Pollination biology of a night‐flowering Galápagos endemic,Ipomoea habeliana (Convolvulaceae)

Ipomoea habeliana is an endemic, night‐flowering member of the Galápagos flora. Pollination experiments, flower‐visitor observations, nectar sampling, pollen transfer, and pollen to ovule ratio and pollen size studies were included in this project. The large, white flowers of this species set fruit via open pollination (55%), autonomous autogamy (51%), facilitated autogamy (91%), cross‐pollination (80%), diurnal open pollination (60%) and nocturnal open pollination (60%). Fruit set is pollen‐limited. Ants, beetles, crickets and hawk moths regularly visit the flowers. Ants are the most frequent visitors, but hawk moths are the only effective pollinators. Nectar is available throughout the night, but is most abundant early in the evening when hawk moth visits are most frequent. Experiments with fluorescent dust demonstrate intra‐ and inter‐plant pollen movement by hawk moths. Although this species is adapted for hawk moth pollination, it readily sets fruit via autonomous autogamy when no visits are made. Thus, it is concluded that it is facultatively xenogamous. Additional support for this conclusion is provided by the pollen to ovule ratio of 1407 and by the fact that the plants grow in a region that has few or no faithful pollinators. Conservation efforts for I. habeliana should include hand pollinations, which could significantly increase seed set. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 11–20.     

Development of the floral shoot and pre‐anthesis cleistogamy in Hydrobryopsis sessilis (Podostemaceae)

The reproductive biology of Hydrobryopsis sessilis (Podostemaceae, subfamily Podostemoideae), a reduced, threatened, aquatic angiosperm endemic to the Western Ghats of India, was examined. This is the first report on the transition from the vegetative to the reproductive phase in this plant, describing floral ontogeny, pollination and the breeding system. The cytohistological zonation of the apical meristem of the reproductive thallus is identical to that of the apical meristem of the vegetative thallus. The floral shoots do not replace vegetative shoots (i.e. the vegetative shoots never bear flowers), but form at new sites at the tip of the flattened plant body. Each floral shoot meristem is tiny, deep‐seated and concave and arises endogenously following lysigeny. The floral shoot meristem gives rise to four to six bracts in a distichous manner. The development of spathe, stamens and carpels is described. The ab initio dorsiventrality of the carpels and the occurrence of endothelium in the ovules are reported. The mature stigmas and anthers lie close to each other. The pollen germinates within undehisced anthers and the pollen tubes enter the stigmas in the unopened floral bud, leading to pre‐anthesis, complete, constitutional cleistogamy under water. The seed set is 63.2%. A significant finding is the penetration of several pollen tubes into the filaments of stamens in 16% of the flower buds, indicating a trend towards cryptic self‐fertilization. The Indian Podostemoideae appear to show a shift from xenogamy or geitonogamy or autogamy in a chasmogamous flower to complete autogamy in a cleistogamous flower. The floral modifications leading to cleistogamy in H. sessilis have been identified. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 222–236.     

Breeding system in the dichogamous hermaphrodite Silene acutifolia (Caryophyllaceae)

The breeding system of the dichogamous hermaphrodite species Silene acutifolia, endemic to north-west Spain and north and central Portugal, is examined. Pollen germinability and style-stigma receptivity were analysed to determine whether protandry is a barrier to self-fertilization. By 48 h after anthesis, pollen germinability had declined to approx. 10 %. The short straight styles are not receptive when flowers first open. They gradually elongate and curve outwards, develop stigma papillae and become receptive. There is no clear separation between stigma and style: the stigma papillae appear in a line along the length of the style. Fruit set is high regardless of pollen source; however, seed set is significantly reduced after both spontaneous and facilitated autogamy. Seed set following spontaneous autogamy was 30 % (86 % in controls) in 1998 and 33 % (87 % in controls) in 1999. Seed set following facilitated autogamy was 62 % (86 % in controls) in 1998 and 67 % (89 % in controls) in 1999. Thus, separation of the male and female phases does not prevent production of seeds by self-pollination, although it does reduce the likelihood of this. Furthermore, results of the present experiments indicate that this species has no self-incompatibility mechanisms (self-compatibility index = 0.98). The selfing rate in the study population was 0.41, which is supported by the lack of self-incompatibility systems and by the incomplete protandry.     

Floral biology and mechanisms of spontaneous self‐pollination in five neotropical species of Gentianaceae

Cross‐ and self‐fertilization in angiosperms are regulated by several factors, and a knowledge of the mechanism and time of spontaneous self‐pollination offers opportunities for a better understanding of the evolution of mating systems and floral traits. The floral biology of five species of Gentianaceae found in high‐altitude neotropical grassland is presented, with emphasis on the mechanisms that promote spontaneous self‐pollination. A presumed floral Batesian mimicry system is suggested between the rare and rewardless Zygostigma australe and Calydorea campestris, a species of Iridaceae with pollen‐flowers, pollinated by syrphids and bees. The floral morphology of the other four gentian species points to three different pollination syndromes: melittophily, phalaenophily and ornithophily. However, with the exception of the nocturnal Helia oblongifolia, flowers are nectarless and appear to exhibit non‐model deceptive mechanisms, providing similar floral cues to some sympatric rewarding species with the same syndrome. The similar mechanism of spontaneous self‐pollination in Calolisianthus pedunculatus, Calolisianthus pendulus and H. oblongifolia (Helieae) is based on the stigmatic movements towards the anthers. Selfing is promoted by movements of the style/stigma and of the corolla in Deianira nervosa and Z. australe (Chironieae), respectively. The movements of stamens, style and stigma during anthesis seem to be the most common method of spontaneous self‐pollination in angiosperms. It is suggested that the evolution of delayed spontaneous self‐pollination would be more expected in those taxa with dichogamous flowers associated with herkogamy. Such a characteristic is frequent in long‐lived flowers of certain groups of Asteridae, which comprise most documented cases of autonomous selfing. Thus, the presence of dichogamy associated with herkogamy (which supposedly evolved as a result of selection to promote both separation of male and female functions and the efficient transfer of cross pollen) may be the first step in the adaptive evolution of delayed selfing to provide reproductive assurance. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 357–368.     

Wind pollination in high-mountain populations of Hormathophylla spinosa (Cruciferae)

In this paper we study aspects of the breeding system of Hormathophylla spinosa (Crucifcrae) to identify the factors responsible for seed production in the absence of insect pollinators. The pollinator-exclusion experiments show that H. spinosa, under natural conditions, does not produce seed by apomixis or spontaneous autogamy. H. spinosa appears to be self-incompatible but slightly geitonogamous. Thus, this plant species needs pollen vectors for reproduction. The results of the wind-exclusion experiments performed during two different years in two populations of H. spinosa support the hypothesis that the wind acts as a pollen vector; flowers excluded from the wind had a lower fruit set and female fertility than flowers excluded from all pollinator insects (winged and wingless). This generalist pollination system (insects and wind) permits this species to colonize and sustain viable populations in high mountains, where this species is the only woody shrub living above 3000 m above sea level in the Sierra Nevada.     

Pollination of the heterostylous Galápagos native, <Emphasis Type="Italic">Cordia lutea</Emphasis> (Boraginaceae)

The hypothesis of this study was that in the Galápagos Islands, fruit and seed set via nocturnal pollination would exceed that of diurnal pollination due to greater insect activity at night typical of hot, arid regions. Cordia lutea, a heterostylous member of the Galápagos flora, was submitted to pollination experiments, visitor observations, nectar sampling, pollen transfer studies, pollen-ovule ratio studies, and pollen measurements. Flowers set fruit and seed via open pollination, autonomous autogamy, facilitated autogamy, facilitated cross-pollination, diurnal pollination, and nocturnal pollination. There was a significant difference in fruit set between flowers experiencing legitimate cross-pollinations (pin × thrum) and those experiencing all other pollination treatments except facilitated autogamy. There was no significant difference in seed set among any of the treatments, but there was a trend toward greater seed set for flowers experiencing open-pollination, legitimate cross-pollination, and nocturnal pollination. There was no significant difference in fruit set or seed set between flowers experiencing diurnal pollination and nocturnal pollination, although there was a trend toward greater seed set resulting from nocturnal pollination. Carpenter bees were the most effective diurnal pollinators, whereas moths were the most effective nocturnal pollinators. Of the two, moths are more efficient at transporting pollen from plant to plant. Results indicate that an overall low productivity of this species is due to pollen limitation exacerbated by nectar robbing. Cordia lutea exhibits a mixed mating system, producing a relatively low level of fruits through a combination of self- and cross-pollination, facilitated by the relatively few insects that are available.     

Size,structure and nitrogen content of seeds of Fabaceae in relation to nodulation

Looking for clues to explain the low rate and unpredictability of the pollination of allogamous, epiphytic orchids in the context of the success of the orchid family in general, we compared the pollination of two miniature twig epiphytes in Mexico: Notylia barkeri, a ‘weedy’, rewarding species, and Erycina crista‐galli, a rare, deceptive species. We measured the effects of the spatial organization of the flowers and various parameters of visibility and height above the ground in relation to the spatial organization of the seed capsules (which retrospectively measures the activity of the pollinators). The spatial presentation of the flowers of E. crista‐galli explained only 5% of the distribution of the seed capsules. For N. barkeri, with compound flowers, the spatial presentation, considering individual flowers or inflorescences, explained 12% and 45% of the distribution of the seed capsules, respectively, and all other interactions between the variables were insignificant. Both the deceptive and reward strategies resulted in the production of large numbers of seeds despite a low pollination percentage (1–5%). Notylia barkeri produced 11.8 (2005–6) and 53.7 (2007–8) times more seeds in total than E. crista‐galli. Furthermore, unlike E. crista‐galli, N. barkeri responded to loss of individuals after high winds with an increased production of flowers per plant. We suggest that orchids have evolved to specialize in chance, and instead of maximizing pollinator attraction, they maximize the seed production resulting from every casual encounter. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 165 , 251–266.     

Reproductive strategies of Strobilanthes kunthianus, an endemic, semelparous species in southern Western Ghats, India

Strobilanthes kunthianus (Acanthaceae) is a semelparous species with synchronized flowering and mast seeding once in 12 years. As semelparous plants have only one chance to reproduce, they are expected to develop effective strategies to prevent reproductive failure. The reproductive strategies of S. kunthianus were investigated by studying the floral traits, pollination biology, and breeding system that are critical for reproductive success. The species exhibits a series of floral traits: (1) gregarious flowering attracts a large number of Apis cerana indica , the major pollinator; (2) the stigma is sensitive to touch by the pollinator; in fresh flowers, the receptive surface faces the entry path of the incoming bee, facilitating pollen deposition; as an immediate response, the stigma curves backwards moving the receptive surface away from the path of the exiting bee, thus preventing autogamy and interference in pollen transfer; (3) flowers remain fresh for 2 days with receptive stigma and nectar and pollen reward. These traits render the species 100% pollination efficient to ensure a high seed set. As the species is self-compatible, the prevailing high degree of geitonogamous pollinations does not interfere with fruit set. The evolution of the adaptive floral traits has facilitated mast seeding in the species.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 155–163.     

Reproductive biology of a rare cactus, Opuntia spinosissima (Cactaceae), in the Florida Keys: why is seed set very low?

 Opuntia spinosissima (Martyn) Mill. (Cactaceae) is an extremely rare taxon with a single remaining wild population of 13 plants located on Little Torch Key, Florida. The plants rarely set viable seeds and most ovaries abscise without initiation of fruits. Pollination and breeding system were examined in Little Torch Key and in plant accessions located at Fairchild Tropical Garden. Four pollination treatments were carried out to test for apomixis, self-pollination, outcrossing, and autogamy; a control treatment was also monitored. Additionally, pollen viability, pollinators, and seed set and viability were investigated. On selfed, crossed, and open (control) stigmas pollen grains germinated, but the tubes usually did not reach the base of the style. This suggests that O. spinosissima has pre-zygotic self-incompatibility. None of the pairwise crosses set seed, so the extant plants were apparently not inter-compatible. Out of 173 manipulated and control flowers, only one set fruit. Although this flower was outcrossed, no pollen tubes germinated on the stigma; this suggests agamospermy, a process common in the Cactaceae. In those flowers where pollen tubes did reach the ovary they failed to penetrate ovules, suggesting ovarian inhibition or that this taxon has lost the ability to be fertilized. Most field-collected seeds were viable, but there is no seedling recruitment under natural conditions, and vegetative reproduction is common. Based on these findings, I hypothesize that O. spinosissima is a sterile polyploid and that the 13 extant plants are asexually derived from a single lineage. Received: 17 April 1998 / Revision accepted: 3 July 1998     

Reproductive system and fitness of Vriesea friburgensis,a self‐sterile bromeliad species

Reproductive biology and plant fertility are directly related to many aspects of plant evolution and conservation biology. Vriesea friburgensis is an epiphytic and terrestrial bromeliad endemic to the Brazilian Atlantic rainforest. Hand‐pollination experiments were used to examine the reproductive system in a wild population of V. friburgensis. Plant fertility was assigned considering flower production, fruit and seed set, seed germination, and pollen viability. Self‐sterility observed from spontaneous selfing and manual self‐pollination treatments may be the consequence of late‐acting self‐incompatibility. Hand‐pollination results indicated no pollen limitation in the population studied. Floral biology features such as a few daily open flowers, nectar production, and sugar concentration corroborate hummingbirds as effective pollinators, although bees were also documented as pollinators. Components of fitness such as high flower, fruit, and seed production together with high seed and pollen viability indicate that this wild population is viable. From a conservation point of view, we highlight that this self‐sterile species depends on pollinator services to maintain its population fitness and viability through cross‐pollination. Currently, pollinators are not limited in this population of V. friburgensis. Conversely, the maintenance and continuous conservation of this community is essential for preserving this plant–pollinator mutualism.     

Staminal hairs enhance fecundity in the pollen‐rewarding self‐incompatible lily Bulbine abyssinica

Flowering plants typically use floral rewards to attract animal pollinators. Unlike nectar, pollen rewards are usually visible and may thus function as a signal that influences landing decisions by pollen‐seeking insects. Here we artificially manipulate the presence of both pollen and staminal hairs (a putative false signal of pollen reward availability) in the hermaphroditic lily Bulbine abyssinica (Xanthorrhoeaceae) to investigate their effects on bee visitation and fecundity, and also test for trade‐offs between pollen production and seed production. Honeybees, the primary floral visitors, are probably not able to distinguish between colours of petals, staminal hairs and pollen of B. abyssinica, according to analysis of reflectance spectra in a bee vision model. Flowers with both pollen and hairs removed had the lowest levels of bee visitation, seed set and seed abortions. Flowers containing hairs had an ～50% increase in visitation rate and seed set compared with emasculated flowers, while intact controls had the highest seed abortion rate. Ovule discounting in intact flowers is probably due to ovarian self‐incompatibility (or strong early inbreeding depression) as ovules penetrated by tubes from self‐pollen uniformly failed to develop into seeds. These results show that staminal hairs can enhance plant fecundity by increasing attraction of pollen‐seeking insects to flowers without increasing the risk of ovule discounting through pollinator‐mediated self‐pollination. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 481–490.     

Pollination ecology of the pre-Pyrenean endemic Petrocoptis montsicciana (Caryophyllaceae): effects of population size

Petrocoptis montsicciana (Caryophyllaceae) is a threatened pre‐Pyrenean endemic that grows exclusively on caves and walls of limestone. We studied its pollination ecology by monitoring phenology and by evaluating pollen and nectar production, pollinator activity (frequency and behaviour of visitors), quantity and quality of pollination services, pollen/ovule ratio, and seed set in response to insect exclusion and self‐compatibility tests. We also analysed the effect of population size on reproductive mechanisms by comparing a large and a small population. Flowers of P. montsicciana produced nectar and were visited by Hymenoptera (79.7%), Diptera (11.5%), and Lepidoptera (8.8%). The most frequent pollinators (60.6% of total visits) were long‐tongued bees of the genus Anthophora. Both populations had a similar range of pollinators. We found a correlation between the number of visited flowers and the number of open flowers per census; 88.7% of pollen grains deposited on the stigmas were conspecific and the main competitor was another chasmophyte plant, Antirrhinum molle. Bagged flowers set seeds but significantly less so than hand‐self‐pollinated and control flowers. Thus, although self‐compatible and self‐pollinated, entomophilous pollination of P. montsicciana is required in order to explain c. 10–40% of total seed set, in accordance with P/O ratio estimations. Bagged flowers from the small population set significantly more seeds than the large one. Visitation rates were lower in the small population, but, unexpectedly, showed higher stigmatic pollen loads and similar or higher seed set. These results suggest an increase of spontaneous selfing rates in the small population, probably favoured by a smaller flower size, which can not only assure reproductive success when pollinators are scarce, but also provide additional potential to adapt to climatic changes. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 76 , 79–90.     

NONFRUITING HERMAPHRODITIC FLOWERS OF CALOCHORTUS LEICHTLINII (LILIACEAE): POTENTIAL REPRODUCTIVE FUNCTIONS

The breeding system, flowering display, and fruiting pattern of Calochortus leichtlinii Hook. (Liliaceae) was studied in the eastern Sierra Nevada. This species is capable of both autogamy and insect-mediated outcrossing. Either of these two means of pollination alone could affect full seed set; the populations studied were not pollination limited in 1983. Most individuals produced two flowers but set only one fruit. Flowers are not selectively matured on the basis of the quantity or purported quality of the pollen they receive; the first flower to open was matured in all experiments. Nonfruiting flowers have at least three potentially important reproductive functions: disseminating pollen, allowing plants to produce more seeds in response to an abundance of soil moisture, and setting seeds if the first flower fails to develop fruit.     

Effects of pollination and pollen source on the seed set ofPedicularis palustris

Habitat alteration can deteriorate plant-pollinator interactions and thereby increase the risk of population extinction. As part of a larger study on the effects of changes in land use on fen grassland vegetation, factors influencing the seed set of a short-lived, endangered wetland plant,Pedicularis palustris, were studied. We conducted field pollination experiments in one large and one small population. To investigate the effect of pollen source on seed set, individual flowers of caged plants were left unpollinated or were pollinated with pollen from the same flower, the same population or another population. To study pollen limitation and flower display, whole plants were subjected to pollinator exclosure, hand pollination or natural pollination. Self-compatibility was high, but differed between populations (61% and 97% of seed set after cross-pollination within populations). Cross-pollination between populations did not significantly alter seed number per capsule. Pollinator exclosure resulted in a very low seed set (<15% of natural seed set), despite high self-compatibility. The most likely explanations for high self-compatibility in combination with low autofertility are geitonogamy as reproductive assurance, selective neutrality of self-compatibility and phylogenetic constraints. Because of low autofertility, the seed set inP. palustris depends on pollinators. In the study populations, natural pollination was clearly sufficient for maximum seed production per plant, but seed set per capsule was significantly pollen-limited in the smaller population. Plants in this population also had a higher maximum percentage of simultaneously open flowers than those of the large population (31% vs. 13%), while flower longevity was generally extended without pollination. It is concluded thatP. palustris may influence pollinator behaviour and therefore the risk of pollen limitation by flower display.P. palustris showed a flexible reaction to differing pollination regimes without losses in overall seed set in the study populations.     

Pollination intensity and potential seed set in Passiflora vitifolia

Summary Initial seed set and fruit set were pollen-limited in a Costa Rican population of Passiflora vitifolia, a self-incompatible species with 200–350 ovules per flower. Pollination intensity was measured by counting the number of allogamous pollen grains on stigmas of the large one-day flowers. Hand-pollinations demonstrated that 25–50 pollen grains are required for fruit set, and >450 are needed for maximum seed set, with a pollen:seed ratio of about 1.6:1.0. Hummingbirds (Phaethornis superciliosus) delivered sufficient allogamous pollen for maximum seed set to only 28% of the flowers examined. Naturally pollinated flowers yielded fewer fruits and fewer seeds per fruit than those pollinated by hand. Most pollen transferred by humming-birds was self-incompatible; emasculated flowers yielded higher seed set than flowers with intact anthers. Visitation rates did not provide a good index of effective pollination.There were significant differences in ovule number, maximum seed set, and maximum per cent seed set among individual vines. More than half of an individual's flowers failed to set fruit, whether pollinated by birds or by hand. In this population, maximum reproductive potential may be limited by maternal resources for fruit development, but seed set varies with pollination intensity. Pollen-limited seed set may be a disadvantage of self-incompatibility, especially in species with many-seeded fruits.     

Does provenance matter? Fitness is not determined by genetic distance or the scale of pollen dispersal in Grevillea sphacelata (Proteaceae)

Understanding how the scale of pollen transfer determines the outcome of matings is important evolutionarily and a key issue in restoration ecology. We tested the effects of pollen transfer distance for the self‐incompatible shrub Grevillea sphacelata using (1) open pollination and transfer among (2) near neighbours, (3) neighbouring subpopulations and (4) populations separated by c. 4 km. We used AFLP markers to test for evidence of genetic differentiation within and among populations. Patterns of seed initiation suggest that open pollinated flowers were pollen limited, although in one subpopulation open seed set was greater than that achieved with pollen from near neighbours or other subpopulations. We detected no other effects of pollen source on seed initiation or seed and seedling development. In contrast, our genetic survey revealed significant spatial autocorrelation to 5 m, moderate differentiation of populations separated by up to 4 km and significant isolation by distance > 16 km. Our data suggest that, although dispersal of pollen may typically be localized, gene flow prevents localized adaptation or co‐adaptation and we detected no effects of inbreeding depression. In a restoration context, our results imply that movement of seed between populations separated by 4 km will not have detrimental consequences, despite significant differentiation at neutral genetic markers, and may be beneficial in maintaining genetic diversity and evolutionary potential. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 290–302.     

Resource limitation and pollen source (self and outcross) affecting seed production in two louseworts, Pedicularis siphonantha and P. longiflora (Orobanchaceae)

Two animal-pollinated hermaphrodite plants, Pedicularis siphonantha and P. longiflora , have been used to investigate factors limiting seed production in natural populations. To evaluate the potential seed abortion due to resources limitation, seed development has been observed and seed count conducted twice. Seed production per capsule has been compared when flowers have been removed and in a control group. Open pollination has been investigated and pollen supplementation undertaken to estimate the possibility of pollen limitation. Results show that seed abortion is frequent. Stigmatic pollen load is significantly higher than ovule number per ovary under open pollination for both species. Additional self and outcross pollen did not affect seed production. Flower removal significantly increases seed production per capsule, which indicates that seed production of the studied species is limited by available resources. To detect differences in seed production between flowers pollinated by self and outcross pollen, hand pollination of bagged flowers has also been conducted in natural populations of the two Pedicularis species. Compared with open pollination, hand-pollinating self-pollen decreases, while outcross pollen increases seed production per capsule. Such results suggest that inbreeding depression in the two self-compatible species may also result in partial seed abortion under open pollination if mixed pollen is deposited on the stigma. Our results also suggest that pollen interference plays an important role in low female fertility in the two Pedicularis species.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 83–89.     

Self‐incompatibility and post‐fertilization maternal regulation cause low fecundity in Aegle marmelos (Rutaceae)

Outbreeding confers an evolutionary advantage, and flowering plants have evolved a variety of contrivances for its maximization. However, neither fruit set nor seed set is realized to its fullest potential for a variety of reasons. The causes of low flower to fruit and seed to ovule ratios were investigated in naturally occurring bael trees (Aegle marmelos) at two sites for three seasons. The study established that the mass effect of synchronized flowering attracted a variety of insect pollinators to the generalist flowers; Apis dorsata was the most efficient pollinator. The seed to ovule ratio was low despite high natural pollination efficiency (c. 2400 pollen per stigma). Although pollination‐induced structural and histochemical changes in the style allowed many (9.5 ± 2.1) pollen tubes to grow, only cross‐pollen tubes could grow through the style. Gametophytic self‐incompatibility, manifested in the stylar zone, resulted in a significantly slower growth rate of self‐pollen tubes. The occurrence of obligate self‐incompatibility, coupled with increased self‐pollen deposition (geitonogamy), caused a significant number of flowers to abort. Fruit retention in the trees declined from 40% to 12% as a result of abortion of fruits at different stages of development. The number of mature fruits on a tree was negatively correlated (r = ?0.82) with their size. It is inferred that low natural fecundity in A. marmelos is primarily a result of obligate self‐incompatibility and strong post‐fertilization maternal regulation of allocation of resources to the developing fruits. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 572–585.     

Effects of herkogamy and inbreeding on the mating system of <Emphasis Type="Italic">Mimulus luteus</Emphasis> in the absence of pollinators

Self-pollination mechanisms are often invoked to explain plant reproduction in environments devoid of pollinators. However, populations may evolve a diverse variety of strategies depending on the ecological context of pollination. In this study we examined the pollination environment, inbreeding depression, and herkogamy of Mimulus luteus (Phrymaceae) in two consecutive years in an attempt to evaluate the extent to which these factors determine the current level of autogamy in this population. Results indicate that pollinators were almost absent in the study site in 2005 and 2006. Likewise, no evidence of significant inbreeding depression for seed production and seed germination was detected in the 2 years. Because M. luteus presents hermaphrodite flowers with ‘movement herkogamy’ (touch-sensitive stigmata that close upon contact), and anther–stigma separation, we evaluated the role of these traits in self-fertilization. First, we assessed the effects of pollen source (self- and xenogamous pollen, and control solution) on stigmata dynamics after pollen deposition, and seed production. We observed that stigmata that received pollen (self- and xenogamous hand-pollinated) remained closed for a longer time than flowers that received no pollen (control flowers). Seed production, however, was unaffected by pollen source, indicating that movement herkogamy does not prevent self-fertilization in this population. Second, a phenotypic selection analysis revealed that seed production increased with a reduction of anther–stigma separation in absence of pollinators (bagged flowers), suggesting that low herkogamy levels are promoted in this population. Our results indicate that lack of inbreeding depression, ineffective movement herkogamy, and selection against anther–stigma separation are factors that may contribute to the prevalence of autogamous reproductive mechanisms when M. luteus faces environments with scarce mating opportunity.     

Nocturnal and diurnal pollination of Clerodendrum molle (Verbenaceae) in the Gal��pagos Islands

The primary hypothesis of this study was that in the Galápagos Islands, fruit and seed set via nocturnal pollination would exceed that of diurnal pollination because of the greater insect activity at night typical of hot, arid regions. Clerodendrum molle, a widespread member of the Galápagos flora was submitted to pollination experiments, visitor observations, nectar sampling, pollen transfer studies, pollen?Covule ratio studies, and pollen measurements. Flowers set fruit and seed via open pollination, autonomous autogamy, facilitated autogamy, facilitated cross-pollination, diurnal pollination, and nocturnal pollination. Results indicate no significant difference in fruit set. Cross-pollinated flowers showed a significant increase in seed set over all treatments except facilitated autogamy. Nocturnal and diurnal fruit and seed set did not differ significantly. Nocturnal visitors included ants, spiders, hawk moths, and roaches whereas diurnal visitors included carpenter bees and ants. Galápagos members of C. molle exhibit incomplete protandry and set fruit via autonomous autogamy as a result of natural selection in an environment with few faithful pollinators. Overall low fruit and seed set are likely because of a combination of pollen and resource limitation, the latter exacerbated by nectar robbing. Studies of island angiosperms are crucial for complete understanding of the population dynamics of indigenous plants, which can assist conservation officials in protecting these species.