Pollination and late-acting self-incompatibility in Cyrtanthus breviflorus (Amaryllidaceae): implications for seed production

Background and Aims

Animal pollination is typically an uncertain process that interacts with self-incompatibility status to determine reproductive success. Seed set is often pollen-limited, but species with late-acting self-incompatibility (SI) may be particularly vulnerable, if self-pollen deposition results in ovule discounting. Pollination is examined and the occurrence of late-acting SI and ovule discounting assessed in Cyrtanthus breviflorus.

Methods

The pollination system was characterized by observing floral visitors and assessing nectar production and spectral reflectance of flowers. To assess late-acting SI and ovule discounting, growth of self- and cross-pollen tubes, and seed set following open pollination or hand pollination with varying proportions of self- and cross-pollen, were examined.

Key Results

Native honeybees Apis mellifera scutellata pollinated flowers as they actively collected pollen. Most flowers (≥70 %) did not contain nectar, while the rest produced minute volumes of dilute nectar. The flowers which are yellow to humans are visually conspicuous to bees with a strong contrast between UV-reflecting tepals and UV-absorbing anthers and pollen. Plants were self-incompatible, but self-rejection was late-acting and both self- and cross-pollen tubes penetrated ovules. Seed set of open-pollinated flowers was pollen-limited, despite pollen deposition exceeding ovule number by 6-fold. Open-pollinated seed set was similar to that of the cross + self-pollen treatment, but was less than that of the cross-pollen-only treatment.

Conclusions

Flowers of C. breviflorus are pollinated primarily by pollen-collecting bees and possess a late-acting SI system, previously unknown in this clade of the Amaryllidaceae. Pollinators of C. breviflorus deposit mixtures of cross- and self-pollen and, because SI is late-acting, self-pollen disables ovules, reducing female fertility. This study thus contributes to growing evidence that seed production in plants with late-acting SI systems is frequently limited by pollen quality, even when pollinators are abundant.     

The relation between oilseed rape and pollination of later flowering plants varies across plant species and landscape contexts

Increasing cultivation of oilseed rape may have consequences for pollinators and wild plant pollination. By providing pollinating insects with pollen and nectar, oilseed rape benefits short-tongued, generalist insect species. Long-tongued bumble bee species, specialized to other flower types, may instead be negatively affected by increased competition from the generalists (e.g. due to nectar-robbing of long-tubed flowers) after oilseed rape flowering has ceased. We expected that the increased abundance of short-tongued pollinators and reduced abundance of long-tongued bumble bees in landscapes with a high proportion of oilseed rape would impact the pollination of later flowering wild plant species. In addition, we expected contrasting effects on plants pollinated by short-tongued pollinators and those pollinated by long-tongued bumble bees. We predicted that semi-natural grasslands, which provide insects with alternative floral resources, would reduce both negative and positive effects on pollination by mitigating competition between pollinators.In 16 semi-natural grasslands, surrounded by agricultural landscapes, with a variation in both the proportion of oilseed rape and the proportion of semi-natural grassland within 1 km, we studied reproductive output in two species of potted plants with different pollination strategies: the woodland strawberry (Fragaria vesca) and red clover (Trifolium pratense). The first species is mainly pollinated by short-tongued pollinators, e.g. hoverflies and solitary bees, and the latter by long-tongued bumble bees. Both species flowered after oilseed rape.Strawberry weight was higher in landscapes with a high proportion of oilseed rape, but only in landscapes with a low proportion of semi-natural grassland. The proportion of developed achenes was also positively related to the proportion of oilseed rape, but only during the latest flowering period. In contrast, red clover seed set was unrelated to the proportion of oilseed rape. Whereas the discrepancy between the two strawberry measurements calls for further research, this study suggests that oilseed rape can affect later flowering plants and that the impact differs among species.     

Extremely reduced sexual reproduction in the clonal cactus Echinopsis thelegona

Sexual and asexual reproduction may occur simultaneously in some plant species. Under certain environmental conditions asexual reproduction is predominant, which generates ecological consequences on sexual fecundity. In this context, we studied the reproductive ecology of the creeping clonal cactus Echinopsis thelegona in La Bodega (Salta, Argentina), where low fruit and seed production was preliminarily observed. Specifically, we studied the flower availability, fruit and seed production, reproductive system, floral visitors and effects of neighbor ramets on reproductive success. The number of available flowers per day was low, and fruit production was low or null as well. Echinopsis thelegona is self-incompatible. Although its flowers have sphingophilous traits, we did not find evidence of moths visiting them. Only native and exotic bees visited the flowers of this species, though with a low number of visits. Therefore, nocturnal visitors were not registered as pollinators of E. thelegona, perhaps because of their low local abundances. On the other hand, bees behaved as inefficient pollinators of E. thelegona due to their foraging behavior, which moves pollen within individuals. A pollen-addition experiment revealed that there is no fruit production at short distances among ramets. Therefore, the combination of self-incompatibility, low flower production and low local abundance of pollinators could account for the low fruit production observed in this species. This finding suggests that populations of E. thelegona persist by clonality and that they tend toward the loss of sexuality.     

Domestication of cardamom (Elettaria cardamomum) in Western Ghats, India: divergence in productive traits and a shift in major pollinators

Background and Aims

Elettaria cardamomum, a highly priced spice, is native to the Western Ghats of South India. Wild populations still occur in isolated patches in their natural habitats; however, much of today''s commercial product comes from cultivated sources. There is no information on domestication-related traits of this species; the main objective of this study was to compare wild and cultivated populations of cardamom in terms of vegetative and reproductive features in order to identify domestication syndromes and to examine whether the two populations have developed reproductive barriers.

Methods

Two wild populations and five cultivated plantations were used for the present study. Vegetative and floral traits, flowering phenology, pollination biology and breeding systems of wild and cultivated populations were compared. Effective pollinators amongst floral visitors were identified by confirming pollen transfer as well as by fruit set following their visit to virgin flowers. Manual pollinations were carried out in order to study the breeding systems of the two populations and reproductive barriers, if any, between them.

Key Results

Several productive traits including the number of branches, number of inflorescences, and total number of flowers per clump, number of flowers that open each day, the duration of flowering, the length of the flower and the amount of nectar per flower are significantly greater in cultivated cardamom. The principal pollinators in wild cardamom are solitary bees, Megachile sp. and two species of Amegilla, whereas those in cultivated cardamom are the social bees Apis dorsata, A. cerana and Trigona iridipennis. Both the wild and cultivated populations are self-compatible and there are no reproductive barriers between the two populations.

Conclusions

Domestication in cardamom has brought about significant changes in vegetative and reproductive traits and a shift in effective pollinators from native solitary bees to social bees. The shift in pollinators seems to be due to the availability of a large number of flowers for prolonged periods in cultivated cardamom that can attract and sustain social bees, rather than due to co-evolution of the flower and the pollinator.Key words: Elettaria cardamomum, wild cardamom, domestication, Amegilla sp., Apis cerana, Apis dorsata, Megachile sp., pollination efficiency, solitary bees, social bees     

Divergence on floral traits and vertebrate pollinators of two endemic Encholirium bromeliads

Shifts in pollen vectors favour diversification of floral traits, and differences in pollination strategies between congeneric sympatric species can contribute to reproductive isolation. Divergence in flowering phenology and selfing could also reduce interspecific crossing between self‐compatible species. We investigated floral traits and visitation rates of pollinators of two sympatric Encholirium species on rocky outcrops to evaluate whether prior knowledge of floral characters could indicate actual pollinators. Data on flowering phenology, visitation rates and breeding system were used to evaluate reproductive isolation. Flowering phenology overlapped between species, but there were differences in floral characters, nectar volume and concentration. Several hummingbird species visited flowers of both Encholirium spp., but the endemic bat Lonchophylla bokermanni and an unidentified sphingid only visited E. vogelii. Pollination treatments demonstrated that E. heloisae and E. vogelii were partially self‐compatible, with weak pollen limitation to seed set. Herbivores feeding on inflorescences decreased reproductive output of both species, but for E. vogelii the damage was higher. Our results indicate that actual pollinators can be known beforehand through floral traits, in agreement with pollination syndromes stating that a set of floral traits can be associated with the attraction of specific groups of pollinators. Divergence on floral traits and pollinator assemblage indicate that shifts in pollination strategies contribute to reproductive isolation between these Encholirium species, not divergence on flowering phenology or selfing. We suggest that hummingbird pollination might be the ancestral condition in Encholirium and that evolution of bat pollination made a substantial contribution to the diversification of this clade.     

Pollination and reproductive biology of twelve species of neotropical Malpighiaceae: stigma morphology and its implications for the breeding system

BACKGROUND AND AIMS: This study on reproductive biology examines the stigmatic morphology of 12 Brazilian Malpighiaceae species with regard to their pollination and breeding system. METHODS: The species were studied in natural populations of a semi-deciduous forest fragment. Style tips were processed for observation by SEM and pollen-tube growth was analyzed under fluorescence microscopy. The breeding system was investigated by isolating flowers within waterproof bags. Floral visitors were recorded through notes and photographs. KEY RESULTS: Flowers are yellow, pink or white, protogynous, herkogamous and sometimes lack oil glands. While Banisteriopsis pubipetala has functional female flowers (with indehiscent anthers), 11 species present hermaphrodite flowers. Stigmas of these species may be terminal, with a slightly concave surface, or internal, consisting of a circular cavity with a large orifice, and are covered with a thin, impermeable cuticle that prevents pollen from adhering, hydrating, or germinating. Malpighiaceae have a special type of 'wet' stigma, where a secretion accumulates under the cuticle and is released by mechanical means-mainly rupture by pollinators. Even though six species show a certain degree of self-compatibility, four of them present a form of late-acting self-incompatibility, and the individual of B. pubipetala is agamospermous. Species of Centris, Epicharis and Monoeca bees pollinate these flowers, mainly collecting oil. Some Epicharis and Monoeca species collected pollen by vibration. Paratetrapedia and Tetrapedia bees are pollen and oil thieves. CONCLUSIONS: The Malpiguiaceae species studied are pollinator-dependent, as spontaneous self-pollination is limited by herkogamy, protogyny and the stigmatic cuticle. Both the oil- and pollen-collecting behaviours of the pollinators favour the rupture of the stigmatic cuticle and the deposition of pollen on or inside the stigmas. As fruit-set rates in natural conditions are low, population fragmentation may have limited the sexual reproduction of these species.     

Transitions between self-compatibility and self-incompatibility and the evolution of reproductive isolation in the large and diverse tropical genus Dendrobium (Orchidaceae)

Background and Aims The evolution of interspecific reproductive barriers is crucial to understanding species evolution. This study examines the contribution of transitions between self-compatibility (SC) and self-incompatibility (SI) and genetic divergence in the evolution of reproductive barriers in Dendrobium, one of the largest orchid genera. Specifically, it investigates the evolution of pre- and postzygotic isolation and the effects of transitions between compatibility states on interspecific reproductive isolation within the genus.Methods The role of SC and SI changes in reproductive compatibility among species was examined using fruit set and seed viability data available in the literature from 86 species and ∼2500 hand pollinations. The evolution of SC and SI in Dendrobium species was investigated within a phylogenetic framework using internal transcribed spacer sequences available in GenBank.Key Results Based on data from crossing experiments, estimations of genetic distance and the results of a literature survey, it was found that changes in SC and SI significantly influenced the compatibility between species in interspecific crosses. The number of fruits produced was significantly higher in crosses in which self-incompatible species acted as pollen donor for self-compatible species, following the SI × SC rule. Maximum likelihood and Bayesian tests did not reject transitions from SI to SC and from SC to SI across the Dendrobium phylogeny. In addition, postzygotic isolation (embryo mortality) was found to evolve gradually with genetic divergence, in agreement with previous results observed for other plant species, including orchids.Conclusions Transitions between SC and SI and the gradual accumulation of genetic incompatibilities affecting postzygotic isolation are important mechanisms preventing gene flow among Dendrobium species, and may constitute important evolutionary processes contributing to the high levels of species diversity in this tropical orchid group.     

Adding Perches for Cross-Pollination Ensures the Reproduction of a Self-Incompatible Orchid

Background

Outcrossing is known to carry genetic advantages in comparison with inbreeding. In many cases, flowering plants develop a self-incompatibility mechanism, along with a floral component adaptation mechanism, to avoid self-pollination and to promote outbreeding. Orchids commonly have a lip in their flower that functions as the a visiting plate for insect pollinators. Aside from the lip, however, many species (including Coelogyne rigida) have sheaths around the axis of inflorescence. The function of these sheaths remains unknown, and has long been a puzzle to researchers.

Methodology/Principal Findings

We investigated the function of these sheaths in relation to the lip and the pollinators, as well as their role in the modes of pollination and reproduction of Coelogyne rigida in 30 flowering populations of orchids in the limestone area of Southeast Yunnan, China. We found that self-incompatible C. rigida developed specialized bird perches around the basal axis of inflorescence to attract sunbirds and to complement their behavioral tendency to change foraging locations frequently. This self-incompatibility mechanism operates separately from the floral component adaptation mechanism. This mechanism thus prevents bees from repeatedly visiting the floral lip of the same plant which, in turn, results in autogamy. In this way, instead of preventing autogamy, C. rigida responds to these negative effects through a highly efficient cross-pollination method that successfully transfers pollen to different plants.

Conclusions

The proposed method ensures reproductive success, while offsetting the infertile self-pollination by insects, thereby reducing mating costs and addressing the lack of cross-pollination. The adaptation provides a novel and striking example of structural adaptation that promotes cross-pollination in angiosperms.     

Tibouchina pulchra (Melastomataceae): reproductive biology of a tree species at two sites of an elevational gradient in the Atlantic rainforest in Brazil

Low-temperature environments interfere with plant reproduction by reducing the frequency of pollinators, and this may favour reproductive strategies such as self-pollination and apomixis. Tibouchina pulchra is a common tree species that occurs at high and low sites of the Brazilian Atlantic rainforest. This study focussed on the pollination biology and breeding system of this species, describing the pollinators and the reproductive success at the two sites of an elevational gradient. Observations were made to determine extent of flowering and fruiting, to identify the richness and abundance of pollinators, and to record data on the floral and reproductive biology at these two sites. Despite more dense flowering at the high site, five visits of bees (two species) were recorded during the observation time (60?h), whereas at the low site there were 948 visits (seven species) during the same period. In contrast with the low site, the flowers of the high site released and received few pollen grains on the stigma. At the high site less fruit was set with fewer seeds as a result of open pollination than at the low site; at that site, however, more seeds were obtained from cross-pollination than at the low site. Tibouchina pulchra is self-compatible; however it is not apomictic and needs pollinators for seed set at both sites. Life-history traits other than the breeding system, for example more dense flowering, advantage of greater fertility in cross-pollination, and multiple reproductive events during the lifetime of the tree may reduce inbreeding depression, increase the hybrid vigour, and balance the lack of pollinators at the high site.     

Experimental sympatry suggests geographic isolation as an essential reproductive barrier between two sister species of Pedicularis

Although mechanical isolation mediated by shared pollinators has been considered as a classic model of pollinator-mediated floral isolation in Pedicularis, a superdiverse genus in Hengduan Mountains, southwest China, there has been no empirical study of interspecific pollen flow between closely related species. We examined reproductive barriers at six different stages between Pedicularis cranolopha and Pedicularis tricolor, two sister species. The two sister species were geographically isolated from each other based on our field survey and the records of herbarium specimens. Translocation experiments showed that flowering phenology partly overlapped and bumblebee pollinators did not discriminate between flowers of the two species. Bumblebee interspecific moves could mediate interspecific pollination as traced using fluorescent powder, in which pollen analogs placed on one species were transferred to the stigmas of the other species in experimental plots containing both species. Heterospecific pollen tubes grew in the style as well as conspecific pollen in hand-pollination experiments. Reciprocal hybridization between the two species could produce (partially) viable seeds, suggesting weak post-pollination barriers. Our results showed that geographic isolation was an important barrier of two species, and the total reproductive isolation between two species was incomplete when without geographical isolation. The formation of Big Snow Mountains could introduce an important pre-zygotic reproductive barrier between the two sister species of Pedicularis; such geographical isolation could be responsible for allopatric speciation, giving a clue to understanding the rapid radiation on mountain areas.     

Is the pollination biology of Bathysa and Schizocalyx consistent with their segregation? A first approach for two sympatric species in southeastern Brazil

Tribe Condamineeae appears to be well supported in recent phylogenetic studies. However, the species of Bathysa were divided into two clades, leading to restoration of Schizocalyx. We studied the reproductive biology of one species from each clade, which occur sympatrically in the montane Brazilian Atlantic forest. Flowering overlap was short (from December to March in B. australis and from February to June in S. cuspidatus). The flowers of both species are protogynous and homostylous and last for about 3 days. The unit of pollination in B. australis is the inflorescence. Its flowers have a greenish hypocrateriform corolla (tube about 5 mm long) and were mainly pollinated by bees and wasps in search of nectar. Schizocalyx cuspidatus has white flowers with an infundibuliform corolla (tube about 8 mm long), and its main pollinators were stingless bees in search of pollen. The pollination systems of the two species did not correspond to their pollination syndromes. Morphological differences between Bathysa and Schizocalyx were reflected in their pollination systems, with greater phenotypic specialization in S. cuspidatus, the flowers of which offer pollen as the main resource, an unusual feature within Rubiaceae. Schizocalyx cuspidatus showed higher reproductive capacity by having more inflorescences per plant, more ovules per flower, and twice the proportion of flowering individuals. However, the reproductive efficiency (fruit set, seed/ovule ratio) did not differ between the species, despite the higher frequency of visits by pollinators to S. cuspidatus. Self-compatibility in B. australis and self-incompatibility in S. cuspidatus seem to explain these results.     

Interaction between oil-collecting bees and seven species of Plantaginaceae

Oil-bee/oil-flower mutualism evolved through multiple gains and losses of the ability to produce floral oil in plants and to collect it in bees. Around 2000 plant species are known to produce floral oils that are collected by roughly 450 bee species, which use them for the construction of nests and for the larval food. The Plantaginaceae contain several Neotropical species that produce floral oils, the main reward offered by these plants. In the genera Angelonia, Basistemon, Monopera and Monttea, mainly associated with Centris bees, the floral oil is produced in trichomes that are located in the inner corolla. The pollinators of a few species in this neotropical clade of Plantaginaceae are known, and the role of flower morphology as well as the requirements from pollinators and the role of other groups of bees in the pollination of these flowers remains unclear. In this paper we provide a list of the flower visitors of seven Plantaginaceae species (six Angelonia species and Basistemon silvaticus) analyzing their behavior to highlight the legitimate pollinators and illustrating little known aspects of flower morphology and oil-collecting apparatuses of the bees. Two general morphological patterns were observed in the Angelonia flowers: deep corolla tube with short lobes, and short corolla tube with long lobes. Corolla tubes of different length result in pollen adherence to different parts of the insect body. The six Angelonia species and B. silvaticus flowers were visited by 25 oil-collecting bee species (10 Centris, 11 Tapinotaspidini and 4 Tetrapedia species), the majority acting as legitimate visitors. The flowers were also visited by illegitimate bee pollinators, which collected pollen but do not transfer it to the female organ. Specialized collectors of Plantaginaceae floral oils present modifications on the first pair of legs, mainly in the basitarsi but also extended to the tarsomeres. The new records of Tapinotaspidini and Centridini species acting as specialized pollinators of Plantaginaceae suggest that there is a geographic variation in the pollinators of the same plant species, and that the evolutionary scenario of the historical relationships between oil-collecting bees and floral oil producing plants is more complex than previously considered.     

Phenology,pollination, and breeding system of the threatened tree Caesalpinia echinata Lam. (Fabaceae), and a review of studies on the reproductive biology in the genus

Caesalpinia echinata (brazilwood) is a threatened tree endemic to the Brazilian Atlantic forest with a global importance as it is worldwide used to manufacture the most desirable bows for violins, violas, and cellos. Although there is an international initiative for its conservation, there is a lack of studies on the reproductive biology of the species, as for the genus, a fundamental understanding for the conservation of any species. In this paper, we investigated the phenology, pollination, and breeding system of C. echinata, presenting some conservation guidelines for the species, together with a review of studies on the reproductive biology in Caesalpinia s.l. The genus has a complex taxonomic history with recent attempts to reassign its limits. Pending a final resolution of the placing of some species (including C. echinata) our revision covers the traditional Caesalpinia s.l. and includes annotations indicating to which segregate genus each species is now considered to belong, as well as the appropriate combination where this has already been published. Field work was undertaken from October/2004 to December/2006 at the Tapacurá Ecological Station, northeastern Brazil. Flowering occurred mainly in the dry season and the peak of seed dispersal was at the beginning of the wet season. Anthesis is diurnal, lasting 1 day. The flowers are zygomorphic, yellow, sweet-scented, and the effective pollinators were mainly medium-sized to large bees of the genera Centris and Xylocopa, together with the introduced Apis mellifera. Nectar volume and sugar concentration averaged 2.9±1.0 μL and 29.5±9.4%, respectively. The ovary has 1–4 ovules (2.35±0.58) and the pollen/ovule ratio was 5631.2; pollen viability was high (95.9±4.8%). Natural fruit set was low (9.2%) with mature fruits averaging 1.7±0.9 seeds. Results of the controlled pollinations and analysis of pollen tube growth revealed C. echinata presents late-acting self-incompatibility. The pollination biology and breeding system of C. echinata are discussed, together with available data on its genetics and physiology, in terms of best conservation practice for this endangered species. Data on the reproductive biology of the genus are scarce, revealing the predominance of bee pollination and SI system, with the occurrence of late-acting self-incompatibility mechanisms in some species.     

Pollinators and crossability as reproductive isolation barriers in two sympatric oil-rewarding <Emphasis Type="Italic">Calceolaria</Emphasis> (Calceolariaceae) species

Pollinator species are widely accepted as an important factor in plant reproductive isolation. Although mostly investigated in plants visited by different groups of pollinators (e.g., hummingbirds vs bees), few studies have examined the role of pollinators belonging to the same taxonomic group (e.g., only bees) on plant reproductive isolation. In this study, we investigate this question by evaluating pre- and post-zygotic mechanisms putatively involved in the reproductive isolation of two oil-rewarding sympatric Calceolaria species (i.e., Calceolaria filicaulis and C. arachnoidea) in an Andean ecosystem of Chile. We estimated reproductive isolation values using a combination of field (pollinator visitation rates) and experimental (intra and interspecific manual cross-pollination and seed germination of parents and hybrids) evidence. The two Calceolaria species were preferentially visited by different oil-collecting bee species. Results from hand cross-pollination experiments indicate that intraspecific crossings produced significantly more seeds than interspecific ones. Notwithstanding, seed germination essays did not reveal differences between parental and hybrids. Taken together, these results suggest that pollinator species are responsible for most of the reproductive isolation in the two Calceolaria species studied here. This study is the first assessment of pollinator-mediated reproductive isolation in Calceolaria species and the first to document reproductive barriers in oil-rewarding plants.     

Self-interference is reduced in a secondary pollen presentation species, Duperrea pavettifolia (Rubiaceae)

Occurrence of secondary pollen presentation (SPP) is evidenced for Duperrea pavettifolia. For this, self-pollen was presented on the stigma and reduced fertilization was observed in this case. The receptive area located in the furrow of the stigma becomes receptive from the third day of elongation growth. Fruit set upon hand pollination with pollen from other individuals was significantly higher than the results of selfed, bagged, emasculated and control treatments. However there was no difference in pollen tube growth rate between selfed and crossed pollen on a receptive stigma. Hawkmoths and butterflies were effective pollinators for D. pavettifolia, but the visiting frequencies were very low. Stingless bees removed pollen from the unreceptive stigma which had no contribution to reproductive success. High level of outcrossing in D. pavettifolia was demonstrated by molecular analyses using the simple sequence repeats (SSR) method. Although the wild populations of D. pavettifolia are small and with fragmented distribution, the genetic diversity of seedlings was high, with fluctuations among years. Our results indicated that protandry and the visitation of stingless bees reduced the amount of self-pollen on the still unreceptive stigma and self-incompatibility prevented fertilization by un-removed self-pollen.     

Pollination ecology in sympatric winter flowering Helleborus (Ranunculaceae)

We studied biotic and abiotic factors that influence pollination in two sympatric winter flowering species. Helleborus foetidus and Helleborus bocconei flower simultaneously in winter. Although climatic conditions are not favorable for biotic pollination both species rely mainly on large bees of the genus Bombus. At the beginning of flowering, harsh climatic conditions are restrictive for insect visits. As flowering continues and temperatures rise, pollinator activity increases. The two plant species share pollinators that visit them indiscriminately. The flowers of the two species differ in form and insects visit H. foetidus by inserting their heads and H. bocconei ventrally: pollen load on insects is highly specialized. With the arrival of spring, many other species start to bloom and in spite of the large number of flowers still on the plants insects abandon Helleborus species. At the end of spring increasing biotic interactions take away pollinators from the Helleborus species.     

Reproductive ecology of Ameroglossum pernambucense (Scrophulariaceae): is this ornithophilous and threatened shrub highly adapted to a naturally fragmented habitat?

Many rare plants exist in a naturally fragmented distribution and are expected to exhibit reproductive adaptations to isolation. Thus, understanding the reproduction of these plants might be important in predicting the future of artificially fragmented species. Ameroglossum pernambucense is a threatened ornithophilous shrub with naturally fragmented populations on granite outcrops in north-eastern Brazil. The current research studied two populations of A. pernambucense and determined if three reproductive features (mating system, flowering phenology and nectar dynamics) facilitate the colonisation of new areas and the gene flow among the outcrops. To verify the species’ reproductive efficiency, pollinator efficiency and pollen limitation were tested. Ameroglossum pernambucense has a mixed mating system, and pollinators increased seed production. The pollinator efficiency test revealed that hummingbirds can supply the entire pollen demand. No pollen limitation was detected. Variation in sunset time was the main factor to explain the flowering pattern of A. pernambucense. Nectar was abundantly produced after successive removals. The reproductive traits observed in A. pernambucense were interpreted as highly adapted to its fragmented condition. Phenological photoperiodic regulation may increase the flowering synchrony and chances of gene flow among outcrops in environmentally distinct microsites. The mixed mating system favours both the colonisation of isolated outcrops and allogamy. High flower production and its high energetic value may have an important role in pollinator attraction and may increase long-distance outcrossing. Our data suggest that artificially fragmented plants with reproductive features similar to those observed here might be reproductively less susceptible to fragmentation.     

Melittophily and ornithochory in Tilesia baccata (L.f.) Pruski: An Asteraceae of the Atlantic Forest understory with fleshy fruits

Many Asteraceae species inhabit open vegetation areas and, as a rule, members of this family have dry, wind-dispersed fruits. Tilesia baccata, on the other hand, occurs in forested areas and, differently from all neotropical Asteraceae, has fleshy fruits with ornithochorous characteristics. However, no studies have confirmed the dispersion by birds or any other aspect of the reproductive biology of this unique Asteraceae. The present study aims to investigate the reproductive phenology, floral biology and breeding system and to identify the pollinators and seed dispersers of T. baccata. The study was carried out in a natural population located in a semideciduous forest (Viçosa, Minas Gerais State), southeastern Brazil. The reproductive cycle of T. baccata is annual and seasonal, related to precipitation, temperature and day length. The longevity of flowers and capitula depends on the performance of pollinators and dispersers. Hand pollination tests showed that the species is self-incompatible and therefore dependent on synchronous flowering and pollinator availability. Pollination occurred in the morning, in the period of pollen availability, and social bees were the major pollinator group. Seeds are dispersed by frugivorous birds, that swallow the ripe fruits and defecate viable seeds later. Our study confirmed the bird dispersal of Tilesia baccata seeds and also demonstrates that pollinator activity and fruit removal by birds influence the magnitude of activity and the intensity of flowering and fruiting.     

Sexual isolation in two bee-pollinated Costus (Costaceae)

Examining reproductive isolating barriers is essential for understanding processes of speciation. Sexual isolation has been shown to contribute to speciation in many sympatric taxa; however, its role in parapatric taxa with reduced interspecific gene flow is poorly understood. I investigated the extent of sexual isolation in two closely related Neotropical understory species, Costus allenii and C. villosissimus, that occur in adjacent habitats within flight distance of their shared pollinators, euglossine bees. Pollination arrays were used to test whether individual pollinators travel between species, to estimate the proportion of hetero- and conspecific pollen deposited on the stigmas, and to examine the proportion of hybrid progeny. In comparison to C. allenii, C. villosissimus produces flowers with larger labella, longer stamen–labellum distances, and longer styles. Pollinators visited both species but preferred C. villosissimus. This preference caused pollinator isolation in C. villosissimus. In C. allenii, the frequency of heterospecific pollinator transitions was not less common than that of conspecific transitions, but floral mechanical isolation greatly reduced the likelihood of heterospecific pollen deposition. The contribution of gametic isolation was not strong in either species. Based on data for pollinator isolation, floral mechanical isolation, and gametic isolation, it appears that sexual isolation is weak in C. allenii, restricting heterospecific gene flow by 25 %, but moderate in C. villosissimus, where gene flow from C. allenii is reduced by 70 %. Further research will estimate the magnitude of other isolation barriers to determine the relative contribution of sexual isolation to total isolation in this parapatric species pair.     

5种地黄花部综合特征与繁育系统的初步研究

生殖隔离是物种分化与延续的基础,地黄属植物是否存在生殖隔离仍不清楚。通过实地观测地黄属5个物种(天目地黄、湖北地黄、裂叶地黄、地黄和茄叶地黄)自然种群的花部形态、开花动态、花蜜体积、花蜜的糖浓度及其日变化、杂交指数、花粉-胚珠比等指标,结合人工授粉套袋,对地黄属植物的花部综合特征和繁育系统进行研究。结果显示:(1)地黄属植物的花为两性花,单花花期5～7 d,种群花期40～60 d;5种地黄在花序类型、花形态、花粉量、花粉-胚珠比等方面都存在差异,其中茄叶地黄的花粉完全败育。(2)5种地黄属植物的繁育系统属于异交,部分自交亲和,需要传粉者,不具有无融合生殖特性,地黄与茄叶地黄存在强烈营养繁殖。(3)5种地黄属植物的花朵基部有蜜腺可以产生糖浓度较高的花蜜,这也支持传粉者的存在,但除地黄确定为蜜蜂传粉外,其它地黄植物在野外并未观测到有效的传粉者,可能与地黄的散生特性、生境相互隔离以及传粉观测期气象条件恶劣有关。研究认为,5种地黄属植物较长的花期能有效弥补传粉者访问频率低的不足;除遗传屏障外,推测地黄属5个物种花展示方式的差异可能吸引不同的传粉者,加之地理、生态因素的作用导致了5种地黄属植物繁育系统的分化。