Submarine pollination in the marine angiosperm Zostera marina (Zosteraceae). II. Pollen transport in flow fields and capture by stigmas

Flow chamber observations of the filamentous pollen of Zostera marina L. (Potamogetonales) revealed that pollen rotated and moved toward inflorescences where they were captured by stigmas. The mechanics of this abiotic pollination process were examined and found to be related to the flow environment around emergent flowers. The translational movement of pollen was imparted by the advection of the fluid (e.g., pollen kinetic energy, K, ranged from 0.8 x 10-14 to 2.4 x 10-14 J, and the average K of the fluid was _ 0.7 x 10-14 J), while the rotational motion was imparted by the fluid shear stress (tau) within the velocity gradient (e.g., pollen shear stress, sigmat = omegamu where omega is the rotational velocity and mu is the dynamic viscosity, ranged from 3.4 x 10-4 to 26 x 10-4 Pa, and the average fluid shear stress was tau _ 10 x 10-4 Pa; Ackerman, 1997, American Journal of Botany 84: 1099-1109). These results indicate that there is a greater potential for pollination by filamentous pollen relative to spherical pollen. Functionally, while spherical pollen needs to be directly upstream from stigmas to be captured, filamentous pollen need only be in the vicinity of inflorescences and flowers to be captured by stigmas. Thus, in addition to direct interception on stigmas, filamentous pollen can be captured while they rotate past flowers or when they are redirected through the velocity gradient towards flowers. Filamentous pollen is an adaptation to submarine pollination in seagrasses.     

Diffusivity in a marine macrophyte canopy: implications for submarine pollination and dispersal

The dispersion and capture of differently shaped particles within a Zostera marina L. (eelgrass; Zosteraceae) bed were examined to understand submarine pollination and other dispersals. During periods of moderate flow in the canopy, the capture rate of "spherical" (the shape of ancestral pollen) and "filamentous" (the shape of eelgrass pollen) particles was greater for particles released at the top of the canopy (3.07 and 4.53% × 10(-5) cm(-2) of collector; i.e., percentage of particles captured normalized to collector area) and greater for filamentous than for spherical particles (4.51% × 10(-5) cm(-2) vs. 2.01% × 10(-5) cm(-2)). Estimates of the horizontal P (Joseph-Sendner diffusion velocity) and the vertical diffusivity (Gaussian K) of filamentous particles were small (P ≈ 4 × 10(-4) m/s; K ≈ 10(-4) m(2)/s) compared to theoretical values that do not consider plant canopies. These findings support the concept that eelgrass canopies modify the fluid dynamics (i.e., reduced turbulent mixing) within their canopies. These results indicate that 1000-10?000 Z. marina pollen are required to pollinate a single flower. Similarly, it was estimated that under some conditions, the probability of particle impaction on eelgrass vegetation approaches certainty. These results provide insight into the evolution of filamentous pollen and submarine pollination, as well as dispersal and other mass transport phenomena within macrophyte canopies.     

A ballistic pollen dispersal system influences pollination success and fruit‐set pattern in pollinator‐excluded environments for the endangered species Synaphea stenoloba (Proteaceae)

The critically endangered Synaphea stenoloba (Proteaceae) has numerous scentless flowers clustered in dense inflorescences and deploys a ballistic pollen ejection mechanism to release pollen. We examined the hypothesis that active pollen ejection and flowering patterns within an inflorescence influence the reproductive success (i.e. fruit formation) of individual flowers within or among inflorescences of S. stenoloba in a pollinator‐excluded environment. Our results showed that: (1) no pollen grains were observed deposited on the stigma of their own flower after the pollen ejection system was manually activated, indicating self‐pollination within an individual flower is improbable in S. stenoloba; (2) fruit set in the indoor open pollination treatment and the inflorescence‐closed pollination treatment indicated that S. stenoloba is self‐compatible and pollen ejection can potentially result in inter‐floral pollination success; (3) fruit set in the inflorescence‐closed pollination treatment was significantly lower than that of indoor open pollination, indicating within‐ and between‐flower pollination events in an inflorescence are most likely limited, with pollination between inflorescences providing the highest reproductive opportunity; and (4) analysis of the spatial distribution of cumulative fruit set on inflorescences showed that pollen could reach any flower within an inflorescence and there was no functional limitation on seed set among flowers located at various positions within the inflorescence. These data suggest that the pollen ejection mechanism in S. stenoloba can enhance inter‐plant pollination in pollinator‐excluded environments and may suggest adaptation to pollinator scarcity attributable to habitat disturbance or competition for pollinators in a diverse flora. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170 , 59–68.     

Reproductive structures of an extinct platanoid from the early Cretaceous (latest Albian) of eastern North America

Two new species of platanoid reproductive structure are described from the Bull Mountain locality in the Patapsco Formation (Potomac Group) of northeastern Maryland, USA. Pistillate inflorescences and infructescences (Platanocarpus elkneckensis sp. nov.) consist of flowers and fruits in sessile globose heads that are borne on an elongate axis. Individual pistillate flowers consist of five free carpels surrounded by prominent tepals. Staminate inflorescences, flowers and isolated stamens are assigned to Hamatia elkneckensis gen. et sp. nov. Staminate flowers are borne in a globose head with a small number of stamens (five?) per flower. Stamens consist of very short filaments, long anthers with strongly valvate dehiscence and an apically expanded connective. The connective expansion is frequently very well-developed, hook-like and extends down the ventral surface of the stamen. Anthers contain small, tricolporate, reticulate pollen. Association evidence, similarity of inflorescence structure and the occurrence of Hamatia-type pollen on flowers, carpels and fruits of Platanocarpus elkneckensis suggests that the staminate and pistillate material was produced by a single species of plant. The “Hamatia-plant” provides further evidence of pentamerous floral structure in mid-Cretaceous platanoids and documents the occurrence of unequivocal tricolporate pollen in the platanoid complex.     

Male-biased sex allocation in late-blooming flowers driven by resource limitation in the clonal perennial Aconitum kusnezoffii (Ranunculaceae)

Flowering phenology and clonal growth are known to affect resource and pollen availability, and therefore select for adaptive or constrained sex allocation strategies to some degree. However, the consequences of temporal sex allocation patterns for reproductive fitness across the flower, inflorescence, and genet levels have rarely been examined. Moreover, experimental tests of the underlying regulatory mechanisms are scarce. We examined the association of flowering phenology and inflorescence position with temporal sex allocation and reproductive success in the protandrous perennial clonal herb, Aconitum kusnezoffii, over four consecutive growing seasons by examining more than 39 000 flowers. We also conducted controlled experiments to test the effects of resource and pollen limitation on the female reproductive success of lateral inflorescences. We found that some male functions were positively correlated with flowering phenology, whereas female reproductive success was negatively correlated with flowering phenology and inflorescence position. Lateral inflorescences invested more in male function than terminal inflorescences and therefore yielded fewer and smaller seeds. Resource limitation may serve as the key mechanism underlying this differentiated pattern. Decreased female reproductive success was consistently observed at the flower and inflorescence levels as flowering occurred later in the growth season. Late-blooming lateral inflorescences specialized in the male function, and their female reproductive success was constrained by early-blooming terminal inflorescences. This might be the first attempt to systematically demonstrate sex allocation strategy differentiation in a protandrous plant species at the inflorescence level. In addition, our study provides empirical evidence of dichogamy selecting for specialized sex allocation strategies among inflorescences.     

FLORAL DISPLAY IN PHYLA INCISA: CONSEQUENCES FOR MALE AND FEMALE REPRODUCTIVE SUCCESS

The inflorescences of Phyla incisa consist of flowers in two phases: younger, nectar-containing flowers that have yellow corolla throats and older, nectar-lacking flowers that have dark purple corolla throats. Observations of pollinator visitation patterns to both natural and manipulated inflorescences were made to determine the role of each flower phase in pollinator attraction. The effect of older-phase flowers on male and female reproductive success was determined by comparing stigmatic pollen loads and estimates of pollen removal from inflorescences having different numbers of these flowers. The pollinators of Phyla selected larger inflorescences more often than expected based upon the size distribution of inflorescences available to them. Both younger- and older-phase flowers contributed to the attraction of pollinators, but the latter were less effective in this function. The presence of older-phase flowers significantly increased the visitation rate to inflorescences and the amount of pollen removed but had little effect on pollen deposition on stigmas. The lack of correspondence between pollen deposition and pollinator-visitation rate was not due to stigma saturation, since stigma loads varied greatly. The data indicate that the deposition of pollen on stigmas in this species is a relatively stochastic process, whereas pollen removal from inflorescences occurs at a much more regular rate. Old-phase flower retention appears to contribute to reproductive success through increased pollen donation when pollinator activity is high and may also increase the probability of seed set when pollinators are rare.     

Is Floral Longevity Influenced by Reproductive Costs and Pollination Success in Cohniella ascendens (Orchidaceae)?

Background and Aims

Although studies have shown that pollen addition and/or removal decreases floral longevity, less attention has been paid to the relationship between reproductive costs and floral longevity. In addition, the influence of reproductive costs on floral longevity responses to pollen addition and/or removal has not yet been evaluated. Here, the orchid Cohniella ascendens is used to answer the following questions. (a) Does experimental removal of flower buds in C. ascendens increase flower longevity? (b) Does pollen addition and/or removal decrease floral longevity, and does this response depend on plant reproductive resource status?

Methods

To study the effect of reproductive costs on floral longevity 21 plants were selected from which we removed 50 % of the developing flower buds on a marked inflorescence. Another 21 plants were not manipulated (controls). One month later, one of four flowers on each marked inflorescence received one of the following pollen manipulation treatments: control, pollinia removal, pollination without pollinia removal or pollination with pollinia removal. The response variable measured was the number of days each flower remained open (i.e. longevity).

Key Results

The results showed significant flower bud removal and pollen manipulation effects on floral longevity; the interaction between these two factors was not significant. Flowers on inflorescences with previously removed flower buds remained open significantly longer than flowers on control inflorescences. On the other hand, pollinated flowers closed much faster than control and removed-pollinia flowers, the latter not closing significantly faster than control flowers, although this result was marginal.

Conclusions

The results emphasize the strong relationship between floral longevity and pollination in orchids, as well as the influence of reproductive costs on the former.Key words: Cohniella ascendens, floral longevity, flower bud removal, pollination, pollinia removal, reproductive costs     

Stress relaxation of porcine gluteus muscle subjected to sudden transverse deformation as related to pressure sore modeling

Computational studies of deep pressure sores (DPS) in skeletal muscles require information on viscoelastic constitutive behavior of muscles, particularly when muscles are loaded transversally as during bone-muscle interaction in sitting and lying immobilized patients. In this study, we measured transient shear moduli G(t) of fresh porcine muscles in vitro using the indentation method. We employed a custom-made pneumatic device that allowed rapid (2000 mms) 4 mm indentations. We tested 8 gluteus muscles, harvested from 5 adult pigs. Each muscle was indented transversally (perpendicularly to the direction of fibers) at 3 different sites, 7 times per site, to obtain nonpreconditioned (NPC) and preconditioned (PC) G(t) data. Short-term (GS) and long-term (GL) shear moduli were obtained directly from experiments. We further fitted measured G(t) data to a biexponential equation G(t) = G1 x exp(-t/tau1)+ G2 x exp(-t/tau2) + Ginfinity, which provided good fit, visually and in terms of the correlation coefficients. Typically, plateau of the stress relaxation curves (defined as 10% difference from final GL) was evident approximately 20 s after indentation. Short-term shear moduli GS (mean NPC: 8509 Pa, PC: 5711 Pa) were greater than long-term moduli GL (NPC: 609 Pa, PC: 807 Pa) by about an order of magnitude. Statistical analysis of parameters showed that only G2 was affected by preconditioning, while GL, GS, Ginfinity, tau1, tau2, and G1 properties were unaffected. Since DPS develop over time scales of minutes to hours, but most stress relaxation occurs within approximately 20 s, the most relevant property for computational modeling is GL (mean approximately 700 Pa), which is, conveniently, unaffected by preconditioning.     

Pollination mutualism between Alocasia macrorrhizos (Araceae) and two taxonomically undescribed Colocasiomyia species (Diptera: Drosophilidae) in Sabah, Borneo

Two taxonomically undescribed Colocasiomyia species were discovered from inflorescences of Alocasia macrorrhizos in Kota Kinabalu City, Sabah, Borneo, Malaysia. The aims of this study were to investigate the reproductive ecology of the flies and the plant, ascertain the importance of the flies as pollinators and examine the intimate association between flowering events and life history of the flies. We conducted sampling, observations and field pollination experiments. The flies were attracted by the odour of female‐phase inflorescences in the early morning on the first day of anthesis. They fed, mated and oviposited in the inflorescences for 1 day. On the second day, the flies, covered with pollen grains, left the male‐phase inflorescences for the next female‐phase inflorescences. The immature forms of both fly species hatched, developed and pupated within the infructescences without damaging the fruits, and developed adults emerged when the mature infructescences dehisced. The flowering events and fly behaviours were well synchronized. In field pollination experiments, inflorescences bagged with a fine mesh (insect exclusion) produced almost no fruits, whereas those bagged with a coarse mesh (bee exclusion) produced as many fruits as the open‐pollinated controls. These results indicate that these flies are the most efficient and specialised pollinators for their host, A. macrorrhizos. These flies, in return, depend on A. macrorrhizos for food and habitat through most of their life cycle. This study provides a deeper insight into the less recognised, highly intimate pollination mutualism between Araceae plants and Colocasiomyia flies.     

Reproductive trade-offs in a specialized plant/pollinator system involving Asplundia uncinata Harling (Cyclanthaceae) and a derelomine flower weevil (Coleoptera: Curculionidae)

The reproductive interactions of a specialized plant/pollinator system involving Asplundia uncinata Harling (Cyclanthaceae) and a derelomine flower weevil (Coleoptera: Curculionidae: Derelomini) were studied at La Selva, Costa Rica. The inflorescences of A. uncinata exhibit a suite of cantharophilous characters including a precisely synchronized anthesis, protogyny, thermogenesis, olfactory attraction of visitors via modified staminodes, and narrow interfloral entrances. The weevil pollinators use the inflorescences for feeding, mating, and oviposition. The larvae are detritivorous and develop either in the detaching staminate flowers or, at a more favorable rate, in the rotting infructescences. The rate of infructescence abortion was high and caused by low levels of pollination. Manual pollination treatments yielded significantly higher seed counts than obtained under natural conditions, and furthermore demonstrated the inflorescences' ability to reproduce via geitonogamy. In the longer term, the reproductive benefits of maintaining low levels of pollination may shift away from the weevils and towards the plants via an increase in the size of the pollinator population.     

The production of nitric oxide and prostaglandin E(2) by primary bone cells is shear stress dependent

Loading-induced flow of interstitial fluid through the lacuno-canalicular network is a likely signal for bone cell adaptive responses. However, the nature of the stimulus that activates the cell is debated. Candidate stimuli include wall shear stress, streaming potentials, and chemotransport. We have addressed the nature of the flow-derived cell stimulus by comparing variations in fluid transport with variations in wall shear stress, using nitric oxide (NO) and prostaglandin E(2) (PGE(2)) production as a parameter of bone cell activation. Adult mouse long bone cell cultures were treated for 15min with or without pulsating fluid flow using the following regimes: Low PFF, mean flow rate 0.20 cm(3)/s, 3 Hz, shear stress 0.4+/-0.12 Pa; Medium PFF, 0.33 cm(3)/s, 5 Hz, 0.6+/-0.27 Pa; and High PFF, 0.63 cm(3)/s, 9Hz, 1.2+/-0.37 Pa. In some Low PFF experiments, 2.8% neutral dextran (mol. wt. 4.98x10(4)) was added to the flow medium to increase the viscosity, thereby increasing the wall shear stress 3-fold to a level similar of the High PFF stimulus, but without affecting streaming potentials or chemotransport. NO and PGE(2) production were stimulated by Low, Medium, and High PFF in a dose-dependent manner. Application of Low PFF using dextran-supplemented medium, enhanced both the NO and PGE(2) response by 3-fold, to a level mimicking the response to High PFF at normal viscosity. These results show that the production of NO and PGE(2) by bone cells can be enhanced in a dose-dependent manner by fluid flow of increasing wall shear stress. Therefore, the stimulus leading to NO and PGE(2) production is the flow-derived shear stress, and not streaming potentials or chemotransport.     

Biodiversity and ecology of flower-associated actinomycetes in different flowering stages of <Emphasis Type="Italic">Protea repens</Emphasis>

Actinomycete bacteria have previously been reported from reproductive structures (infructescences) of Protea (sugarbush/suikerbos) species, a niche dominated by fungi in the genera Knoxdaviesia and Sporothrix. It is probable that these taxa have symbiotic interactions, but a lack of knowledge regarding their diversity and general ecology precludes their study. We determined the diversity of actinomycetes within Protea repens inflorescence buds, open inflorescences, young and mature infructescences, and leaf litter surrounding these trees. Since the P. repens habitat is fire-prone, we also considered the potential of these bacteria to recolonise infructescences after fire. Actinomycetes were largely absent from flower buds and inflorescences but were consistently present in young and mature infructescences. Two Streptomyces spp. were the most consistent taxa recovered, one of which was also routinely isolated from leaf litter. Lower colonisation rates were evident in samples from a recently burnt site. One of the most consistent taxa isolated from older trees in the unburnt site was absent from this site. Our findings show that P. repens has a distinct community of actinomycetes dominated by a few species. These communities change over time and infructescence developmental stage, season and the age of the host population. Mature infructescences appear to be important sources of inoculum for some of the actinomycetes, seemingly disrupted by fire. Increased fire frequency limiting maturation of P. repens infructescences could thus impact future actinomycete colonisation in the landscape. Streptomyces spp. are likely to share this niche with the ophiostomatoid fungi, which merits further study regarding their interactions and mode of transfer.     

The interplay between inflorescence development and function as the crucible of architectural diversity

Background

Most angiosperms present flowers in inflorescences, which play roles in reproduction, primarily related to pollination, beyond those served by individual flowers alone. An inflorescence''s overall reproductive contribution depends primarily on the three-dimensional arrangement of the floral canopy and its dynamics during its flowering period. These features depend in turn on characteristics of the underlying branching structure (scaffold) that supports and supplies water and nutrients to the floral canopy. This scaffold is produced by developmental algorithms that are genetically specified and hormonally mediated. Thus, the extensive inflorescence diversity evident among angiosperms evolves through changes in the developmental programmes that specify scaffold characteristics, which in turn modify canopy features that promote reproductive performance in a particular pollination and mating environment. Nevertheless, developmental and ecological aspects of inflorescences have typically been studied independently, limiting comprehensive understanding of the relations between inflorescence form, reproductive function, and evolution.

Scope

This review fosters an integrated perspective on inflorescences by summarizing aspects of their development and pollination function that enable and guide inflorescence evolution and diversification.

Conclusions

The architecture of flowering inflorescences comprises three related components: topology (branching patterns, flower number), geometry (phyllotaxis, internode and pedicel lengths, three-dimensional flower arrangement) and phenology (flower opening rate and longevity, dichogamy). Genetic and developmental evidence reveals that these components are largely subject to quantitative control. Consequently, inflorescence evolution proceeds along a multidimensional continuum. Nevertheless, some combinations of topology, geometry and phenology are represented more commonly than others, because they serve reproductive function particularly effectively. For wind-pollinated species, these combinations often represent compromise solutions to the conflicting physical influences on pollen removal, transport and deposition. For animal-pollinated species, dominant selective influences include the conflicting benefits of large displays for attracting pollinators and of small displays for limiting among-flower self-pollination. The variety of architectural components that comprise inflorescences enable diverse resolutions of these conflicts.     

Relationship between floral longevity and sex allocation among flowers within inflorescences in Aquilegia buergeriana var. oxysepala (Ranunculaceae)

Understanding the fitness of plants with inflorescences requires examining variation in sex allocation among flowers within inflorescences. We examined whether differences in the duration of the male and female phases of flowering lead to variation in sex allocation and reproductive success among flowers within inflorescences. In 2002 and 2003, we quantified floral longevity, floral sex allocation, and reproductive success between the first and the second flowers within inflorescences in a protandrous species, Aquilegia buergeriana var. oxysepala. Floral longevity was greater in the first flowers than in the second ones in both years. The male phase lasted longer, and the initial number of pollen grains and the number of pollen grains removed were greater in the first flowers than in the second ones in both years. Within first flowers, the number of pollen grains removed was greater in flowers that had longer male phases, thus duration of the male phase may positively affect male reproductive success in the first flowers. The female phase lasted longer and the number of ovules was greater in the first flowers than in the second only in 2002. However, seed production per flower and female phase duration in both years were not significantly related. The variation in the number of pollen grains among flowers in this species may be caused by the variation in male phase duration.     

Structural deformation of bacterial biofilms caused by short-term fluctuations in fluid shear: an in situ investigation of biofilm rheology.

The physical properties (rheology) of biofilms will determine the shape and mechanical stability of the biofilm structure and consequently affect both mass transfer and detachment processes. Biofilm viscoelasticity is also thought to increase fluid energy losses in pipelines. Yet there is very little information on the rheology of intact biofilms. This is due in part to the difficulty in using conventional testing techniques. The size and nature of biofilms makes them difficult to handle, while removal from a surface destroys the integrity of the sample. We have developed a method which allowed us to conduct simple stress-strain and creep experiments on mixed and pure culture biofilms in situ by observing the structural deformations caused by changes in hydrodynamic shear stress (tau(w)). The biofilms were grown under turbulent pipe flow (flow velocity (u) = 1 m/s, Reynolds number (Re) = 3600, tau(w) = 5. 09 N/m(2)) for between 12 and 23 days. The resulting biofilms were heterogeneous and consisted of filamentous streamers that were readily deformed by changes in tau(w). At tau(w) of 10.11 N/m(2) the streamers were flattened so that the thickness was reduced by 25%. We estimated that the shear modulus (G) of the mixed culture biofilm was 27 N/m(2) and the apparent elastic modulus (E(app)) of both biofilms was in the range of 17 to 40 N/m(2). The biofilms behaved like elastic and viscoelastic solids below the tau(w) at which they were grown but behaved like viscoelastic fluids at elevated tau(w). The implications of these results for fluid energy losses and the processes of mass transfer and detachment are discussed.     

Pollination and reproductive success of two colour variants of a deceptive orchid, Dactylorhiza maculata (Orchidaceae)

Polymorphism in petal colour is common in deceptively pollinated plant species. Most of the deceptively pollinated orchids are food frauds, and in most of them, the deception is not mimetic. These plants have conspicuously coloured flowers which they use as the main attractant of naive pollinators. In a field experiment, we studied the response of bumblebees and other types of flower visitors to colour differences between experimentally paired plants of Dactylorhiza maculata , a nectarless food-deceptive species. In addition, pollen removal, an estimate of male fitness, and fruit production, an estimate of female fitness, were measured in the two colour variants. We found a trend of bumblebee preference for the dark-coloured flowers, but other flower visitors (as a group) showed no preference for any colour variant. No difference was found in the reproductive success between the two colour variants of D. maculata. The lack of a difference in reproductive success between plants with pale and dark inflorescences, despite the observed trend of bumblebee preference for dark inflorescences, suggests that there is some balancing factor in the pollination of the pale inflorescences. An excess of visits by some nocturnal species (or a group of species) which favours the pale colour of D. maculata inflorescences or an excess of visits during day time by some flower visitors other than bumblebees preferring the pale inflorescences over dark ones may form such a balancing factor.     

Apios americana,a fly-pollinated papilionaceous flower?

In the flowers ofApios americana the vexillum remains ± in its bud position. In this way, a dark cavity is formed displaying a bright window at its base. Insect visitors are attracted to the hidden inflorescences by scent. In their attempt to reach the window they trigger an explosive release of stigma and pollen. Stigmatic fluid glues pollen to the visitor. All characters of the flower fit well into the myiophilous syndrome and thus flies are expected to be the proper pollinators.Apios americana seems to be the only myiophilous exception within the predominantly melittophilousFabaceae.     

A covalently cross-linked gel derived from the epidermis of the pilot whale Globicephala melas

The rheological properties of the stratum corneum of the pilot whale (Globicephala melas) were investigated with emphasis on their significance to the self-cleaning abilities of the skin surface smoothed by a jelly material enriched with various hydrolytic enzymes. The gel formation of the collected fluid was monitored by applying periodic-harmonic oscillating loads using a stress-controlled rheometer. In the mechanical spectrum of the gel, the plateau region of the storage modulus G' (<1200 Pa) and the loss modulus G" (>120 Pa) were independent of frequency (omega = 43.98 to 0.13 rad x s(-1), tau = 15 Pa, T = 20 degrees C), indicating high elastic performance of a covalently cross-linked viscoelastic solid. In addition, multi-angle laser light scattering experiments (MALLS) were performed to analyse the potential time-dependent changes in the weight-average molar mass of the samples. The observed increase showed that the gel formation is based on the assembly of covalently cross-linked aggregates. The viscoelastic properties and the shear resistance of the gel assure that the enzyme-containing jelly material smoothing the skin surface is not removed from the stratum corneum by shear regimes during dolphin jumping. The even skin surface is considered to be most important for the self-cleaning abilities of the dolphin skin against biofouling.     

Pollination mutualism between a new species of the genus Colocasiomyia de Meijere (Diptera: Drosophilidae) and Steudnera colocasiifolia (Araceae) in Yunnan, China

A new species of the genus Colocasiomyia de Meijere (Diptera: Drosophilidae) was discovered from inflorescences of Steudnera colocasiifolia K. Koch (Araceae) in Yunnan, China. The new species is described as Colocasiomyia steudnerae Takenaka and Toda, sp. nov., and we investigated the reproductive ecology of both the fly and the plant species. This fly species reproduces in the inflorescences/infructescences of the plant, and depends almost throughout its entire life cycle on the host plant. The fly species is the most abundant flower visitor for S. colocasiifolia and behaves intimately with the flowering events, suggesting that it is the unique and most efficient pollinator for the host plant. Bagging (insect‐exclusion) treatment of inflorescences resulted in no fruits. These findings strongly suggest that intimate pollination mutualism has evolved between the fly and the host plant, as are known in other Colocasiomyia flies and Araceae plants. One notable feature of this system is that the new species almost monopolizes the host‐plant inflorescence as a visitor, without any cohabiting Colocasiomyia species. In comparison to other cases where two Colocasiomyia species share the same inflorescence and infructescence of Araceae host plants for reproduction by separating their breeding niches microallopatrically between the staminate (upper male‐flower) and the pistillate (lower female‐flower) regions on the spadix, C. steudnerae exhibits a mixture of stamenicolous and pistillicolous breeding habits.     

AEROBIOLOGY AND POLLEN CAPTURE OF ORCHARD-GROWN PISTACIA VERA (ANACARDIACEAE)

The phenology of pollen release and pollen capture by Pistacia vera was studied in the field and laboratory respectively. Inflorescences of Pistacia vera were examined in a wind tunnel to determine whether the behavior of airborne conspecific pollen around receptive flowers differed as a result of changes in the shape and size of the inflorescence. In addition, the behavior of unclumped (single) and clumped pollen grains was studied to determine differences in the probability of their capture. Wind speeds within a commercial orchard during pollen shedding averaged 0.9–2.2 m/sec and atmospheric pollen concentrations were highest between 0900–1100 hr MST. Each of three stages in inflorescence development (defined on the basis of the number of exserted stigmas) was examined under identical ambient airflow conditions with equal concentrations of airborne pollen (1,000 grains/m³). The general pattern of pollen grain motion involves direct inertial collision by windward surfaces and by sedimentation of pollen onto leeward surfaces; clumped pollen rarely sedimented onto leeward surfaces. Small changes in ambient wind speed (0.5 m/sec to 1.0 m/sec) produced significant changes in the pattern of pollen motion around inflorescences and altered the number of pollen grains captured by leeward surfaces. Thus, wind pollination in P. vera is affected both by windspeed and by the shape or size of flower clusters. Differences in the behavior of clumped and unclumped pollen result from their inertial properties and responsiveness to local changes in the direction and speed of airflow. Unclumped pollen has a higher probability of being captured by leeward surfaces. The apparent insensitivity of pollen motion to differences in inflorescence size may ensure equitable pollination during the acropetal development of flowers.