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postgraduate thesis: Mating systems in sympatric Hedyotis species (Rubiaceae) in Hong Kong : the breakdown of distyly and its impact on hybridization and self-fertilization
Title | Mating systems in sympatric Hedyotis species (Rubiaceae) in Hong Kong : the breakdown of distyly and its impact on hybridization and self-fertilization |
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Authors | |
Advisors | Advisor(s):Saunders, RMK |
Issue Date | 2020 |
Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
Citation | Mahadura, A. D.. (2020). Mating systems in sympatric Hedyotis species (Rubiaceae) in Hong Kong : the breakdown of distyly and its impact on hybridization and self-fertilization. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. |
Abstract | Many species in Hedyotis and related genera (Rubiaceae tribe Spermacoceae) exhibit
heterostyly, a floral polymorphism in which the anthers and stigmas occupy reciprocal
positions in two different ‘morphs’ within populations. This polymorphism is typically
associated with a biochemically mediated self-incompatibility system that prevents autogamy
and intra-morph fertilization. This study focuses on the reproductive biology, pollination
ecology and population genetics of the Hedyotis acutangula-shiuyingiae complex in Hong
Kong (comprising the often sympatric species H. acutangula, H. vachellii, H. shiuyingiae, H.
bodinieri and H. loganioides). Interspecific hybridization is investigated as a possible
explanation for the gene tree incongruence identified previously, with the breakdown of self-
and interspecific incompatibility hypothesized to have enabled hybridization within the
species complex. Correlations observed in self- and interspecific mate recognition systems
may be associated with unilateral incompatibility that acts as a barrier to hybridization: the
breakdown of specific self- and interspecific pollen recognition system might allow successful
interspecific mating. Hedyotis acutangula is demonstrated to be self- and interspecific
compatible, whereas H. vachellii, H. bodinieri and H. loganioides are self-compatible and
interspecific incompatible; H. shiuyingiae, in contrast, is strictly self-incompatible and
interspecific incompatible. The rapid growth of pollen tubes from heterospecific pollen in H.
acutangula indicates their ability to compete with conspecific pollen and undergo
interspecific hybridization. Population genetics data based on microsatellite markers provide
compelling evidence of the hybrid origin of H. bodinieri and H. loganioides and their
conspecificity. Reproductive biology and population genetic results confirmed the maternal
(H. acutangula) and paternal (H. shiuyingiae) parentage of these hybrids. Apis cerena, the
Asian honey bee, was identified as a pollinator, common to all the Hedyotis species studied.
The simultaneous flowering, overlapping anthesis and reproductive activity, shared
pollinators and interspecific pollen flow among sympatric Hedyotis species provide
compelling evidence for interspecific hybridization in the complex. Selection to avoid
interspecific hybridization can increase self-pollination in sympatric populations. The
functional breakdown of distyly and the presence of selfing syndromes in the sympatric
Hedyotis species studied suggests that self-pollination is favored, with anther dehiscence and
stigmatic receptivity prior to anthesis, self-compatibility and thrum morph-specific
spontaneous self-pollination in H. acutangula; self-incompatibility and relaxed stylar
dimorphism in H. vachellii; and stigmatic receptivity and anther dehiscence prior to anthesis
and high rates of spontaneous selfing in H. bodinieri. The success of self-pollination prior to
anthesis in H. bodinieri represents the first reported case of the co-occurrence of distyly and
pre-anthesis cleistogamy in Hedyotis. The functional breakdown of heterostyly and the
emergence of pre-anthesis cleistogamy represents an initial step in the evolutionary
transition from xenogamy to autogamy. The ability of cleistogamous pollen to compete with
inter-morph pollen provides the potential for pre-anthesis cleistogamy in H. bodinieri to break
the stability of distyly by reducing opportunities for outcrossing. Pre-anthesis cleistogamy is
likely a derived mechanism that ensures reproductive assurance despite potential mate and
pollinator limitation in the fragmented habitats in Hong Kong. |
Degree | Master of Philosophy |
Subject | Hedyotis - Reproduction - China - Hong Kong |
Dept/Program | Biological Sciences |
Persistent Identifier | http://hdl.handle.net/10722/297505 |
DC Field | Value | Language |
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dc.contributor.advisor | Saunders, RMK | - |
dc.contributor.author | Mahadura, Ashini Dias | - |
dc.date.accessioned | 2021-03-21T11:37:59Z | - |
dc.date.available | 2021-03-21T11:37:59Z | - |
dc.date.issued | 2020 | - |
dc.identifier.citation | Mahadura, A. D.. (2020). Mating systems in sympatric Hedyotis species (Rubiaceae) in Hong Kong : the breakdown of distyly and its impact on hybridization and self-fertilization. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. | - |
dc.identifier.uri | http://hdl.handle.net/10722/297505 | - |
dc.description.abstract | Many species in Hedyotis and related genera (Rubiaceae tribe Spermacoceae) exhibit heterostyly, a floral polymorphism in which the anthers and stigmas occupy reciprocal positions in two different ‘morphs’ within populations. This polymorphism is typically associated with a biochemically mediated self-incompatibility system that prevents autogamy and intra-morph fertilization. This study focuses on the reproductive biology, pollination ecology and population genetics of the Hedyotis acutangula-shiuyingiae complex in Hong Kong (comprising the often sympatric species H. acutangula, H. vachellii, H. shiuyingiae, H. bodinieri and H. loganioides). Interspecific hybridization is investigated as a possible explanation for the gene tree incongruence identified previously, with the breakdown of self- and interspecific incompatibility hypothesized to have enabled hybridization within the species complex. Correlations observed in self- and interspecific mate recognition systems may be associated with unilateral incompatibility that acts as a barrier to hybridization: the breakdown of specific self- and interspecific pollen recognition system might allow successful interspecific mating. Hedyotis acutangula is demonstrated to be self- and interspecific compatible, whereas H. vachellii, H. bodinieri and H. loganioides are self-compatible and interspecific incompatible; H. shiuyingiae, in contrast, is strictly self-incompatible and interspecific incompatible. The rapid growth of pollen tubes from heterospecific pollen in H. acutangula indicates their ability to compete with conspecific pollen and undergo interspecific hybridization. Population genetics data based on microsatellite markers provide compelling evidence of the hybrid origin of H. bodinieri and H. loganioides and their conspecificity. Reproductive biology and population genetic results confirmed the maternal (H. acutangula) and paternal (H. shiuyingiae) parentage of these hybrids. Apis cerena, the Asian honey bee, was identified as a pollinator, common to all the Hedyotis species studied. The simultaneous flowering, overlapping anthesis and reproductive activity, shared pollinators and interspecific pollen flow among sympatric Hedyotis species provide compelling evidence for interspecific hybridization in the complex. Selection to avoid interspecific hybridization can increase self-pollination in sympatric populations. The functional breakdown of distyly and the presence of selfing syndromes in the sympatric Hedyotis species studied suggests that self-pollination is favored, with anther dehiscence and stigmatic receptivity prior to anthesis, self-compatibility and thrum morph-specific spontaneous self-pollination in H. acutangula; self-incompatibility and relaxed stylar dimorphism in H. vachellii; and stigmatic receptivity and anther dehiscence prior to anthesis and high rates of spontaneous selfing in H. bodinieri. The success of self-pollination prior to anthesis in H. bodinieri represents the first reported case of the co-occurrence of distyly and pre-anthesis cleistogamy in Hedyotis. The functional breakdown of heterostyly and the emergence of pre-anthesis cleistogamy represents an initial step in the evolutionary transition from xenogamy to autogamy. The ability of cleistogamous pollen to compete with inter-morph pollen provides the potential for pre-anthesis cleistogamy in H. bodinieri to break the stability of distyly by reducing opportunities for outcrossing. Pre-anthesis cleistogamy is likely a derived mechanism that ensures reproductive assurance despite potential mate and pollinator limitation in the fragmented habitats in Hong Kong. | - |
dc.language | eng | - |
dc.publisher | The University of Hong Kong (Pokfulam, Hong Kong) | - |
dc.relation.ispartof | HKU Theses Online (HKUTO) | - |
dc.rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works. | - |
dc.rights | This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. | - |
dc.subject.lcsh | Hedyotis - Reproduction - China - Hong Kong | - |
dc.title | Mating systems in sympatric Hedyotis species (Rubiaceae) in Hong Kong : the breakdown of distyly and its impact on hybridization and self-fertilization | - |
dc.type | PG_Thesis | - |
dc.description.thesisname | Master of Philosophy | - |
dc.description.thesislevel | Master | - |
dc.description.thesisdiscipline | Biological Sciences | - |
dc.description.nature | published_or_final_version | - |
dc.date.hkucongregation | 2020 | - |
dc.identifier.mmsid | 991044351386403414 | - |