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1.
Nina Hobbhahn Steven D. Johnson Benny Bytebier Edward C. Yeung Lawrence D. Harder 《Annals of botany》2013,112(7):1303-1319
Background and Aims
The Orchidaceae have a history of recurring convergent evolution in floral function as nectar production has evolved repeatedly from an ancestral nectarless state. However, orchids exhibit considerable diversity in nectary type, position and morphology, indicating that this convergence arose from alternative adaptive solutions. Using the genus Disa, this study asks whether repeated evolution of floral nectaries involved recapitulation of the same nectary type or diversifying innovation. Epidermis morphology of closely related nectar-producing and nectarless species is also compared in order to identify histological changes that accompanied the gain or loss of nectar production.Methods
The micromorphology of nectaries and positionally equivalent tissues in nectarless species was examined with light and scanning electron microscopy. This information was subjected to phylogenetic analyses to reconstruct nectary evolution and compare characteristics of nectar-producing and nectarless species.Key Results
Two nectary types evolved in Disa. Nectar exudation by modified stomata in floral spurs evolved twice, whereas exudation by a secretory epidermis evolved six times in different perianth segments. The spur epidermis of nectarless species exhibited considerable micromorphological variation, including strongly textured surfaces and non-secreting stomata in some species. Epidermis morphology of nectar-producing species did not differ consistently from that of rewardless species at the magnifications used in this study, suggesting that transitions from rewardlessness to nectar production are not necessarily accompanied by visible morphological changes but only require sub-cellular modification.Conclusions
Independent nectary evolution in Disa involved both repeated recapitulation of secretory epidermis, which is present in the sister genus Brownleea, and innovation of stomatal nectaries. These contrasting nectary types and positional diversity within types imply weak genetic, developmental or physiological constraints in ancestral, nectarless Disa. Such functional convergence generated by morphologically diverse solutions probably also underlies the extensive diversity of nectary types and positions in the Orchidaceae. 相似文献2.
Background and Aims
Early ontogenetic stages of myrmecophytic plants are infrequently associated with ants, probably due to constraints on the production of rewards. This study reports for the first time the anatomical and histological limitations constraining the production of extrafloral nectar in young plants, and the implications that the absence of protective ants imposes for plants early during their ontogeny are discussed.Methods
Juvenile, pre-reproductive and reproductive plants of Turnera velutina were selected in a natural population and their extrafloral nectaries (EFNs) per leaf were quantified. The anatomical and morphological changes in EFNs during plant ontogeny were studied using scanning electron and light microscopy. Extrafloral nectar volume and sugar concentration were determined as well as the number of patrolling ants.Key Results
Juvenile plants were unable to secrete or contain nectar. Pre-reproductive plants secreted and contained nectar drops, but the highest production was achieved at the reproductive stage when the gland is fully cup-shaped and the secretory epidermis duplicates. No ants were observed in juvenile plants, and reproductive individuals received greater ant patrolling than pre-reproductive individuals. The issue of the mechanism of extrafloral nectar release in T. velutina was solved given that we found an anatomical, transcuticular pore that forms a channel-like structure and allows nectar to flow outward from the gland.Conclusions
Juvenile stages had no ant protection against herbivores probably due to resource limitation but also due to anatomical constraints. The results are consistent with the growth-differentiation balance hypothesis. As plants age, they increase in size and have larger nutrient-acquiring, photosynthetic and storage capacity, so they are able to invest in defence via specialized organs, such as EFNs. Hence, the more vulnerable juvenile stage should rely on other defensive strategies to reduce the negative impacts of herbivory. 相似文献3.
Background and Aims
Although most studies on plant defence strategies have focused on a particular defence trait, some plant species develop multiple defence traits. To clarify the effects of light on the development of multiple defence traits, the production of direct and indirect defence traits of young plants of Mallotus japonicus were examined experimentally under different light conditions.Methods
The young plants were cultivated under three light conditions in the experimental field for 3 months from May to July. Numbers of ants and pearl bodies on leaves in July were examined. After cultivation, the plants were collected and the developments of trichomes and pellucid dots, and extrafloral nectaries (EFNs) on the leaves were examined. On plants without nectar-collecting insects, the size of EFNs and the volume of extrafloral nectar secreted from the EFNs were examined.Key results
Densities of trichomes and pellucid dots did not differ significantly among the plants under the different light conditions, suggesting that the chemical and physical defences function under both high and low light availability. The number of EFNs on the leaves did not differ significantly among the plants under the different light conditions, but there appeared to be a trade-off between the size of EFNs and the number of pearl bodies; the largest EFNs and the smallest number of pearl bodies were found under high light availability. EFN size was significantly correlated with the volume of extrafloral nectar secreted for 24 h. The number of ants on the plants was smaller under low light availability than under high and moderate light availability.Conclusions
These results suggest that direct defence traits function regardless of light conditions, but light conditions affected the development of indirect defence traits. 相似文献4.
Pedro Adrián Aguilar-Rodríguez M. Cristina MacSwiney G. Thorsten Kr?mer José G. García-Franco Anina Knauer Michael Kessler 《Annals of botany》2014,113(6):1047-1055
Background and Aims
Bromeliaceae is a species-rich neotropical plant family that uses a variety of pollinators, principally vertebrates. Tillandsia is the most diverse genus, and includes more than one-third of all bromeliad species. Within this genus, the majority of species rely on diurnal pollination by hummingbirds; however, the flowers of some Tillandsia species show some characteristics typical for pollination by nocturnal animals, particularly bats and moths. In this study an examination is made of the floral and reproductive biology of the epiphytic bromeliad Tillandsia macropetala in a fragment of humid montane forest in central Veracruz, Mexico.Methods
The reproductive system of the species, duration of anthesis, production of nectar and floral scent, as well as diurnal and nocturnal floral visitors and their effectiveness in pollination were determined.Key Results
Tillandsia macropetala is a self-compatible species that achieves a higher fruit production through outcrossing. Nectar production is restricted to the night, and only nocturnal visits result in the development of fruits. The most frequent visitor (75 % of visits) and the only pollinator of this bromeliad (in 96 % of visits) was the nectarivorous bat Anoura geoffroyi (Phyllostomidae: Glossophaginae).Conclusions
This is the first report of chiropterophily within the genus Tillandsia. The results on the pollination biology of this bromeliad suggest an ongoing evolutionary switch from pollination by birds or moths to bats. 相似文献5.
Background and Aims
Determining the sources of variation in floral morphology is crucial to understanding the mechanisms underlying Angiosperm evolution. The selection of floral and reproductive traits is influenced by the plant''s abiotic environment, florivores and pollinators. However, evidence that variations in floral traits result from mutualistic interactions with insects other than pollinators is lacking in the published literature and has rarely been investigated. We aimed to determine whether the association with either Camponotus femoratus or Pachycondyla goeldii (both involved in seed dispersal and plant protection) mediates the reproductive traits and allocation of Aechmea mertensii, an obligatory ant-garden tank-bromeliad, differently.Methods
Floral and reproductive traits were compared between the two A. mertensii ant-gardens. The nitrogen flux from the ants to the bromeliads was investigated through experimental enrichments with stable isotopes (15N).Key Results
Camponotus femoratus-associated bromeliads produced inflorescences up to four times longer than did P. goeldii-associated bromeliads. Also, the numbers of flowers and fruits were close to four times higher, and the number of seeds and their mass per fruit were close to 1·5 times higher in C. femoratus than in P. goeldii-associated bromeliads. Furthermore, the 15N-enrichment experiment showed that C. femoratus-associated bromeliads received more nitrogen from ants than did P. goeldii-associated bromeliads, with subsequent positive repercussions on floral development. Greater benefits were conferred to A. mertensii by the association with C. femoratus compared with P. goeldii ants.Conclusions
We show for the first time that mutualistic associations with ants can result in an enhanced reproductive allocation for the bromeliad A. mertensii. Nevertheless, the strength and direction of the selection of floral and fruit traits change based on the ant species and were not related to light exposure. The different activities and ecological preferences of the ants may play a contrasting role in shaping plant evolution and speciation. 相似文献6.
Background and Aims
Abolboda (Xyridaceae) belongs to the Poales, a predominantly wind-pollinated order whose phylogeny has been widely studied in recent years. The reproductive biology of Abolboda pulchella and A. poarchon was studied to determine the main pollination system of these species, providing the first experimental data on reproduction in the Xyridaceae.Methods
A field study was conducted, including observations on the morphology and biology of the flowers, insect visits and pollinator behaviour. Experimental pollination treatments were performed to assess agamospermy, spontaneous self-pollination and self-compatibility. Pollination success was determined by pollen tube growth, and reproductive success was assessed by fruit- and seed-set.Key Results
Abolboda pulchella and A. poarchon were pollinated by Apidae, Megachilidae and Halictidae bees. The floral resources were pollen and nectar that was produced by stylar appendages, an uncommom nectary type for monocotyledons. The species were self-compatible, and pollen tube growth from self-pollen was similar to that of cross-pollen. However, herkogamy prevented spontaneous selfing, rendering the plants dependent on the pollinator''s activity. There was no production of seeds by agamospermy.Conclusions
Melittophily is the main pollination system of these two Abolboda species. Nectar production was first recorded here for Xyridaceae, and along with self-compatibility, herkogamy and bee pollination, is an informative characteristic that can be used in future phylogenetic analyses of the family as well as Poales. 相似文献7.
Patrizia Trifil�� Fabio Raimondo Maria Assunta Lo Gullo Andrea Nardini Sebastiano Salleo 《Annals of botany》2010,106(2):333-341
Background and Aims
The hydraulic architecture and water relations of fruits and leaves of Capsicum frutescens were measured before and during the fruiting phase in order to estimate the eventual impact of xylem cavitation and embolism on the hydraulic isolation of fruits and leaves before maturation/abscission.Methods
Measurements were performed at three different growth stages: (1) actively growing plants with some flowers before anthesis (GS1), (2) plants with about 50 % fully expanded leaves and immature fruits (GS2) and (3) plants with mature fruits and senescing basal leaves (GS3). Leaf conductance to water vapour as well as leaf and fruit water potential were measured. Hydraulic measurements were made using both the high-pressure flow meter (HPFM) and the vacuum chamber (VC) technique.Key Results
The hydraulic architecture of hot pepper plants during the fruiting phase was clearly addressed to favour water supply to growing fruits. Hydraulic measurements revealed that leaves of GS1 plants as well as leaves and fruit peduncles of GS2 plants were free from significant xylem embolism. Substantial increases in leaf petiole and fruit peduncle resistivity were recorded in GS3 plants irrespective of the hydraulic technique used. The higher fraction of resistivity measured using the VC technique compared with the HPFM technique was apparently due to conduit embolism.Conclusions
The present study is the first to look at the hydraulics of leaves and fruits during growth and maturation through direct, simultaneous measurements of water status and xylem efficiency of both plant regions at different hours of the day. 相似文献8.
Background and Aims
The mechanisms of floral nectar production in buckwheat (Fagopyrum esculentum, Polygonaceae), a distylous pseudo-cereal, have received relatively little attention, prompting an investigation of the factors that regulate this process. The aim was to perform a refined study of the structures that secrete nectar and of the internal and external parameters influencing nectar volumes and sugar concentrations.Methods
In order to control environmental parameters, plants were cultivated in growth rooms under controlled conditions. The structure of nectaries was studied based on histological sections from flowers and flower buds. Nectar was extracted using glass micropipettes and the sugar concentration was measured with a hand refractometer. Sugar concentration in the phloem sap was measured using the anthrone method. To test the influence of photosynthesis on nectar production, different light and defoliation treatments were applied.Key Results
Unicellular trichomes were located in the epidermis at the ventral part of eight nectary glands situated on the flower receptacle alternately with stamens. Vascular bundles consisting of both phloem and xylem were identified at the boundary between a multilayered nectary parenchyma and a sub-nectary parenchyma with chloroplasts. A higher volume of nectar in thrum morphs was observed. No other difference was found in morphology or in sugar supply to inflorescences between morphs. Nectar secretion was strongly influenced by plant age and inflorescence position. Nectar volumes were higher in the upper inflorescences and during the flowering peak. Light had a dual role, (1) acting directly on reproductive structures to trigger flower opening, which conditions nectar secretion, and (2) stimulating photosynthetic activity, which regulates nectar accumulation in open flowers.Conclusions
In buckwheat, nectar is secreted by trichomes and probably proceeds, at least in part, from phloem sap. Nectar secretion is strongly influenced by floral morph type, plant age, inflorescence position and light.Key words: Buckwheat, distyly, Fagopyrum esculentum, inflorescence position, morph comparisons, nectary histology, nectar sugar concentration, nectar volume, light intensity, organ biomass, phloem sap, plant age 相似文献9.
Brigitte Marazzi Elena Conti Michael J. Sanderson Michelle M. McMahon Judith L. Bronstein 《Annals of botany》2013,111(6):1263-1275
Background and Aims
Plants display a wide range of traits that allow them to use animals for vital tasks. To attract and reward aggressive ants that protect developing leaves and flowers from consumers, many plants bear extrafloral nectaries (EFNs). EFNs are exceptionally diverse in morphology and locations on a plant. In this study the evolution of EFN diversity is explored by focusing on the legume genus Senna, in which EFNs underwent remarkable morphological diversification and occur in over 80 % of the approx. 350 species.Methods
EFN diversity in location, morphology and plant ontogeny was characterized in wild and cultivated plants, using scanning electron microscopy and microtome sectioning. From these data EFN evolution was reconstructed in a phylogenetic framework comprising 83 Senna species.Key Results
Two distinct kinds of EFNs exist in two unrelated clades within Senna. ‘Individualized’ EFNs (iEFNs), located on the compound leaves and sometimes at the base of pedicels, display a conspicuous, gland-like nectary structure, are highly diverse in shape and characterize the species-rich EFN clade. Previously overlooked ‘non-individualized’ EFNs (non-iEFNs) embedded within stipules, bracts, and sepals are cryptic and may represent a new synapomorphy for clade II. Leaves bear EFNs consistently throughout plant ontogeny. In one species, however, early seedlings develop iEFNs between the first pair of leaflets, but later leaves produce them at the leaf base. This ontogenetic shift reflects our inferred diversification history of iEFN location: ancestral leaves bore EFNs between the first pair of leaflets, while leaves derived from them bore EFNs either between multiple pairs of leaflets or at the leaf base.Conclusions
EFNs are more diverse than previously thought. EFN-bearing plant parts provide different opportunities for EFN presentation (i.e. location) and individualization (i.e. morphology), with implications for EFN morphological evolution, EFN–ant protective mutualisms and the evolutionary role of EFNs in plant diversification. 相似文献10.
Background and Aims
In complex communities, organisms often form mutualisms with multiple different partners simultaneously. Non-additive effects may emerge among species linked by these positive interactions. Ants commonly participate in mutualisms with both honeydew-producing insects (HPI) and their extrafloral nectary (EFN)-bearing host plants. Consequently, HPI and EFN-bearing plants may experience non-additive benefits or costs when these groups co-occur. The outcomes of these interactions are likely to be influenced by variation in preferences among ants for honeydew vs. nectar. In this study, a test was made for non-additive effects on HPI and EFN-bearing plants resulting from sharing exotic ant guards. Preferences of the dominant exotic ant species for nectar vs. honeydew resources were also examined.Methods
Ant access, HPI and nectar availability were manipulated on the EFN-bearing shrub, Morinda citrifolia, and ant and HPI abundances, herbivory and plant growth were assessed. Ant-tending behaviours toward HPI across an experimental gradient of nectar availability were also tracked in order to investigate mechanisms underlying ant responses.Key Results
The dominant ant species, Anoplolepis gracilipes, differed from less invasive ants in response to multiple mutualists, with reductions in plot-wide abundances when nectar was reduced, but no response to HPI reduction. Conversely, at sites where A. gracilipes was absent or rare, abundances of less invasive ants increased when nectar was reduced, but declined when HPI were reduced. Non-additive benefits were found at sites dominated by A. gracilipes, but only for M. citrifolia plants. Responses of HPI at these sites supported predictions of the non-additive cost model. Interestingly, the opposite non-additive patterns emerged at sites dominated by other ants.Conclusions
It was demonstrated that strong non-additive benefits and costs can both occur when a plant and herbivore share mutualist partners. These findings suggest that broadening the community context of mutualism studies can reveal important non-additive effects and increase understanding of the dynamics of species interactions. 相似文献11.
Background
Plants in over one hundred families in habitats worldwide bear extrafloral nectaries (EFNs). EFNs display a remarkable diversity of evolutionary origins, as well as diverse morphology and location on the plant. They secrete extrafloral nectar, a carbohydrate-rich food that attracts ants and other arthropods, many of which protect the plant in return. By fostering ecologically important protective mutualisms, EFNs play a significant role in structuring both plant and animal communities. And yet researchers are only now beginning to appreciate their importance and the range of ecological, evolutionary and morphological diversity that EFNs exhibit.Scope
This Highlight features a series of papers that illustrate some of the newest directions in the study of EFNs. Here, we introduce this set of papers by providing an overview of current understanding and new insights on EFN diversity, ecology and evolution. We highlight major gaps in our current knowledge, and outline future research directions.Conclusions
Our understanding of the roles EFNs play in plant biology is being revolutionized with the use of new tools from developmental biology and genomics, new modes of analysis allowing hypothesis-testing in large-scale phylogenetic frameworks, and new levels of inquiry extending to community-scale interaction networks. But many central questions remain unanswered; indeed, many have not yet been asked. Thus, the EFN puzzle remains an intriguing challenge for the future. 相似文献12.
Evelyn Villagra Carola Campos-Hernandez Pablo Cáceres Gustavo Cabrera Yamilé Bernardo Ariel Arencibia Basilio Carrasco Peter DS Caligari José Pico Rolando García-Gonzales 《Biological research》2014,47(1)
Background
For the first time, a morphometric characterization of chaura (Gaultheria pumila) fruits has been conducted between natural populations growing in the Villarrica National Park, Araucania Region, Chile. Chaura is a native Ericaceae from Chile that produces aromatic and tasty fruits which could be of agricultural interest.Results
To influence the decision for a further domestication of G. pumila, both the fruit sizes (indicator of productivity) and the nutritional properties of the fruits have been determined from different subpopulations. Samples were a total of 74 plants and 15 fruits per plant which were randomly harvested following its natural distribution around the Villarrica volcano. Altogether, fresh weight, shape, color, diameter in the pole and the equatorial dimensions were determined as phenotypic traits of the G. pumila fruits. Meanwhile the total soluble solids, anthocyanin and pectin contents were calculated as nutritional traits of the Chaura fruits. Results showed a high phenotypic diversity between the sampled population with three main fruit shapes and three predominant colors. The round shapes were the most abundant, whereas a significant correlation was found among fruit size with weight and color. The highest fresh weight (597.3 mg), pole diameter (7.1 mm) and equatorial diameter (6.5 mm) were estimated in the pink color fruits.Conclusions
The total amount of anthocyanin was higher in red fruits, while the maximum pectin content was obtained in the round white fruits. Overall results must pave the way for a further domestication and introduction of the Chaura species in the agro-productive system in Chile. 相似文献13.
Background and Aims
Due in part to biophysical sized-related constraints, insects unlike vertebrates are seldom expected to act as primary seed dispersers via ingestion of fruits and seeds (endozoochory). The Mediterranean parasitic plant Cytinus hypocistis, however, possesses some characteristics that may facilitate endozoochory by beetles. By combining a long-term field study with experimental manipulation, we tested whether C. hypocistis seeds are endozoochorously dispersed by beetles.Methods
Field studies were carried out over 4 years on six populations in southern Spain. We recorded the rate of natural fruit consumption by beetles, the extent of beetle movement, beetle behaviour and the relative importance of C. hypocistis fruits in beetle diet.Key Results
The tenebrionid beetle Pimelia costata was an important disperser of C. hypocistis seeds, consuming up to 17·5 % of fruits per population. Forty-six per cent of beetles captured in the field consumed C. hypocistis fruits, with up to 31 seeds found in individual beetle frass. An assessment of seeds following passage through the gut of beetles indicated that seeds remained intact and viable and that the proportion of viable seeds from beetle frass was not significantly different from that of seeds collected directly from fruits.Conclusions
A novel plant–animal interaction is revealed; endozoochory by beetles may facilitate the dispersal of viable seeds after passage through the gut away from the parent plant to potentially favourable underground sites offering a high probability of germination and establishment success. Such an ecological role has until now been attributed only to vertebrates. Future studies should consider more widely the putative role of fruit and seed ingestion by invertebrates as a dispersal mechanism, particularly for those plant species that possess small seeds. 相似文献14.
15.
Floral traits mediate the vulnerability of aloes to pollen theft and inefficient pollination by bees
Background and Aims
Pollen-collecting bees are among the most important pollinators globally, but are also the most common pollen thieves and can significantly reduce plant reproduction. The pollination efficiency of pollen collectors depends on the frequency of their visits to female(-phase) flowers, contact with stigmas and deposition of pollen of sufficient quantity and quality to fertilize ovules. Here we investigate the relative importance of these components, and the hypothesis that floral and inflorescence characteristics mediate the pollination role of pollen collection by bees.Methods
For ten Aloe species that differ extensively in floral and inflorescence traits, we experimentally excluded potential bird pollinators to quantify the contributions of insect visitors to pollen removal, pollen deposition and seed production. We measured corolla width and depth to determine nectar accessibility, and the phenology of anther dehiscence and stigma receptivity to quantify herkogamy and dichogamy. Further, we compiled all published bird-exclusion studies of aloes, and compared insect pollination success with floral morphology.Key Results
Species varied from exclusively insect pollinated, to exclusively bird pollinated but subject to extensive pollen theft by insects. Nectar inaccessibility and strong dichogamy inhibited pollination by pollen-collecting bees by discouraging visits to female-phase (i.e. pollenless) flowers. For species with large inflorescences of pollen-rich flowers, pollen collectors successfully deposited pollen, but of such low quality (probably self-pollen) that they made almost no contribution to seed set. Indeed, considering all published bird-exclusion studies (17 species in total), insect pollination efficiency varied significantly with floral shape.Conclusions
Species-specific floral and inflorescence characteristics, especially nectar accessibility and dichogamy, control the efficiency of pollen-collecting bees as pollinators of aloes. 相似文献16.
Background and Aims
Floral secretions are common in Bulbophyllum Thouars, and the labella of a number of Asian species are said to produce secretions rich in lipids that act as food rewards for insect pollinators. Although some of these reports are based on simple histochemical tests, a much greater number are anecdotal and, hitherto, neither the ultrastructure of the labellum nor the secretory process has been investigated in detail. Furthermore, sophisticated histochemical approaches have generally not been applied. Here, both the labellar structure and the secretory process are investigated for four species of Asian Bulbophyllum sect. Racemosae Benth. & Hook. f., namely Bulbophyllum careyanum (Hook.) Spreng., B. morphologorum Kraenzl., B. orientale Seidenf. and B. wangkaense Seidenf., and compared with those of unequivocal lipid-secreting orchids.Methods
Labellar, secretory tissue was investigated using light microscopy, scanning electron microscopy, transmission electron microscopy and histochemistry.Key Results
The adaxial median longitudinal groove of the labellum contained secretory tissue comprising palisade-like epidermal cells, similar to those of certain lipid-secreting Oncidiinae Benth. However, these cells and their secretions gave positive results mainly for protein and mucilage, and their organelle complement was consistent with that of cells involved in protein and mucilage synthesis. Sub-cuticular accumulation of secretion resulted in cuticular distension and blistering. The sub-epidermal layer of isodiametric parenchyma contained starch and, like the epidermal cells, ultrastructure consistent with mucilage synthesis. Lipids were mainly confined to the cuticle, and hardly any intracellular lipid droplets were observed.Conclusions
It is proposed that mucilage is produced by dictyosomes present in the palisade-like epidermal cells. Mucilage precursors may also be produced by these same organelles in sub-epidermal cells and are thought to pass along the symplast via plasmodesmata into the adjoining palisade-like secretory cells, which contain abundant arrays of rough endoplasmic reticulum. Here, they become chemically modified and form a protein-rich, mucilaginous secretion that, following vesicle-mediated transport across the cytoplasm, traverses the cell wall and accumulates in blisters formed from the distended cuticle. Rupture of these blisters releases the secretion onto the labellar surface. However, in certain species, there is some evidence that the secretion may traverse the cuticle via cuticular pores, and micro-channels may permit the passage of fragrance. Hydrolysis of sub-epidermal starch probably generates the carbohydrate and, together with mitochondria, much of the energy required for the secretory process. This anatomical organization resembles that found in certain lipid-secreting, Neotropical species of Bulbophyllum and Oncidiinae, but since the chemical composition of their secretions is different, and these taxa occur on a separate continent and have different insect pollinators, parallelism of floral anatomy is likely. 相似文献17.
Background and Aims
Plants are adapted for rodent pollination in diverse and intricate ways. This study explores an extraordinary example of these adaptations in the pincushion Leucospermum arenarium (Proteaceae) from South Africa.Methods
Live trapping and differential exclusion experiments were used to test the role of rodents versus birds and insects as pollinators. To explore the adaptive significance of geoflory, inflorescences were raised above ground level and seed production was compared. Captive rodents and flowers with artificial stigmas were used to test the effect of grooming on the rate of pollen loss. Microscopy, nectar composition analysis and manipulative experiments were used to investigate the bizarre nectar production and transport system.Key Results
Differential exclusion of rodents, birds and insects demonstrated the importance of rodents in promoting seed production. Live trapping revealed that hairy-footed gerbils, Gerbillurus paeba, and striped field mice, Rhabdomys pumilio, both carried L. arenarium pollen on their forehead and rostrum, but much larger quantities ended up in faeces as a result of grooming. Terrarium experiments showed that grooming exponentially diminished the pollen loads that they carried. The nectar of L. arenarium was found to be unusually viscous and to be presented in a novel location on the petal tips, where rodents could access it without destroying the flowers. Nectar was produced inside the perianth, but was translocated to the petal tips via capillary ducts. In common with many other rodent-pollinated plants, the flowers are presented at ground level, but when raised to higher positions seed production was not reduced, indicating that selection through female function does not drive the evolution of geoflory.Conclusions
Despite the apparent cost of pollen lost to grooming, L. arenarium has evolved remarkable adaptations for rodent pollination and provides the first case of this pollination system in the genus. 相似文献18.
Background and Aims
The Borasseae form a highly supported monophyletic clade in the Arecaceae–Coryphoideae. The fruits of Coryphoideae are small, drupaceous with specialized anatomical structure of the pericarp and berries. The large fruits of borassoid palms contain massive pyrenes, which develop from the middle zone of the mesocarp. The pericarp structure and mode of its development in Borasseae are similar to those of Eugeissona and Nypa. A developmental carpological study of borassoid palms will allow us to describe the process of pericarp development and reveal the diagnostic fruit features of borassoid palms, determine the morphogenetic fruit type in Borasseae genera, and describe similarities in fruit structure and pericarp development with other groups of palms.Methods
The pericarp anatomy was studied during development with light microscopy based on the anatomical sections of fruits of all eight Borasseae genera.Key Results
The following general features of pericarp structure in Borasseae were revealed: (1) differentiation of the pericarp starts at early developmental stages; (2) the exocarp is represented by a specialized epidermis; (3) the mesocarp is extremely multilayered and is differentiated into several topographical zones – a peripheral parenchymatous zone(s) with scattered sclerenchymatous elements and vascular bundles, a middle zone (the stony pyrene comprising networks of elongated sclereids and vascular bundles) and an inner parenchymatous zone(s); (4) differentiation and growth of the pyrene tissue starts at early developmental stages and ends long before maturation of the seed; (5) the inner parenchymatous zone(s) of the mesocarp is dramatically compressed by the mature seed; (6) the endocarp (unspecialized epidermis) is not involved in pyrene formation; and (7) the spermoderm is multilayered in Hyphaeninae and obliterated in Lataniinae.Conclusions
The fruits of Borasseae are pyrenaria of Latania-type. This type of pericarp differentiation is also found only in Eugeissona and Nypa. The fruits of other Coryphoideae dramatically differ from Borasseae by the pericarp anatomical structure and the mode of its development. 相似文献19.
Background and Aims
Natural variation in fruit and seed set may be explained by factors that affect the composition of pollen grains on stigmas. Self-incompatible species require compatible outcross pollen grains to produce seeds. The siring success of outcross pollen grains, however, can be hindered if self (or other incompatible) pollen grains co-occur on stigmas. This study identifies factors that determine fruit set in Phlox hirsuta, a self-sterile endangered species that is prone to self-pollination, and its associated fitness costs.Methods
Multiple linear regressions were used to identify factors that explain variation in percentage fruit set within three of the five known populations of this endangered species. Florivorous beetle density, petal colour, floral display size, local conspecific density and pre-dispersal seed predation were quantified and their effects on the ability of flowers to produce fruits were assessed.Key Results
In all three populations, percentage fruit set decreased as florivorous beetle density increased and as floral display size increased. The effect of floral display size on fruit set, however, often depended on the density of nearby conspecific plants. High local conspecific densities offset – even reversed – the negative effects of floral display size on percentage fruit set. Seed predation by mammals decreased fruit set in one population.Conclusions
The results indicate that seed production in P. hirsuta can be maximized by selectively augmenting populations in areas containing isolated large plants, by reducing the population sizes of florivorous beetles and by excluding mammals that consume unripe fruits. 相似文献20.