The Experts below are selected from a list of 5591523 Experts worldwide ranked by ideXlab platform
Steven D Johnson - One of the best experts on this subject based on the ideXlab platform.
-
Seed production in a threatened Aloe is not affected by bird exclusion or population size
Plant Ecology, 2008Co-Authors: Amy-leigh Wilson, David Ward, Mark Brown, Steven D JohnsonAbstract:Small populations of many plant species have been shown to exhibit ecological Allee effects. These effects are expected to be pronounced in plants which are obligate outcrossers and rely on pollinators which forage preferentially in larger populations with greater nectar availability. We examined the breeding and pollination systems, level of pollen limitation and seed production in populations of a threatened “ornithophilous” species, Aloe pruinosa . Experimental hand-pollinations showed that A. pruinosa is genetically self-incompatible and thus an obligate outcrosser. Experimental exclusion of birds from inflorescences did not affect seed production, suggesting that insects are effective pollinators. Supplemental hand-pollinations in several populations showed that seed production in A. pruinosa is not pollen limited. Further, there were no significant relationships between population size and any measure of reproductive success in this Aloe species. Small populations of A. pruinosa are thus viable in terms of pollination processes and should be protected from more direct threats, such as habitat alteration.
-
Is Eucalyptus Cryptically Self-incompatible?
Annals of Botany, 2007Co-Authors: Tasmien N. Horsley, Steven D JohnsonAbstract:†Background and Aims The probability that seeds will be fertilized from self- versus cross-pollen depends strongly on whether plants have self-incompatibility systems, and how these systems influence the fate of pollen tubes. †Methods In this study of breeding systems in Eucalyptus urophylla and Eucalyptus grandis, epifluorescence microscopy was used to study pollen tube growth in styles following self- and cross-pollinations. †Key Results Pollen tubes from self-pollen took significantly longer than those from cross-pollen to grow to the base of the style in both E. urophylla (120 h vs. 96 h) and E. grandis (96 h vs. 72 h). In addition, both species exhibited reduced seed yields following Self-Pollination compared with cross-pollination. †Conclusions The present observations suggest that, in addition to a late-acting self-incompatibility barrier, cryptic self-incompatibility could be a mechanism responsible for the preferential out-crossing system in these two eucalypt species.
-
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.
-
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.
Jana Jersakova - One of the best experts on this subject based on the ideXlab platform.
-
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.
-
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.
Spencer C H Barrett - One of the best experts on this subject based on the ideXlab platform.
-
Experimental insights on the function of ancillary pollen and stigma polymorphisms in plants with heteromorphic incompatibility.
Evolution, 2016Co-Authors: Joana Costa, Silvia Castro, Joao Loureiro, Spencer C H BarrettAbstract:Most heterostylous plants possess a reciprocal arrangement of stigmas and anthers (reciprocal herkogamy), heteromorphic self-incompatibility and ancillary polymorphisms of pollen and stigmas. The topographical complementarity hypothesis proposes that ancillary polymorphisms function in the rejection of incompatible pollen thus promoting disassortative pollination. Here, we test this hypothesis by investigating patterns of pollen transfer and capture in populations of dimorphic Armeria maritima and A. pubigera and distylous Limonium vulgare (Plumbaginaceae), and by studying pollen adherence and germination patterns in A. maritima following controlled hand-pollinations. Armeria lacks reciprocal herkogamy allowing the evaluation of the extent to which ancillary polymorphisms affect the composition of pollen loads. We compared the amounts of compatible and incompatible pollen on stigmas in natural populations and calculated the proficiencies of pollen transfer for each mating type. We detected disassortative pollination in each species, and mating types did not differ in compatible pollen capture, although cob stigmas captured more incompatible pollen. Controlled hand-pollinations revealed the failure of incompatible pollen to adhere and germinate on stigmas. Our results provided evidence that, while structural in nature, pollen-stigma dimorphisms are tightly associated with heteromorphic incompatibility and likely function to promote disassortative pollination in the absence of reciprocal herkogamy. This article is protected by copyright. All rights reserved
-
the natural history of pollination and mating in bird pollinated babiana iridaceae
Annals of Botany, 2012Co-Authors: Caroli De Waal, Bruce Anderson, Spencer C H BarrettAbstract:BACKGROUND AND AIMS Floral variation, pollination biology and mating patterns were investigated in sunbird-pollinated Babiana (Iridaceae) species endemic to the Western Cape of South Africa. The group includes several taxa with specialized bird perches and it has been proposed that these function to promote cross-pollination. METHODS Pollinator observations were conducted in 12 populations of five taxa (B. ringens subspp. ringens, australis, B. hirsuta, B. avicularis, B. carminea) and geographic variation in morphological traits investigated in the widespread B. ringens. Experimental pollinations were used to determine the compatibility status, facility for autonomous Self-Pollination and intensity of pollen limitation in six populations of four taxa. Allozyme markers were employed to investigate mating patterns in four populations of three species. KEY RESULTS Sunbirds were the primary pollinators of the five Babiana taxa investigated. Correlated geographical variation in perch size, flower size and stigma-anther separation was evident among B. ringens populations. Experimental pollinations demonstrated that B. ringens and B. avicularis were self-compatible with variation in levels of autonomous Self-Pollination and weak or no pollen limitation of seed set. In contrast, B. hirsuta was self-incompatible and chronically pollen limited. Estimates of outcrossing rate indicated mixed mating with substantial self-fertilization in all species investigated. CONCLUSIONS Despite the possession of specialized bird perches in B. ringens and B. avicularis, these structures do not prevent considerable selfing from occurring, probably as a result of autonomous Self-Pollination. In eastern populations of B. ringens, smaller flowers and reduced herkogamy appear to be associated with a shift to predominant selfing. Relaxed selection on perch function due to increased selfing may explain the increased incidence of apical flowers in some populations.
-
reproductive consequences of interactions between clonal growth and sexual reproduction in nymphoides peltata a distylous aquatic plant
New Phytologist, 2004Co-Authors: Yong Wang, Qingfeng Wang, Youhao Guo, Spencer C H BarrettAbstract:Distyly is a sexual polymorphism in which plant populations contain two floral morphs differing in morphology and physiology. The dimorphism serves to promote animal-mediated cross-pollination between the floral morphs. Clonal propagation can interfere with the functioning of distyly by compromising intermorph pollinations, resulting in reduced fertility. Here, we investigate the relations between clonal growth and sexual reproduction in the aquatic macrophyte Nymphoides peltata (Menyanthaceae). Surveys of morph representation in 30 populations from five regions of China revealed that most populations exhibited strongly biased morph ratios and 30% contained a single floral morph. Experimental pollinations indicate that N. peltata possesses a strong dimorphic incompatibility system preventing self and intramorph fertilizations. An experiment involving the manipulation of morph ratios in an experimental population and an investigation in a natural population with strong morph substructure both provided evidence that compatible pollen dilution limits fertility. Despite constraints on the functioning of distyly in N. peltata we found no evidence for evolutionary changes to the heterostylous syndrome, as reported in Nymphoides, including populations of N. peltata in other parts of its geographical range.
Maile C Neel - One of the best experts on this subject based on the ideXlab platform.
-
benefits of gene flow are mediated by individual variability in self compatibility in small isolated populations of an endemic plant species
Evolutionary Applications, 2017Co-Authors: Christopher T Frye, Maile C NeelAbstract:Many rare and endemic species experience increased rates of self-fertilization and mating among close relatives as a consequence of existing in small populations within isolated habitat patches. Variability in self-compatibility among individuals within populations may reflect adaptation to local demography and genetic architecture, inbreeding, or drift. We use experimental hand-pollinations under natural field conditions to assess the effects of gene flow in 21 populations of the central Appalachian endemic Trifolium virginicum that varied in population size and degree of isolation. We quantified the effects of distance from pollen source on pollination success and fruit set. Rates of self-compatibility varied dramatically among maternal plants, ranging from 0-100%. This variation was unrelated to population size or degree of isolation. Nearly continuous variation in the success of selfing and near-cross matings via hand-pollination suggest that T. virginicum expresses pseudo-self-fertility, whereby plants carrying the same S allele mate successfully by altering the self-incompatibility reaction. However, outcrossing among populations produced significantly higher fruit set than within populations, an indication of drift load. These results are consistent with strong selection acting to break down self-incompatibility in these small populations and/or early acting inbreeding depression expressed upon selfing. This article is protected by copyright. All rights reserved.
-
Benefits of gene flow are mediated by individual variability in self‐compatibility in small isolated populations of an endemic plant species
Evolutionary Applications, 2016Co-Authors: Christopher T Frye, Maile C NeelAbstract:Many rare and endemic species experience increased rates of self-fertilization and mating among close relatives as a consequence of existing in small populations within isolated habitat patches. Variability in self-compatibility among individuals within populations may reflect adaptation to local demography and genetic architecture, inbreeding, or drift. We use experimental hand-pollinations under natural field conditions to assess the effects of gene flow in 21 populations of the central Appalachian endemic Trifolium virginicum that varied in population size and degree of isolation. We quantified the effects of distance from pollen source on pollination success and fruit set. Rates of self-compatibility varied dramatically among maternal plants, ranging from 0-100%. This variation was unrelated to population size or degree of isolation. Nearly continuous variation in the success of selfing and near-cross matings via hand-pollination suggest that T. virginicum expresses pseudo-self-fertility, whereby plants carrying the same S allele mate successfully by altering the self-incompatibility reaction. However, outcrossing among populations produced significantly higher fruit set than within populations, an indication of drift load. These results are consistent with strong selection acting to break down self-incompatibility in these small populations and/or early acting inbreeding depression expressed upon selfing. This article is protected by copyright. All rights reserved.
Christopher T Frye - One of the best experts on this subject based on the ideXlab platform.
-
benefits of gene flow are mediated by individual variability in self compatibility in small isolated populations of an endemic plant species
Evolutionary Applications, 2017Co-Authors: Christopher T Frye, Maile C NeelAbstract:Many rare and endemic species experience increased rates of self-fertilization and mating among close relatives as a consequence of existing in small populations within isolated habitat patches. Variability in self-compatibility among individuals within populations may reflect adaptation to local demography and genetic architecture, inbreeding, or drift. We use experimental hand-pollinations under natural field conditions to assess the effects of gene flow in 21 populations of the central Appalachian endemic Trifolium virginicum that varied in population size and degree of isolation. We quantified the effects of distance from pollen source on pollination success and fruit set. Rates of self-compatibility varied dramatically among maternal plants, ranging from 0-100%. This variation was unrelated to population size or degree of isolation. Nearly continuous variation in the success of selfing and near-cross matings via hand-pollination suggest that T. virginicum expresses pseudo-self-fertility, whereby plants carrying the same S allele mate successfully by altering the self-incompatibility reaction. However, outcrossing among populations produced significantly higher fruit set than within populations, an indication of drift load. These results are consistent with strong selection acting to break down self-incompatibility in these small populations and/or early acting inbreeding depression expressed upon selfing. This article is protected by copyright. All rights reserved.
-
Benefits of gene flow are mediated by individual variability in self‐compatibility in small isolated populations of an endemic plant species
Evolutionary Applications, 2016Co-Authors: Christopher T Frye, Maile C NeelAbstract:Many rare and endemic species experience increased rates of self-fertilization and mating among close relatives as a consequence of existing in small populations within isolated habitat patches. Variability in self-compatibility among individuals within populations may reflect adaptation to local demography and genetic architecture, inbreeding, or drift. We use experimental hand-pollinations under natural field conditions to assess the effects of gene flow in 21 populations of the central Appalachian endemic Trifolium virginicum that varied in population size and degree of isolation. We quantified the effects of distance from pollen source on pollination success and fruit set. Rates of self-compatibility varied dramatically among maternal plants, ranging from 0-100%. This variation was unrelated to population size or degree of isolation. Nearly continuous variation in the success of selfing and near-cross matings via hand-pollination suggest that T. virginicum expresses pseudo-self-fertility, whereby plants carrying the same S allele mate successfully by altering the self-incompatibility reaction. However, outcrossing among populations produced significantly higher fruit set than within populations, an indication of drift load. These results are consistent with strong selection acting to break down self-incompatibility in these small populations and/or early acting inbreeding depression expressed upon selfing. This article is protected by copyright. All rights reserved.
