雌先熟植物茄参（茄科）的繁育系统

对分布于云南西北部的茄参（Mandragoraca caulescens）的繁育系统进行了研究。茄参的花期为5月底到6月初,单花持续时间为（9．9±2．8）d,其性表达方式为雌性先熟。有三种昆虫拜访茄参的花,白背熊蜂蜂王是最有效的传粉昆虫,但其访花频率很低;苍蝇和蚂蚁的访花频率较高,但苍蝇传粉效率十分有限;蚂蚁是窃蜜者。授粉实验证明茄参具有部分自交亲和能力,但由于雌性先熟,不具备主动自交能力。人工添加异交花粉显著提高了结实率和结籽数,证明茄参存在花粉限制。茄科的大部分植物是严格自交不亲和的,但茄参族的茄参是自交部分亲和,这和茄科天仙子族的部分成员类似。我们认为这两个独立起源于新世界向欧亚大陆扩散事件的族,各自从自交不亲和向自交亲和转变可能与高山地区恶劣的自然条件有关,这种繁育系统的进化模式是否具有普遍性值得进一步研究。     

雌先熟植物茄参 （茄科）的繁育系统

对分布于云南西北部的茄参（Mandragora caulescens）的繁育系统进行了研究。茄参的花期为5月底到6月初,单花持续时间为（9.9±2.8）d,其性表达方式为雌性先熟。有三种昆虫拜访茄参的花,白背熊蜂蜂王是最有效的传粉昆虫,但其访花频率很低;苍蝇和蚂蚁的访花频率较高,但苍蝇传粉效率十分有限;蚂蚁是窃蜜者。授粉实验证明茄参具有部分自交亲和能力,但由于雌性先熟,不具备主动自交能力。人工添加异交花粉显著提高了结实率和结籽数,证明茄参存在花粉限制。茄科的大部分植物是严格自交不亲和的,但茄参族的茄参是自交部分亲和,这和茄科天仙子族的部分成员类似。我们认为这两个独立起源于新世界向欧亚大陆扩散事件的族,各自从自交不亲和向自交亲和转变可能与高山地区恶劣的自然条件有关,这种繁育系统的进化模式是否具有普遍性值得进一步研究。     

Plant sexual systems, dichogamy, and herkogamy in the Venezuelan Central Plain

Sexual system, temporal variation in sex expression, and herkogamy were evaluated in 210 plant species in the Venezuelan Central Plain (VCP). This analysis was conducted considering the life forms, habitats, flowering time, pollination systems, and dispersal syndromes of the plant species. Hermaphrodite species dominated the community (75.2%; N=158), followed by monoecious taxa (17.1%; N=36), and then dioecious (7.6; N=16). Most species were adichogamous (=homogamous) (75.2%; N=155), followed by protandrous (16.5%; N=34), and protogynous (8.3%; N=17). The frequency of herkogamous species was higher (N=124; 60.2%) than the non-herkogamous (N=82; 39.8%). The three reproductive traits interacted significantly in a way that complements their effectiveness in promoting cross-pollination and avoidance of pollen–stigma interference: hermaphrodite-adichogamous species occurred in similar frequency to herkogamous and non-herkogamous species; monoecious-adichogamous species were mostly herkogamous, and all hermaphrodite, functionally dioecious-adichogamous, species were herkogamous. Sexual system, herkogamy, and dichogamy are associated with habitats in the savanna-forest mosaic of the VCP. The proportion of dioecious species decreased from trees to annual herbs and from forest to disturbed areas. Dichogamous species were most frequent for herbaceous plants, and non-herkogamous species dominated in annual herbs. The frequency of herkogamous species decreased from forest to disturbed areas. Sexual system was significantly associated with pollination system. Most dioecious and monoecious species had generalist pollination. A three-factor log linear analysis indicated that for any combination significantly. Sexual systems and herkogamy were associated with the respective seed dispersal syndrome. Most dioecious and herkogamous species were dispersed by frugivores, while monoecious plants tended to be dispersed by granivores and wind. Flowering time of dioecious species peaked during the dry–rainy transition period, whereas that of monoecious species was greatest during the rainy season. Therefore, specific biotic and abiotic conditions may enforce the occurrence of unisexuality in the community. In a similar way, dichogamous species tend to flower during the rainy season, associated with herbaceous life form and wind pollination. These results are discussed in the context of evolutionary and ecological trends.     

Comparative study of the sympatric ferns Culcita macrocarpa and Woodwardia radicans: Sexual phenotype

The sexual phenotypes of 1152 gametophytes from four populations of Culcita macrocarpa and Woodwardia radicans were monitored over a 1-year period. Gametophytes were maintained under three experimental conditions: (1) isolated, (2) pairs from the same sporophyte, or (3) pairs from different sporophytes. The frequencies of the sexual phenotypes did not vary significantly among these three conditions, and although there were some quantitative differences between populations, the sexual-phenotype sequences observed were species-specific. Gametophytes of C. macrocarpa were first male and then hermaphrodite: this sequence, together with the absence of antheridiogens, favours intragametophytic selfing. Natural populations of C. macrocarpa are presumably androdioecious. Gametophytes of W. radicans were first female and then hermaphrodite: this sequence and antheridiogen activity favour intergametophytic and even xenogamous mating. Despite these laboratory findings, populations of W. radicans are probably trioecious (because of the effects of antheridiogen). Few sporophytes of W. radicans were obtained in the present study, and none of C. macrocarpa: this is attributable to limiting illumination or substrate.     

Temporal mechanisms influencing gender expression and pollen flow within a self-incompatible perennial,Amianthium muscaetoxicum (Liliaceae)

Summary Temporal mechanisms that influence the synchrony of gender expression and the patterns of withinplant pollen flow were examined in Amianthium muscatoxicum. In this species self-incompatible pollinations can clog stigmas, interfere with the growth of outcrossed pollen tubes, and reduce fecundity. The majority of flowers have partial dichogamy: a two-day period of pollen dehiscence and a four-day period of pollen viability are nested in a six-day period of pistil viability. An indeterminate flowering sequence among flowers on the same plant and partial dichogamy within flowers help reduce pollen flow within the whole plant. The combined effects at both of these levels should reduce pollen wastage and lower the incidence of stigma clogging by incompatible self pollen.     

Is the dichogamy ofSalvia verbenaca (Lamiaceae) an effective barrier to self-fertilization?

Though dichogamy is generally interpreted as a means of preventing self-fertilization, the efficiency of this mechanism has been questioned. Little attention has been paid to functional aspects of male/female timing, such as variation over time in pollen germinability and in stigma receptivity. In the present study these aspects of male/female timing were investigated in the protandrous speciesSalvia verbenaca. To evaluate the effects of selfing, fruit set, total seed weight produced and seed/ovule ratio were also determined, (a) following artificial crossing, (b) following selfing (i.e. bagging) and (c) under natural conditions. Both pollen germinability and stigma receptivity peaked on the last day (day 3) of the flower's life, which presumably favours selfing. Neither fruit set nor seed/ovule ratio were significantly affected by pollination regime, but the total seed weight produced by artificially crossed plants was significantly higher than that produced by bagged or untreated plants. Neither fruit set, seed/ovule ratio nor total seed weight differed significantly between the two years of study. Thus, if aS. verbenaca flower receives outcrossing pollen it will produce a greater weight of seeds (with consequent advantages in terms of female reproductive success). However, the peaking of both pollen germinability and stigma receptivity on day 3 of the flower's life means that selfing is likely to occur if outcrossing pollen has not been received over the early part of the flower's life.     

Reproductive biology in a tropical shrubland of Venezuelan Guayana

Plant sexual systems were evaluated in a tropical shrubland community of Venezuelan Guayana. Of 89 plant species, 73.0% were hermaphrodite, 12.4% monoecious, 10.1 % submonoecious, and 4.5 % dioecious. Temporal variation of sexual expression showed that hermaphrodite species were mostly adichogamous and monoecious, submonoecious species dichogamous (protandrous andprotogynous). Herkogamy was an important mechanism promoting cross-pollination. Of 38 hermaphrodite species, 39.5 % were herkogamous. Plant sexual systems were not associated with life form. Most species were pollinated mostly by large and medium-size bees. Pollinator specificity and pollen load transportation, were higher for monoecious species than for hermaphrodite, submonoecious and dioecious ones. Both pollinator specificity and pollen transportation were not significantly different among representatives of the latter three sexual systems. Plant sexual systems were significantly associated with dispersal syndromes; dioecious species had bird-dispersal syndromes, the other sexual systems mostly anemochory, epizoochory and endozoochory; but many hermaphrodites were anemochorous.     

Up and down: stamen movements in Ruta graveolens (Rutaceae) enhance both outcrossing and delayed selfing

Background and Aims

Stamen movements directly determine pollen fates and mating patterns by altering positions of female and male organs. However, the implications of such movements in terms of pollination are not well understood. Recently, complex patterns of stamen movements have been identified in Loasaceae, Parnassiaceae, Rutaceae and Tropaeolaceae. In this study the stamen movements in Ruta graveolens (Rutaceae) and their impact on pollination are determined.

Methods

Pollination effects of stamen movements were studied in Ruta graveolens, in which one-by-one uplifting and falling back is followed by simultaneous movement of all stamens in some flowers. Using 30 flowers, one stamen was manipulated either to be immobilized or to be allowed to move freely towards the centre of the flower but be prevented from falling back. Pollen loads on stigmas and ovule fertilization in flowers with or without simultaneous stamen movement were determined.

Results

Pollen removal decreased dramatically (P < 0·001) when the stamen was stopped from uplifting because its anther was seldom contacted by pollinators. When a stamen stayed at the flower''s centre, pollen removal of the next freely moved anther decreased significantly (P < 0·005) because of fewer touches by pollinators and quick leaving of pollinators that were discouraged by the empty anther. Simultaneous stamen movement occurred only in flowers with low pollen load on the stigma and the remaining pollen in anthers dropped onto stigma surfaces after stamens moved to the flower''s centre.

Conclusions

In R. graveolens pollen removal is promoted through one-by-one movement of the stamen, which presents pollen in doses to pollinators by successive uplifting of the stamen and avoids interference of two consecutively dehisced anthers by falling back of the former stamen before the next one moves into the flower''s centre. Simultaneous stamen movement at the end of anthesis probably reflects an adaptation for late-acting self-pollination.     

Pollen-stigma interference in two gynodioecious species of Lamiaceae with intermediate individuals

BACKGROUND AND AIMS: Intermediate individuals (perfect flowers with very high degree of pollen abortion) in a gynodioecious plant species are very rare. A study is made of male-female relationships in each flower type and how floral characters can enhance the avoidance of 'pollen discounting' and 'self-pollination' in two gynodioecious species, Teucrium capitatum and Origanum syriacum. METHODS: The relationship between stigma receptivity and pollen viability was studied in two gynodioecious protandrous species of Lamiaceae, in addition to measuring some floral morphological characters over the life span of the flowers. KEY RESULTS: Three plant types in each species were found: plants bearing hermaphrodite (or male fertile) flowers (MF), female (or male sterile) flowers (MS) and intermediate flowers (INT). Plant types differed in flower size, with MS types being shorter than the other two types. There was no difference in style length among plant types in T. capitatum. Stigma receptivity decayed with floral age and was negative and significantly correlated with pollen viability in the two species, and positive and significantly correlated with style length in O. syriacum but only in MS flowers of T. capitatum. CONCLUSIONS: Reduction in size of floral characters is associated with male sterility, except style length in T. capitatum. MF flowers have two successive reproductive impediments: self-pollination and pollen-stigma interference. In both species, self-pollination is avoided by dichogamy (negative correlation between stigma receptivity and pollen viability), and pollen-stigma interference shows two different patterns: (1) style elongation in O. syriacum is characterized by a significant length increase, final MF dimensions are greater than those of MS dimensions, and style length is positively and significantly correlated with stigma receptivity; and (2) style movement in T. capitatum is characterized by a non-significant increase in style length, final MF floral dimensions are similar to those of MS dimensions, and there is no correlation between style length and stigma receptivity.