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Laura F Galloway - One of the best experts on this subject based on the ideXlab platform.
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Populations with greater flexibility in floral traits modify mating system in response to the pollinator environment
Functional Ecology, 2018Co-Authors: Lia Leibman, Matthew H Koski, Anne Rowe, Laura F GallowayAbstract:1. Mixed mating and variation in outcrossing rate among populations of the same species are common. Outcrossing can be affected by pollinator activity and floral traits that facilitate or impede autonomous self-fertilization. However, the relative contribution of pollen limitation and evolved differences in the ability to self fertilize to variation in the mating system is poorly understood and can only be disentangled using an experimental approach. 2. We placed arrays of plants from eight Campanula americana populations that varied in autonomous selfing ability (hereafter "autonomy") in sun and shade habitats to create high- and low-pollination environments. Floral visitors were observed and pollen limitation, Dichogamy, herkogamy, and pollen persistence within the flower were measured. Outcrossing rate was estimated for a subset of the arrays. 3. Pollen limitation was over three-times higher in the shade than the sun due to differences in pollinator visitation. Populations with high levels of autonomy displayed greater pollen persistence and Dichogamy in the more pollen-limited environments than in the high-pollination environments. In these high-autonomy populations, outcrossing rates were tightly associated with pollen limitation, with reduced outcrossing under strong pollen limitation. In contrast, populations with intermediate autonomy levels had less plastic floral traits and their outcrossing rates changed little with pollen limitation.4. Mating system was shaped by both the pollination environment and the magnitude of plasticity in floral traits. The experimental approach used here revealed that plasticity in floral traits provides the ability to adjust mating system in response to limited potential for outcrossing. The lack of plasticity in some populations could explain mismatches between pollinator activity and mating system in natural populations. Finally, flexibility in the mating system may help explain the prevalence of mixed mating
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timing is everything Dichogamy and pollen germinability underlie variation in autonomous selfing among populations
American Journal of Botany, 2018Co-Authors: Matthew H Koski, Kerstin M Niedermaier, Laura F GallowayAbstract:PREMISE OF THE STUDY: The evolution of multiple floral traits often underlies the transition from outcrossing to selfing. Such traits can influence the ability to self, and the timing at which selfing occurs, which in turn affects the costs of selfing. Species that display variation in autonomous selfing provide an opportunity to dissect the phenotypic changes that contribute to variability in the mating system. METHODS: In a common garden, we measured Dichogamy and herkogamy in 24 populations of the protandrous mixed-mating herb Campanula americana, and related these to autonomous fruit set (autonomy). We then measured the timing of self-pollen deposition and fruit production in populations with high and low autonomy, and determined whether pollen germinability across floral development contributes to variation in autonomy. KEY RESULTS: Populations that transitioned more rapidly to female phase displayed elevated autonomous selfing, but herkogamy was unassociated with autonomous selfing. Selfing occurred more rapidly in highly autonomous populations because of greater self-pollen deposition early in female phase. Pollen germinability in low-autonomy populations remained constant across floral development, but in high-autonomy populations it increased after floral anthesis and was highest near the onset of female phase. CONCLUSIONS: Reduced Dichogamy, elevated self-pollen deposition, and higher pollen germination late in male phase contribute to both earlier selfing and greater selfing. These traits vary among populations, likely reflecting past selection on the mating system. While delayed selfing bears fewer fitness costs, the evolution of earlier selfing may be favored if self-pollen availability decreases over floral development.
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do Dichogamy and herkogamy reduce sexual interference in a self incompatible species
Functional Ecology, 2011Co-Authors: Can Dai, Laura F GallowayAbstract:Summary 1. Dichogamy and herkogamy respectively represent the temporal and spatial separation of male and female reproductive functions. They are regarded as mechanisms to avoid selfing, to promote outcrossing and, particularly in self-incompatible plants, to reduce sexual interference. However, little is known about the extent to which these mechanisms reduce sexual interference, and whether this reduction impacts fitness. 2. We studied patterns of Dichogamy and herkogamy, their influence on sexual interference, and the fitness outcome in self-incompatible Passiflora incarnata. We manipulated flowers to be adichogamous or unisexual to evaluate fruit production under increased and decreased sexual interference. 3. Incomplete protandry guaranteed that almost half of the pollen could be successfully exported without interfering with the stigmas, indicating Dichogamy may facilitate male pollination success. We found no difference in pollen deposition between natural and emasculated flowers, suggesting that herkogamy does not decrease self pollination. Increased herkogamy resulted in reduced pollen deposition and lower probability of setting fruits, however, a higher seed number. No difference in female fitness was detected under experimentally increased or decreased sexual interference. 4. Taken together, our results suggest that Dichogamy is mostly driven by the advantage to male fitness and herkogamy is chiefly determined by female fitness. The lack of difference in female fitness under varied levels of sexual interference indicates that male function is more likely to play a role in shaping floral traits that reduce sexual interference.
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Do Dichogamy and herkogamy reduce sexual interference in a self‐incompatible species?
Functional Ecology, 2010Co-Authors: Can Dai, Laura F GallowayAbstract:Summary 1. Dichogamy and herkogamy respectively represent the temporal and spatial separation of male and female reproductive functions. They are regarded as mechanisms to avoid selfing, to promote outcrossing and, particularly in self-incompatible plants, to reduce sexual interference. However, little is known about the extent to which these mechanisms reduce sexual interference, and whether this reduction impacts fitness. 2. We studied patterns of Dichogamy and herkogamy, their influence on sexual interference, and the fitness outcome in self-incompatible Passiflora incarnata. We manipulated flowers to be adichogamous or unisexual to evaluate fruit production under increased and decreased sexual interference. 3. Incomplete protandry guaranteed that almost half of the pollen could be successfully exported without interfering with the stigmas, indicating Dichogamy may facilitate male pollination success. We found no difference in pollen deposition between natural and emasculated flowers, suggesting that herkogamy does not decrease self pollination. Increased herkogamy resulted in reduced pollen deposition and lower probability of setting fruits, however, a higher seed number. No difference in female fitness was detected under experimentally increased or decreased sexual interference. 4. Taken together, our results suggest that Dichogamy is mostly driven by the advantage to male fitness and herkogamy is chiefly determined by female fitness. The lack of difference in female fitness under varied levels of sexual interference indicates that male function is more likely to play a role in shaping floral traits that reduce sexual interference.
Steven D Johnson - One of the best experts on this subject based on the ideXlab platform.
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Floral traits mediate the vulnerability of aloes to pollen theft and inefficient pollination by bees
Annals of botany, 2012Co-Authors: Anna L. Hargreaves, Lawrence D. Harder, Steven D JohnsonAbstract:† Background and Aims Pollen-collecting bees are among the most important pollinators globally, but are also the most common pollen thieves and can significantly reduce plant reproduction. The pollination efficiency of pollen collectors depends on the frequency of their visits to female(-phase) flowers, contact with stigmas and deposition of pollen of sufficient quantity and quality to fertilize ovules. Here we investigate the relative importance of these components, and the hypothesis that floral and inflorescence characteristics mediate the pollination role of pollen collection by bees. † Methods For ten Aloe species that differ extensively in floral and inflorescence traits, we experimentally excluded potential bird pollinators to quantify the contributions of insect visitors to pollen removal, pollen deposition and seed production. We measured corolla width and depth to determine nectar accessibility, and the phenology of anther dehiscence and stigma receptivity to quantify herkogamy and Dichogamy. Further, we compiled all published bird-exclusion studies of aloes, and compared insect pollination success with floral morphology. † Key Results Species varied from exclusively insect pollinated, to exclusively bird pollinated but subject to extensive pollen theft by insects. Nectar inaccessibility and strong Dichogamy inhibited pollination by pollen-collecting bees by discouraging visits to female-phase (i.e. pollenless) flowers. For species with large inflorescences of pollen-rich flowers, pollen collectors successfully deposited pollen, but of such low quality ( probably selfpollen) that they made almost no contribution to seed set. Indeed, considering all published bird-exclusion studies (17 species in total), insect pollination efficiency varied significantly with floral shape. † Conclusions Species-specific floral and inflorescence characteristics, especially nectar accessibility and Dichogamy, control the efficiency of pollen-collecting bees as pollinators of aloes.
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Native pollen thieves reduce the reproductive success of a hermaphroditic plant, Aloe maculata.
Ecology, 2010Co-Authors: Anna L. Hargreaves, Lawrence D. Harder, Steven D JohnsonAbstract:Pollen is unique among floral rewards in functioning as both a carrier of gametes and an attractant and nutritious resource for floral visitors. Animals that collect pollen without pollinating (pollen thieves) could reduce siring success of thieved plants and cause pollen limitation of seed set at the population level; however, such impacts on plant reproduction have not been demonstrated experimentally. To test these effects we added hives of native honey bees (Apis mellifera scutellata) to populations of a primarily bird-pollinated plant, Aloe maculata, in eastern South Africa. In field and aviary trials, bee addition increased pollen removal from anthers but decreased pollen deposition on stigmas, and so reduced both male and female pollination components. Further, total seed production decreased with hive addition in the aviary experiment and in three of four field populations, indicating that population-level pollen theft can also compromise reproductive success. In the field, naturally occurring allodapine bees also seemed to act as pollen thieves, outweighing the effect of honey bee hive addition at one of the four aloe populations. Our results highlight the importance of social bees as pollen thieves, even of plants that have evolved in their presence, and the role of Dichogamy in promoting pollen theft. Given the commonness of both social bees and Dichogamy, pollen theft is likely a much more common influence on floral ecology and evolution than suggested by the sparse literature.
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Consumptive emasculation: the ecological and evolutionary consequences of pollen theft.
Biological reviews of the Cambridge Philosophical Society, 2009Co-Authors: Anna L. Hargreaves, Lawrence D. Harder, Steven D JohnsonAbstract:Many of the diverse animals that consume floral rewards act as efficient pollinators; however, others 'steal' rewards without 'paying' for them by pollinating. In contrast to the extensive studies of the ecological and evolutionary consequences of nectar theft, pollen theft and its implications remain largely neglected, even though it affects plant reproduction more directly. Here we review existing studies of pollen theft and find that: (1) most pollen thieves pollinate other plant species, suggesting that theft generally arises from a mismatch between the flower and thief that precludes pollen deposition, (2) bees are the most commonly documented pollen thieves, and (3) the floral traits that typically facilitate pollen theft involve either spatial or temporal separation of sex function within flowers (herkogamy and Dichogamy, respectively). Given that herkogamy and Dichogamy occur commonly and that bees are globally the most important floral visitors, pollen theft is likely a greatly under-appreciated component of floral ecology and influence on floral evolution. We identify the mechanisms by which pollen theft can affect plant fitness, and review the evidence for theft-induced ecological effects, including pollen limitation. We then explore the consequences of pollen theft for the evolution of floral traits and sexual systems, and conclude by identifying key directions for future research.
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protandry promotes male pollination success in a moth pollinated orchid
Functional Ecology, 2007Co-Authors: Jana Jersakova, Steven D JohnsonAbstract:1. Temporal separation of male and female phases in hermaphrodite flowers (Dichogamy) is proposed to reduce self-pollination, both within and among flowers. Darwin and later workers suggested that protandry (the most common form of Dichogamy, in which the male phase precedes the female phase) should be most effective in reducing geitonogamous (between-flower) self-pollination when pollinators forage upwards from older female-phase flowers to younger male-phase flowers on vertical inflorescences. 2. We tested this hypothesis by manipulating the extent of protandry in artificial inflorescences of the orchid Satyrium longicauda Lindl. and using stained pollen to quantify self-pollination and pollen export. 3. Upper flowers of non-protandrous inflorescences received more self-pollen through geitonogamy than lower flowers, unlike protandrous inflorescences. Protandry reduced absolute levels of self-pollination, as the amount of removed pollen involved in self-pollination was three times greater in non-protandrous than in protandrous inflorescences. This high level of self-pollination reduced the pollen available for export, as the ratio of pollen export to self-pollination declined with increasing self-pollination, indicating the occurrence of pollen discounting. 4. This study represents the first direct measurement of the effects of protandry on the pollination process, and indicates that the evolution of protandry in plants could be driven strongly by the consequences of this trait for male mating success.
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Protandry promotes male pollination success in a moth‐pollinated orchid
Functional Ecology, 2007Co-Authors: Jana Jersakova, Steven D JohnsonAbstract:1. Temporal separation of male and female phases in hermaphrodite flowers (Dichogamy) is proposed to reduce self-pollination, both within and among flowers. Darwin and later workers suggested that protandry (the most common form of Dichogamy, in which the male phase precedes the female phase) should be most effective in reducing geitonogamous (between-flower) self-pollination when pollinators forage upwards from older female-phase flowers to younger male-phase flowers on vertical inflorescences. 2. We tested this hypothesis by manipulating the extent of protandry in artificial inflorescences of the orchid Satyrium longicauda Lindl. and using stained pollen to quantify self-pollination and pollen export. 3. Upper flowers of non-protandrous inflorescences received more self-pollen through geitonogamy than lower flowers, unlike protandrous inflorescences. Protandry reduced absolute levels of self-pollination, as the amount of removed pollen involved in self-pollination was three times greater in non-protandrous than in protandrous inflorescences. This high level of self-pollination reduced the pollen available for export, as the ratio of pollen export to self-pollination declined with increasing self-pollination, indicating the occurrence of pollen discounting. 4. This study represents the first direct measurement of the effects of protandry on the pollination process, and indicates that the evolution of protandry in plants could be driven strongly by the consequences of this trait for male mating success.
You-hao Guo - One of the best experts on this subject based on the ideXlab platform.
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The differential contributions of herkogamy and Dichogamy as mechanisms of avoiding self-interference in four self-incompatible Epimedium species.
Journal of evolutionary biology, 2013Co-Authors: Y. Zou, C.-l. Xiao, Robert Wahiti Gituru, You-hao Guo, Chun-feng YangAbstract:Self-interference is one of the most important selective forces in shaping floral evolution. Herkogamy and Dichogamy both can achieve reductions in the extent of self-interference, but they may have different roles in minimizing self-interference in a single species. We used four self-incompatible Epimedium species to explore the roles of herkogamy and Dichogamy in avoiding self-interference and to test the hypothesis that herkogamy and Dichogamy may be separated and become selected preferentially in the taxa. Two species (E. franchetii and E. mikinorii) expressed strong herkogamy and weak protogyny (aDichogamy), whereas another two species (E. sutchuenense and E. leptorrhizum) expressed slight herkogamy and partial protandry. Field investigations indicated that there was no physical self-interference between male function and female function regarding pollen removal and pollen deposition in all species. Self-pollination (autonomous or facilitated) was greater in species with slight herkogamy than in those with strong herkogamy. Artificial pollination treatments revealed that self-pollination could reduce outcrossed female fertility in all species, and we found evidence that self-interference reduced seed set in E. sutchuenense and E. leptorrhizum in the field, but not in E. franchetii and E. mikinorii. These results indicate that well-developed herkogamy is more effective compared with Dichogamy in avoiding self-interference in the four species. In genus Epimedium, herkogamy instead of Dichogamy should be selected preferentially and evolved as an effective mechanism for avoiding self-interference and might not need to evolve linked with Dichogamy.
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temporal floral sex allocation in protogynous aquilegia yabeana contrasts with protandrous species support for the mating environment hypothesis
Evolution, 2004Co-Authors: Shuangquan Huang, Lulu Tang, You-hao GuoAbstract:We tested one of the predictions of Brunet and Charlesworth (1995) that relative floral sex allocation will vary temporally with the mating environment and that the form of Dichogamy (protandry vs. protogyny) will select for the pattern of variation in male versus female resource allocation. In many hermaphroditic plant species, allocation to female function (ovule number) decreases from early to late flowers within inflorescences as a result of resource limitation or ontogenetic changes. This pattern may obscure the effects of the mating environment and Dichogamy on selection for allocation patterns in protandrous species (male allocation increases regardless). By examining a protogynous species the alternative pattern of temporal variation in resource allocation is predicted, namely that allocation to male function should decrease (or female allocation increase) throughout the flowering sequence. This pattern was observed in protogynous Aquilegia yabeana (Ranunculaceae), in which ovule number per flower remained constant whereas pollen number decreased in sequentially blooming flowers. These observations support the temporal sex allocation hypothesis of Brunet and Charlesworth (1995).
Jian-quan Liu - One of the best experts on this subject based on the ideXlab platform.
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Reproductive ecology of the Qinghai-Tibet Plateau endemic Gentiana straminea (Gentianaceae), a hermaphrodite perennial characterized by herkogamy and Dichogamy
Acta Oecologica, 2005Co-Authors: Yuanwen Duan, Jian-quan LiuAbstract:The combined occurrence of both herkogamy and Dichogamy in a hermaphrodite species has been considered to strongly favour outcrossing. In this study, we investigated in detail the reproductive ecology of Gentiana straminea Maxim. (Gentianaceae), a hermaphrodite perennial endemic to the Qinghai-Tibet Plateau. In a series of observations and experiments over four consecutive years, we examined whether the combination of Dichogamy and herkogamy in individual flowers completely prevents geitonogamous pollen transfer in this species. The mode of floral development clearly indicates that autonomous self-pollination is completely avoided through herkogamy and Dichogamy in individual flowers. This implication was confirmed by the breeding experiments, since no seed was produced when flowers were isolated. However, this gentian proved to be highly self-compatible when geitonogamous selfing was artificially induced. Many flowers opened simultaneously on individual plants, the ratio of male to female phase flowers was close to 2:1 in each inflorescence, at the full anthesis phase, and they were randomly distributed amongst the upper, middle and lower parts of each stem's inflorescence. On average, Bombus sushikini Skorikov, the most frequent visitor and only legitimate pollinator of G. straminea, visited nearly two flowers per inflorescence, and four flowers per plant. Among the pollinators' foraging bouts, the proportions of geitonogamous visits to inflorescences or flowers within an individual plant were 29% and 37%, respectively. Therefore, despite the strict dichogamous and herkogamous characteristics of the individual flowers, geitonogamous selfing might still prevail in G. straininea because of the size of its floral displays and the continuous visiting behavior of B. sushkini. (C) 2005 Elsevier SAS. All rights reserved.
Deborah Charlesworth - One of the best experts on this subject based on the ideXlab platform.
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FLORAL SEX ALLOCATION IN SEQUENTIALLY BLOOMING PLANTS.
Evolution; international journal of organic evolution, 1995Co-Authors: Johanne Brunet, Deborah CharlesworthAbstract:In plants whose flowers develop in a sequence, different flowers may exhibit temporal variation in pollen donation and receipt such that the fitness contributions through male and female functions can vary among flowers. Dichogamy, or directional pollinator movements within inflorescences, can create situations where flowers in different stages in the sequence may differ in the numbers of flowers in the female stage available as potential mates. We present an evolutionarily stable strategy (ESS) analysis of the resource allocations expected in different flowers in hermaphroditic plants when the mating environments vary among flowers. This introduces a modular element into sex-allocation models. Our analysis shows that such variation in the mating environments of flowers can select for differences in sex allocation between flowers. When male and female fertilities are nonlinear functions of the allo- cations, variation in resource availability can also select for variation in sex allocation among flowers. The influence of Dichogamy and pollinator directionality on floral sex allocation is discussed, and the empirical evidence supporting the predictions derived from the model is briefly reviewed. The implications of our results for the evolution of andromonoecy and monoecy are discussed.