Raising the Sugar Content – Orchid Bees Overcome the Constraints of Suction Feeding through Manipulation of Nectar and Pollen Provisions

Unlike most other bees, the long-tongued orchid bees ingest nectar using suction feeding. Although long tongues allow exploitation of flowers with deep spurs, the energy intake rate is optimal at 10–20% lower nectar sugar concentrations compared to that of lapping bees. This constraint might be compensated by a higher digestive throughput. Additionally, orchid bees might evaporate water from regurgitated droplets of crop contents. We found male Euglossa championi (n = 10) and Euglossa dodsoni (n = 12) to regularly regurgitate droplets of crop content to the base of their proboscis, generating a fluid film between the proximal parts of the galeae, glossa and labial palps. Rhythmic movements of the proboscis may help to increase convection. There was a significant change in sugar concentration between the initially imbibed solution and the resulting crop content (P<0.05) and the time individual bees had engaged in this liquid exposure behavior was positively correlated with the resulting crop sugar concentration. Female Euglossa townsendi and Euglossa viridissima showed the same behavior. Additionally, they manipulated their nectar-enriched pollen provisions for extensive periods of time before deposition in brood cells. The deposited pollen loads (n = 14) showed a significantly higher sugar concentration than the sugar-water available to the bees (P<0.001). Thus, both male and female euglossines show behaviors that promote evaporative water loss from nectar. We suggest that the behaviors have evolved in concert with suction feeding on dilute nectar from deep floral tubes.     

Heat sensitivity of photosynthetic electron transport varies during the day due to changes in sugars and osmotic potential

In water-stressed leaves, accumulation of neutral osmotica enhances the heat tolerance of photosynthetic electron transport. There are large diurnal and day-to-day changes in leaf sugar content because of variations in net photosynthetic production, respiration and retranslocation. To test the hypothesis that diurnal and day-to-day variations in leaf sugar content and osmotic potential significantly modify the responses to temperature of photosynthetic electron transport rate, we studied chlorophyll fluorescence rise temperatures (i.e. critical temperatures at break-points in fluorescence versus temperature response curves, corresponding to enhanced damage of PSII centers and detachment of pigment-binding complexes) in the dark at a background of weak far-red light (T(FR)) and under actinic light (T(L)), and responses of foliar photosynthetic electron transport rate to temperature using gas-exchange and chlorophyll fluorescence techniques in the temperate tree Populus tremula L. Sucrose and sorbitol feeding experiments demonstrated strong increases of fluorescence rise temperatures T(FR) and T(L) with decreasing leaf osmotic potential and increasing internal sugar concentration. Similar T(FR) and T(L) changes were observed in response to natural variation in leaf sugar concentration throughout the day. Increases in leaf sugar concentration led to an overall down-regulation of the rate of photosynthetic electron transport (J), but increases in the optimum temperature (Topt) of J. For the entire dataset, Topt varied from 33.8 degrees C to 43 degrees C due to natural variation in sugars and from 33.8 degrees C to 52.6 degrees C in the sugar feeding experiments, underscoring the importance of sugars in modifying the response of J to temperature. However, the correlations between the sugar concentration and fluorescence rise temperature varied between the days. This variation in fluorescence rise temperature was best explained by the average temperature of the preceding 5 or 6 days. In addition, there was a significant year-to-year variation in heat sensitivity of photosynthetic electron transport that was associated with year-to-year differences in endogenous sugar content. Our data demonstrate a diurnal variation in leaf heat tolerance due to changes in sugar concentration, but they also show that this short-term modification in heat tolerance is super-imposed by long-term changes in heat resistance driven by average temperature of preceding days.     

Feeding of the megamouth shark (Pisces: Lamniformes: Megachasmidae) predicted by its hyoid arch: A biomechanical approach

Studies of the megamouth shark, one of three planktivorous sharks, can provide information about their evolutionary history. Megamouth shark feeding has never been observed in life animals, but two alternative hypotheses on biomechanics suggest either feeding, i.e., ram feeding or suction feeding. In this study, the second moment of area of the ceratohyal cartilages, which is an indicator of the flexural stiffness of the cartilages, is calculated for 21 species of ram‐ and suction‐feeding sharks using computed tomography. The results indicate that suction‐feeding sharks have ceratohyal cartilages with a larger second moment of area than ram‐feeding sharks. The result also indicates that the ram–suction index, which is an indicator of relative contribution of ram and suction behavior, is also correlated with the second moment of area of the ceratohyal. Considering that large bending stresses are expected to be applied to the ceratohyal cartilage during suction, the larger second moment of area of the ceratohyal of suction‐feeding sharks can be interpreted as an adaptation for suction feeding. Based on the small second moment of area of the ceratohyal cartilage of the megamouth shark, the feeding mode of the megamouth shark is considered to be ram feeding, similar to the planktivorous basking shark. From these results, an evolutionary scenario of feeding mechanics of three species of planktivorous sharks can be suggested. In this scenario, the planktivorous whale shark evolved ram feeding from a benthic suction‐feeding ancestor. Ram feeding in the planktivorous megamouth shark and the basking shark evolved from ram feeding swimming‐type ancestors and that both developed their unique filtering system to capture small‐sized prey. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Salt processing in larval Drosophila: choice, feeding, and learning shift from appetitive to aversive in a concentration-dependent way

Sodium and chloride need to be ingested and cannot be stored. Therefore, choice of habitat and diet as related to NaCl needs to be tightly regulated. We thus expect that the behavioral effects of salt are organized according to its concentration. Here, we comparatively "fingerprint" the reflex releasing (in choice and feeding experiments) versus the reinforcing effects of sodium chloride ("salt") in terms of their concentration dependencies, using larval Drosophila. Qualitatively, we find that the behavioral effects of salt in all 3 assays are similar: choice, feeding, and reinforcing effect all change from appetitive to aversive as concentration is increased. Quantitatively, however, the appetitive effects for choice and feeding share their optimum at around 0.02 M, whereas the dose-response curve for the reinforcing effect is shifted by more than one order of magnitude toward higher concentrations. Interestingly, a similar shift between these 2 kinds of behavioral effect is also found for sugars (Schipanski et al. 2008). Thus, for salt and for sugar, the sensory-to-motor system is more sensitive regarding immediate, reflexive behavior than regarding reinforcement. We speculate that this may partially be due to a dissociation of the sensory pathways signaling toward either reflexive behavior or internal reinforcement.     

The control of the proventriculus in the honeybee (Apis mellifera carnica L.) I. A dynamic process influenced by food quality and quantity?

The control of crop emptying in foraging honeybees was investigated in individuals trained to collect defined amounts of sugar solutions. Following feeding, they were dissected after fixed periods of time in order to measure crop content and haemolymph sugar titers. Between feeding and dissection, the metabolic rate of every investigated forager was measured using open-flow respirometry, so as to assess the effects of both food quality (concentration, molarity and viscosity of the fed sugar solution) and food quantity on the transport rate through the proventriculus. The sugar transport rate through the proventriculus was observed to be mainly dependent on the metabolic expenditure of the individual. Bee foragers were able to precisely adjust the sugar transport rate to their metabolic rates, but under certain conditions, an excess of sugars was transported through the proventriculus, more than needed to cover the bee’s energetic demands. This excess depended on the nutritive value and quantity of the fed sugar solution, and on the time after feeding. It did not depend on the metabolic rate of the bee, the molarity, or the viscosity of the fed sugar solution. As long as the bees did not exhaust their crop contents, the haemolymph sugar titers were unaffected by this excess amount transported, by the time after feeding, the concentration and the viscosity of the fed sugar solution. For all feeding conditions assayed, the haemolymph trehalose titer remained constant, while the titers of other haemolymph sugars varied. It is suggested that the trehalose concentration in the haemolymph is regulated in honeybees, and that it represents the controlled variable in the feedback loop responsible for the transport rate through the proventriculus.     

Chromosaponin I stimulates the sugar taste receptor cells of the blowfly, Phormia regina

Chromosaponin I (CSI), a gamma-pyronyl-triterpenoid saponin isolated from pea and other leguminous plants, stimulates the growth of roots in a variety of plants. In the present work, we introduce CSI as a sugar taste substance for the blowfly, Phormia regina. The blowfly has taste chemosensilla on the labellum. The sensory receptor cells in the chemosensillum are highly specialized for the tastes of sugar, salt and water, respectively. Application of CSI induced the feeding response of blowflies including full proboscis extension. CSI also induced impulses of the sugar taste receptor cell in the LL-type sensillum. The optimum concentration of CSI in these responses was 0.1 mM which is much lower than that of sucrose. Based on the comparison of dose-response relationships, CSI is 100 times more effective than sucrose in stimulating the sugar taste receptor cells. CSI-induced impulses appeared after a significant latency compared with sucrose. As far as we know, this is the first report describing that a natural saponin induces sugar responses in insects. CSI is a unique saponin because of its bifunctional property in plants and insects.     

On the mechanics and energetics of nectar feeding in butterflies.

A mechanistic model describing the mechanics and energetics of nectar-feeding in butterflies is developed. The butterflies Collas eurytheme and Danaus plexippus are used to illustrate the model. Simulation results indicate that there are mechanical limitations upon the range of nectar sugar concentrations and nectar extraction times available to butterflies. There is a unique optimum for net rate of energy gain at 20–25% nectar sugar concentration which is independent of the metabolic rate and of proboscis shape and size over the ranges found in butterflies. The optimal nectar extraction rate depends upon the size and shape of the proboscis. These results are discussed in relation to the design of nectar feeding structures, optimal foraging strategy, and the evolution of insect pollination.     

Effects of feeding frequency and sugar concentrations on lifetime reproductive success of Meteorus pulchricornis (Hymenoptera: Braconidae)

Many species of parasitoids can increase their reproduction through feeding on supplemental sugar sources. We evaluated the longevity both with and without hosts and progeny production of a uniparental strain of Meteorus pulchricornis by varying concentration of the sugar solution and feeding frequency. A 1:1:1 sucrose–glucose–fructose-mixture was tested in a range of concentrations (0–70% (w/v)). The parasitoid lifespan did not increase with the concentration of sugar solutions, but parasitoids feeding on a 30% sugar solution attained greater longevity than parasitoids feeding on other sugar concentrations in the absence of hosts. The same effect of sugar concentration was also observed on progeny production, where when the parasitoid was fed 30% (w/v) sugar solution, its lifetime progeny production doubled in comparison to that fed water, and increased by 50% compared to those fed the other sugar solutions. In the last experiment, we studied the effect of feeding intervals on the longevity and progeny production of M. pulchricornis. Parasitoids fed with a 30% (w/v) 1:1:1 sucrose–glucose–fructose-mixture continuously lived six times longer than unfed parasitoids, three times longer than parasitoids fed only once and two times longer than parasitoids fed once every two days in the absence of hosts. Parasitoids with continuous access to the sugar solution produced considerably more progeny than those with fewer feeding frequencies. This increasing progeny production was accomplished more through an increase in daily offspring production rather than through extending reproductive lifespan.     

Comparative anatomy and evolutionary history of suction feeding in cetaceans

Some odontocetes possess unique features of the hyolingual apparatus that are involved in suction feeding. The hyoid bone and associated musculature generates rapid, piston‐like retraction, and depression of the hyoid and tongue. “Capture” suction feeders (e.g., Globicephala) use suction for capturing and swallowing prey. “Combination” feeders (i.e., Lagenorhynchus) use both raptorial feeding (to capture prey) and suction (to ingest prey). In “capture” suction feeders, features of the hyoid and skull have been attributed to creating suction (i.e., large surface area and mandibular bluntness). In addition to odontocetes, a mysticete, the gray whale (Eschrichtius robustus), is considered a benthic suction feeder. However, anatomical studies of purported suction‐feeding structures of the gray whale are lacking. In addition, few studies have utilized evolutionary approaches to understand the history of suction feeding in cetaceans. This study incorporates quantitative and qualitative hyoid and cranial data from 35 extant and 14 extinct cetacean species into a multivariate principal component analysis and comparative phylogenetic analyses. Conclusions from these analyses are that some commonly attributed features (i.e., ventral throat grooves and mandibular bluntness) and one principal component are significantly correlated with suction feeding. Finally, ancestral state reconstructions indicate that suction feeding likely evolved once, early in cetacean evolutionary history.     

Foraging behavior adjustments related to changes in nectar sugar concentration in phyllostomid bats

Nectar-feeding bats regulate their food ingestion in response to changes in sugar concentration as a way to achieve a constant energy intake. However, their digestive capability to assimilate sugars can limit their total energy intake, particularly when sugar concentration in nectar is low. Our experimental study evaluated the effect that changes in sugar concentration of nectar have on the foraging behavior of the nectar-feeding bats Glossophaga soricina and Leptonycteris yerbabuenae in captivity. We measured foraging behavior and food intake when bats fed at different concentrations of sucrose (5, 15, 25 and 35%wt/vol.). To compensate for low-energy intake, both bat species reduced their flight time, and increased feeding time when sugar concentration decreased. Our results suggest that nectar-feeding bats in nature confront two scenarios with complementary ecological effects: 1) bats feeding on dilute nectars (i.e. ≤15%wt/vol.) should increase the number of flowers visited per night enhancing pollination, and 2) bats feeding on concentrated nectars could spend more time flying, including long- and short-distance-flights increasing food patch exploration for use during subsequent nights, and thus enhancing plant gene flow. Further studies on foraging behavior of nectarivorous bats under natural conditions are necessary to corroborate these hypotheses.     

Nectar intake of white-bellied sunbirds (Cinnyris talatala): can meal size be inferred from feeding duration?

A positive relationship between feeding duration and meal size of avian nectarivores has often been assumed in earlier studies. We investigated whether feeding duration can be used as a surrogate for the amount of sugar solution ingested by white-bellied sunbirds, Cinnyris (Nectarinia) talatala. Feeding durations of sunbirds consuming three sucrose concentrations (10%, 20%, and 40% w/w) were measured using an infrared photodetection system, and the amounts consumed were recorded simultaneously by weighing the feeder throughout the experiment. For all three diet concentrations, a positive relationship was found between the time spent feeding per 30 min and the mass consumed. Therefore, feeding duration is demonstrated to be an index of the amount ingested on a particular sugar concentration. The rate of ingestion, however, depended on the sugar concentration, with the highest rate at the lowest concentration of 10% and the lowest rate at the 40% concentration. Less total time was spent feeding on the 20% solution than on the 10% solution, but time increased on the 40% diet because of viscosity effects. There appeared to be a weak relationship between feeding patterns and sex, but this was not significant, probably because of interindividual variation.     

发酵工艺条件的多目标优化

以模糊综合评价值作为评价指标、加权单纯形方法优化发酵过程工艺条件。应用本方法,对以谷氨酸发酵废液为原料的酵母发酵过程的发酵温度、ｐＨ、菌种量、初始糖浓度、通气量及流加液糖浓度等工艺条件进行了优化。     

Feeding and survival in parasitic wasps: sugar concentration and timing matter

Sugar consumption can increase the longevity and lifetime fecundity of many species of parasitic wasps. Consequently, for these insects the availability of sugar sources in the field is important for their reproductive success. As sugar sources can be highly variable in quantity, space and time, the chances of finding a sufficient amount of sugar to increase longevity might be very low. Therefore, the reward from a single feeding event can be critical for the forager's fitness. We measured the longevity of the parasitoid Cotesia rubecula after a single honey meal differing in sugar concentration (25, 47, 86% w/w) and timing (day of emergence and 24 h later). Survival was analysed with Cox's Proportional Hazards Model. The risk of starving to death in sugar-fed wasps was reduced by 0–73% in comparison to unfed wasps, depending on sugar concentration and timing. Longevity was significantly increased by sugar concentration and by feeding later in life. Our results suggest that in the field, adult C. rubecula has to locate food at least once per day to avoid starvation.     

Changes in food source profitability affect Nasonov gland exposure in honeybee foragers Apis mellifera L.

Summary. When arriving at a known artificial food source, foraging honeybees usually perform circular flights around the feeding place prior to landing. During these flights bees expose their Nasonov gland, an exocrine gland located at the base of the 7^th tergum, that releases a complex blend of volatiles. This behavior may continue even after the bee starts food ingestion. The proportion of bees exposing the Nasonov gland and the duration of its exposure before and during feeding for individual bees were quantified. Trained bees collected sugar solution during 12 visits from a feeder located at 160 m from the hive. Five different reward programs were presented: three constant and two variable. The constant programs offered 0.6, 1.2 or 2.4 M sugar for all 12 visits, while the variable programs delivered either 0.6, 1.2, 0.6 M or 0.6, 2.4, 0.6 M, four visits for each molarity. Results showed that sugar concentration changed the thresholds and durations of Nasonov gland exposure. However, this relationship was found only for Nasonov exposure before bees began to feed. During feeding, a protruded Nasonov gland was only observed for bees that had exposed it prior to feeding; suggesting that Nasonov gland exposure before feeding is a releaser of the during-feeding exposure. In variable reward programs, changes in sugar concentration were followed by changes in both thresholds and durations of exposure. However, Nasonov gland exposure during feeding did not appear to decrease based on measurements of the low profitability during the current foraging visit. These results suggest that Nasonov gland exposure is programmed on the basis of reward expectations, with the bees having acquired this information in the previous foraging visits to the food source.     

Effects of snout dimensions on the hydrodynamics of suction feeding in juvenile and adult seahorses

Seahorses give birth to juveniles having a fully functional feeding apparatus, and juvenile feeding behaviour shows striking similarities to that of adults. However, a significant allometric growth of the snout is observed during which the snout shape changes from relatively short and broad in juveniles to relatively long and slender in adults. Since the shape of the buccal cavity is a critical determinant of the suction performance, this snout allometry will inevitably affect the suction feeding ability. To test whether the snout is optimised for suction feeding throughout an ontogeny, we simulated the expansion of different snout shapes varying from extremely long and slender to short and broad for juvenile and adult snout sizes, using computational fluid dynamic models. Our results showed that the snout diameter at the start of the simulations is involved in a trade-off between the realizable suction volume and expansion time on the one hand (improving with larger initial diameters), and maximal flow velocity on the other hand (improving with smaller initial diameters). Moreover suction performance (suction volume as well as maximal attainable flow velocity) increased with decreasing snout length. However, an increase in snout length decreases the time to reach the prey by the cranial rotation, which may explain the prevalence of long snouts among syngnathid fishes despite the reduced suction performance. Thus, the design of the seahorse snout revolves around a trade-off between the ability to generate high-volume suction versus minimisation of the time needed to reach the prey by the cranial rotation.     

Suction feeding mechanics, performance, and diversity in fishes

Despite almost 50 years of research on the functional morphologyand biomechanics of suction feeding, no consensus has emergedon how to characterize suction-feeding performance, or its morphologicalbasis. We argue that this lack of unity in the literature isdue to an unusually indirect and complex linkage between themuscle contractions that power suction feeding, the skeletalmovements that underlie buccal expansion, the sharp drop inbuccal suction pressure that occurs during expansion, the flowof water that enters the mouth to eliminate the pressure gradient,and the forces that are ultimately exerted on the prey by thisflow. This complexity has led various researchers to focus individuallyon suction pressure, flow velocity, or the distance the preymoves as metrics of suction-feeding performance. We attemptto integrate a mechanistic view of the ability of fish to performthese components of suction feeding. We first discuss a modelthat successfully relates aspects of cranial morphology to thecapacity to generate suction pressure in the buccal cavity.This model is a particularly valuable tool for studying theevolution of the feeding mechanism. Second, we illustrate themultidimensional nature of suction-feeding performance in acomparison of bluegill, Lepomis macrochirus, and largemouthbass, Micropterus salmoides, two species that represent oppositeends of the spectrum of performance in suction feeding. As anticipated,bluegills had greater accuracy, lower peak flux into the mouth,and higher flow velocity and acceleration of flow than did bass.While the differences between species in accuracy of strikeand peak water flux were substantial, peak suction velocityand acceleration were only about 50% higher in bluegill, a relativelymodest difference. However, a hydrodynamic model of the forcesthat suction feeders exert on their prey shows that this differencein velocity is amplified by a positive effect of the smallermouth aperture of bluegill on force exerted on the prey. Ourmodel indicates that the pressure gradient in front of a fishthat is feeding by suction, associated with the gradient inwater velocity, results in a force on the prey that is largerthan drag or acceleration reaction. A smaller mouth apertureresults in a steeper pressure gradient that exerts a greaterforce on the prey, even when other features of the suction floware held constant. Our work shows that some aspects of suction-feedingperformance can be determined from morphology, but that thecomplexity of the behavior requires a diversity of perspectivesto be used in order to adequately characterize performance.     

Ethanol production from sweet sorghum juice in batch and fed-batch fermentations by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Sweet sorghum juice supplemented with 0.5% ammonium sulphate was used as a substrate for ethanol production by Saccharomyces cerevisiae TISTR 5048. In batch fermentation, kinetic parameters for ethanol production depended on initial cell and sugar concentrations. The optimum initial cell and sugar concentrations in the batch fermentation were 1 × 10⁸ cells ml⁻¹ and 24 °Bx respectively. At these conditions, ethanol concentration produced (P), yield (Y _ps) and productivity (Q _p ) were 100 g l⁻¹, 0.42 g g⁻¹ and 1.67 g l⁻¹ h⁻¹ respectively. In fed-batch fermentation, the optimum substrate feeding strategy for ethanol production at the initial sugar concentration of 24 °Bx was one-time substrate feeding, where P, Y _ps and Q _p were 120 g l⁻¹, 0.48 g g⁻¹ and 1.11 g l⁻¹ h⁻¹ respectively. These findings suggest that fed-batch fermentation improves the efficiency of ethanol production in terms of ethanol concentration and product yield.     

Effect of sugar-feeding strategies on astaxanthin production by <Emphasis Type="Italic">Xanthophyllomyces dendrorhous</Emphasis>

Summary Astaxanthin, a main carotenoid pigment, has a strong antioxidant activity. The effects of sugar-feeding strategies on astaxanthin production by Xanthophyllomyces dendrorhous fed-batch fermentation were studied. Sugar was added instantaneously to a 30 l fermentor at various discrete time instants (pulse-feeding), or continuously to the fermentor to maintain the constant sugar concentration. Pulse-feeding experiments were initiated with sugar concentrations from 30 to 50 g/l, and then one, two, three and four feedings were made. The results showed that optimal sugar feeding depended on feeding time and pulse sugar feeding was the best among all experiments, in which a significant increase (54.9%) in production of astaxanthin was achieved at 132 h in a pulse fed-batch process compared with a batch process.     

Is nasogastric suction necessary in acute pancreatitis?

Fifty-eight patients with mild to moderately severe acute pancreatitis were randomly allocated to treatment with or without nasogastric suction (27 and 31 patients respectively). Intravenous fluids and pethidine hydrochloride were also given. The two groups were comparable clinically at the start of the study. There were no differences between the two groups in the mean duration of the following features: abdominal pain or tenderness; absence of bowel movements; raised serum amylase concentration; time to resumption of oral feeding; and days in hospital. Prolonged hyperamylasaemia (serum amylase greater than 0.33 mU/l) occurred in one patient in the suction group and in three patients in the non-suction group. A mild recurrence of abdominal pain after resumption of oral feeding occurred in three patients in the suction group and in two patients in the non-suction group. Two patients in the suction group developed overt consumption coagulopathy and two others pulmonary complications. No patient in the non-suction group had complications. The findings suggest that most patients with mild to moderately severe acute pancreatitis do not benefit from nasogastric suction. The procedure should be elective rather than mandatory in treating this condition.     

Cranial movements during suction feeding in teleost fishes: Are they modified to enhance suction production?

Suction is produced during prey capture by most teleost fishes. Here, we ask two questions about the functional basis of suction feeding. First, is there variation in the kinematic pattern produced by different species while suction feeding? Second, do species termed 'suction specialists' demonstrate similar modifications to their feeding behavior? We used 10 kinematic variables in a principal component analysis to identify axes of variation among 14 suction feeding teleost species (representing nine families and five orders within the Euteleostei) that demonstrate different feeding habits and habitats. MANOVA and Tukey post hoc tests were used to assess differences among species. Most species clustered together on the principal component axes, suggesting a generalized mechanism that facilitates unidirectional flow. Typically, only one species stood out as 'extreme' on each functional axis, and a species that stood out on one axis did not stand out on others. Only one species, the flatfish Pleuronichthys verticalis, an obligate benthic feeder, demonstrated modifications consistent with enhanced suction production. This species displayed a suite of changes that should enhance suction production, including large hyoid depression, large cranial rotation, and small gape. We suggest that suction performance may be greatest in such obligate benthic feeders because cranial morphology is highly modified and prey are captured from the substrate.