between Pollination mode and each of nine characters. Log likelihood ratio tests supported a model of correlated evolution for Wind Pollination and habitat type, floral sexuality, sexual system, flower size, flower showiness, presence versus absence of nectar, and ovule number. In contrast, Wind Pollination and geographical distribution and number of flowers per inflorescence evolve independently. We found that in Wind-pollinated taxa, nectar is lost more often and ovule number is reduced to one. We also found that Wind Pollination evolves more frequently in lineages already possessing unisexual flowers and/or unisexual plants. An understanding of the ecological and life-history context in which Wind Pollination originates is fundamental to further investigation of the microevolutionary forces causing transitions from animal to Wind Pollination.
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Inflorescence architecture and Wind Pollination in six grass species
Functional Ecology, 2004Co-Authors: Jannice Friedman, Lawrence D. HarderAbstract:Summary 1. Inflorescence architecture and floral morphology vary extensively within the Poaceae, but the functional significance of this variation remains largely unknown. As grasses are Wind-pollinated, their inflorescence diversity probably reflects alternate solutions to manipulating airstreams to enhance pollen export and import. We tested this hypothesis with two field experiments that contrasted pollen removal and receipt by compact and diffuse inflorescences. 2. In the ‘aggregation’ experiment, we tied together panicle branches of two species with diffuse inflorescences, creating more compact inflorescences. Aggregation reduced pollen removal from both species, probably by increasing boundary-layer thickness. The effects of inflorescence aggregation differed between the two species in a manner that is consistent with pollen-size differences, which could affect the ability of pollen grains to pass through the thickened boundary layer around stigmas. 3. The ‘staking’ experiment constrained inflorescence motion and revealed that culm characteristics contribute to the interaction between grass inflorescences and airstreams. In particular, inflorescence oscillation principally serves pollen removal for species with compact inflorescences, but is of primary importance in pollen receipt for species with diffuse architectures. 4. These results suggest that inflorescence architecture interacts with Wind in a complex manner to facilitate Pollination and supports the hypothesis that the extensive diversity of inflorescence architecture within the Poaceae represents evolutionary solutions to the physical constraints of Wind Pollination.
