Nitrogen-stable isotopic signatures of basal food items, primary consumers and omnivores in rivers with different levels of human impact

We examined how nitrogen-stable isotopic signatures of food web components (basal resources, primary and lower consumers, and omnivores) in rivers change with increasing levels of human population density (HPD) in their watersheds. Samples were collected from 22 rivers flowing in the Lake Biwa basin, Japan. Among three potential resources at the base of food webs (epilithon, benthic and suspended particulate organic matter), the mean isotopic values (δ¹⁵N) of the epilithon (4.5–7.8%) were consistently higher than those of other items (1.9–4.2%) and displayed the most pronounced elevation (by 3.3%) with increasing HPD. The mean δ¹⁵N values of the individual taxa of lower consumers (bivalve, snail and caddisfly) tended to increase with increasing HPD, although the pattern and the extent of the elevation were highly variable among the taxa. These results suggest a taxon-specific feature in the N source (or sources) of lower consumers. Our data suggested that human activities (e.g. nutrient loading) potentially induce changes in the N baselines of river food webs. The major N source of bivalves appeared to be shifted from suspended particulate organic matter to other items with increasing HPD. Trophic levels of goby fish (Rhinogobius sp. OR) and shrimp (Palaemon paucidens), being estimated to be at 2.4–3.8 and 2.1–3.4, respectively, did not differ significantly among rivers with different HPD levels. An erratum to this article can be found at     

Energy flow to two abundant consumers in a subtropical oyster reef food web

Oyster reefs are among the most threatened coastal habitat types, but still provide critical habitat and food resources for many estuarine species. The structure of oyster reef food webs is an important framework from which to examine the role of these reefs in supporting high densities of associated fishes. We identified major trophic pathways to two abundant consumers, gray snapper (Lutjanus griseus) and crested goby (Lophogobius cyprinoides), from a subtropical oyster reef using stomach content and stable isotope analysis. The diet of gray snapper was dominated by crabs, with shrimp and fishes also important. Juvenile gray snapper fed almost entirely on oyster reef-associated prey items, while subadults fed on both oyster reef- and mangrove-associated prey. Based on trophic guilds of the gray snapper prey, as well as relative δ¹³C values, microphytobenthos is the most likely basal resource pool supporting gray snapper production on oyster reefs. Crested goby had omnivorous diets dominated by bivalves, small crabs, detritus, and algae, and thus were able to take advantage of prey relying on production from sestonic, as well as microphytobenthos, source pools. In this way, crested goby represent a critical link of sestonic production to higher trophic levels. These results highlight major trophic pathways supporting secondary production in oyster reef habitat, thereby elucidating the feeding relationships that render oyster reef critical habitat for many ecologically and economically important fish species.     

Translating available food into the number of eggs laid by Drosophila melanogaster

In Drosophila and other insects egg production is related to the nutrients available. Somehow the nutritional status of the environment is translated into hormonal signs that can be "read" by each individual egg chamber, influencing the decision to either develop into an egg or die. We have shown that BR-C is a control gene during oogenesis and that the differential expression of BR-C isoforms plays a key role in controlling whether the fate of the egg chamber is to develop or undergo apoptosis.     

Feeding hermit crabs to shrimp broodstock increases their risk of WSSV infection

White spot syndrome virus (WSSV) is a serious shrimp pathogen that has spread globally to all major shrimp farming areas, causing enormous economic losses. Here we investigate the role of hermit crabs in transmitting WSSV to Penaeus monodon brooders used in hatcheries in Vietnam. WSSV-free brooders became PCR-positive for WSSV within 2 to 14 d, and the source of infection was traced to hermit crabs being used as live feed. Challenging hermit crabs with WSSV confirmed their susceptibility to infection, but they remained tolerant to disease even at virus loads equivalent to those causing acute disease in shrimp. As PCR screening also suggests that WSSV infection occurs commonly in hermit crab populations in both Vietnam and Taiwan, their use as live feed for shrimp brooders is not recommended.     

The fruits available as food to small rodents in two woodland ecosystems

The fruit fall from the canopy and the understorey in an oak Quercus petraea (Mattushka) Liebl. wood and in a yew Taxus baccata L. wood at Killarney, Ireland, were measured over a period of approximately 13 months; this included two complete fruit crops in each wood. Fruit represents the great bulk of the food of the small rodents present: wood mice Apodemus sylvaticus (L.) and bank voles Clethrionomys glareolus Schreber. From a knowledge of the particular fruits or their parts eaten, the amounts of available food, in kcal ha^-1 were derived. In each ecosystem the food potentially available to small rodents in one crop was five times that in the other.     

Modelling interactions of food quality and quantity in homeostatic consumers

1. Boundaries between growth limitation by carbon (C) and phosphorus (P) in homeostatic heterotrophic consumers such as zooplankton will vary as demands on these two elements vary, as they should at different food quantities. At very low food quantity when production is close to zero, metabolic requirements (for carbon) become more important than growth requirements (for carbon and phosphorus in fixed proportion). Thus, the boundary separating C-and P-limited growth should be at a higher C : P ratio at low food quantity than at high food quantity.
2. A model including both metabolism and growth indicates that consumer growth should differ between foods of high vs. low phosphorus concentration only when food quantity is above a certain level. Thus, two foods might give identical consumer growth rates at low food quantity but give different consumer growth at higher quantity.
3. Solution of the model using parameters based on 2 mm Daphnia compared with a survey of C and P in seston of marine and freshwater sites supports earlier conclusions of the potential importance of food quality constraints on Daphnia growth.     

Leptin inhibits food-deprivation-induced increases in food intake and food hoarding

Food deprivation stimulates foraging and hoarding and to a much lesser extent, food intake in Siberian hamsters. Leptin, the anorexigenic hormone secreted primarily from adipocytes, may act in the periphery, the brain, or both to inhibit these ingestive behaviors. Therefore, we tested whether leptin given either intracerebroventricularly or intraperitoneally, would block food deprivation-induced increases in food hoarding, foraging, and intake in animals with differing foraging requirements. Hamsters were trained in a running wheel-based food delivery foraging system coupled with simulated burrow housing. We determined the effects of food deprivation and several peripheral doses of leptin on plasma leptin concentrations. Hamsters were then food deprived for 48 h and given leptin (0, 10, 40, or 80 microg ip), and additional hamsters were food deprived for 48 h and given leptin (0, 1.25, 2.5, or 5.0 microg icv). Foraging, food intake, and hoarding were measured postinjection. Food deprivation stimulated food hoarding to a greater degree and duration than food intake. In animals with a foraging requirement, intracerebroventricular leptin almost completely blocked food deprivation-induced increased food hoarding and intake, but increased foraging. Peripheral leptin treatment was most effective in a sedentary control group, completely inhibiting food deprivation-induced increased food hoarding and intake at the two highest doses, and did not affect foraging at any dose. Thus, the ability of leptin to inhibit food deprivation-induced increases in ingestive behaviors differs based on foraging effort (energy expenditure) and the route of administration of leptin administration.     

MTII attenuates ghrelin- and food deprivation-induced increases in food hoarding and food intake

Food deprivation triggers a constellation of physiological and behavioral changes including increases in peripherally-produced ghrelin and centrally-produced agouti-related protein (AgRP). Upon refeeding, food intake is increased in most species, however hamsters primarily increase food hoarding. Food deprivation-induced increases in food hoarding by Siberian hamsters are mimicked by peripheral ghrelin and central AgRP injections. Because food deprivation stimulates ghrelin as well as AgRP synthesis/release, food deprivation-induced increases in hoarding may be mediated by melanocortin 3 or 4 receptor (MC3/4-R) antagonism via AgRP, the MC3/4-R inverse agonist. Therefore, we asked: Can a MC3/4-R agonist block food deprivation- or ghrelin-induced increases in foraging, food hoarding and food intake? This was accomplished by injecting melanotan II (MTII), a synthetic MC3/4-R agonist, into the 3rd ventricle in food deprived, fed or peripheral ghrelin injected hamsters and housed in a running wheel-based food delivery foraging system. Three foraging conditions were used: a) no running wheel access, non-contingent food, b) running wheel access, non-contingent food or c) a foraging requirement for food (10 revolutions/pellet). Food deprivation was a more potent stimulator of foraging and hoarding than ghrelin. Concurrent injections of MTII completely blocked food deprivation- and ghrelin-induced increases in food intake and attenuated, but did not always completely block, food deprivation- and ghrelin-induced increases in food hoarding. Collectively, these data suggest that the MC3/4-R are involved in ghrelin- and food deprivation-induced increases in food intake, but other neurochemical systems, such as previously demonstrated with neuropeptide Y, also are involved in increases in food hoarding as well as foraging.     

Trophic niche differences between coexisting omnivores silver carp and bighead carp in a pelagic food web

Understanding how omnivorous consumers are affected by their resources and how this is expressed through the food chain is a fundamental issue in ecology. We used stable isotope analysis of archived scales of two pelagic single-chain omnivorous fish species, bighead carp (Hypophthalmichthys nobilis) and silver carp (H. molitrix), to reconstruct historical trophic interactions patterns along a gradient of resources. We found that, although bighead carp and silver carp utilize the similar resources from the pelagic food chain, they can coexist and persist not only by regulating their trophic position and trophic dissimilarity, but also by regulating trophic niche width. Omnivorous fish often exhibit flexible foraging strategies, which is closely related to the availability of ecologic context. We found a positive relationship between trophic dissimilarity and zooplankton density, which may indicate that the competitive interactions induce strong top-down effects on zooplankton, and/or that high zooplankton availability release the between-population trophic interaction through bottom-up effect. The trophic niche width of bighead carp was positively related with zooplankton availability, probably reflecting that the niche of an omnivore at a higher trophic position is more sensitive to high quality resources. Our results indicate how different aspects of the trophic partitioning of coexisting omnivores may be regulated by different ecological contexts. These alternatives are not mutually exclusive and further theoretical work should include both these mechanisms to re-evaluate the effects of omnivory on food web properties.     

Intracerebroventricular beta-endorphin increases food intake of rats

B-Endorphin (B-END), met-enkepalin (M-ENK), and DAla²NMe⁵-met-enkephalinamide were administered intracerebroventricularly to rats and effects on the ingestion of a liquid diet were examined. B-END significantly increased food intake in a half-hour test at a dose of 200 ng/rat. Lower or higher doses did not affect food intake. Neither M-ENK or the synthetic enkephalin analog affected ingestion of the liquid diet. These findings demonstrate rapid action of an endorphin on food intake administered at a lower dose than has previously been reported and suggest a specificity for B-END in the endorphinergically mediated hyperphagic response.     

Potential food resources available to malleefowl Leipoa ocellata in marginal mallee lands during drought

Abstract Prime mallee lands that once supported high densities of malleefowl, Leipoa ocellata in New South Wales have been extensively cleared for agriculture. Malleefowl are now restricted largely to more and habitat. Given the added competition from introduced herbivores, there is concern that these marginal habitats may not contain sufficient food resources to support viable populations of malleefowl, particularly in times of drought. An opportunistic feeding strategy and omnivorous diet enable malleefowl to exploit a diverse array of food items. Vegetative and invertebrate food resources available to malleefowl in marginal mallee lands were monitored over a period of 1 year during drought. Food resources were varied, transient and patchily distributed. Composition and abundance fluctuated considerably, but potential food was never entirely absent. Despite the prevailing drought, food was obtainable throughout the year provided malleefowl adapted to the fluctuating availability of each of the various potential food resources. Reduced food resources in marginal habitat is not implicated as a major factor in the demise of the malleefowl. Food was most abundant between August and November, inclusive, due largely to the abundance of herbs, the diverse supply of buds, flowers and fruit on perennial shrubs, and the sporadic proliferation of cockroaches. Food availability was least, and therefore most critical, during February, March and June. The most favourable time of the year, in terms of available food resources, for the release of captive-bred individuals was during spring, around September.     

High hunger state increases olfactory sensitivity to neutral but not food odors

Understanding how hunger state relates to olfactory sensitivity has become more urgent due to their possible role in obesity. In 2 studies (within-subjects: n = 24, between-subjects: n = 40), participants were provided with lunch before (satiated state) or after (nonsatiated state) testing and completed a standardized olfactory threshold test to a neutral odor (Experiments 1 and 2) and discrimination test to a food odor (Experiment 2). Experiment 1 revealed that olfactory sensitivity was greater in the nonsatiated versus satiated state, with additionally increased sensitivity for the low body mass index (BMI) compared with high BMI group. Experiment 2 replicated this effect for neutral odors, but in the case of food odors, those in a satiated state had greater acuity. Additionally, whereas the high BMI group had higher acuity to food odors in the satiated versus nonsatiated state, no such differences were found for the low BMI group. The research here is the first to demonstrate how olfactory acuity changes as a function of hunger state and relatedness of odor to food and that BMI can predict differences in olfactory sensitivity.     

Feeding hungry neurons: astrocytes deliver food for thought

Among the proposed roles for astrocytes in the CNS is nutritive support for neurons. In this issue of Neuron, Voutsinos-Porche et al. provide evidence that astrocyte uptake of synaptic glutamate triggers astrocytic glycolysis and release of lactate, which in turn nourishes neurons and sustains neuronal activity.     

Feeding the extra billions: strategies to improve crops and enhance future food security

The ability to feed an expanding world population poses one of the greatest challenges to mankind in the future. Accompanying the increased demand for food by the expected nine billion inhabitants of Earth in 2050 will be a continual decrease in arable land area, together with a decline in crop yield due to a variety of stresses. For these formidable challenges to be met, future crops should not only by high-yielding, but also stress-tolerant and disease-resistant. In this review, we highlight the importance of genetic engineering as an indispensable tool to generate just such future crops. We briefly discuss strategies and available tools for biotechnological crop improvement and identify selected examples of candidate genes that may be manipulated so that current biological maxima in yield may be surpassed by comfortable margins. Future prospects and the necessity for basic research aimed at identifying novel target genes are also discussed.     

Feeding of lovastatin to rats increases the activity of the hepatic mitochondrial outer carnitine palmitoyltransferase

Administration of lovastatin to male, Sprague-Dawley rats by addition of the drug to the normal chow diet caused a two-fold increase in the activity of the hepatic mitochondrial outer carnitine palmitoyltransferase, but lovastatin apparently did not affect the sensitivity of the outer carnitine palmitoyltransferase to inhibition by malonyl-CoA. There was also no effect of lovastatin on the activity of the hepatic mitochondrial inner carnitine palmitoyltransferase. Feeding of cholestyramine to rats did not affect either the mitochondrial outer carnitine palmitoyltransferase or the mitochondrial inner carnitine palmitoyltransferase.     

Clonidine increases food and protein consumption in rats

Rats were given clonidine or its diluent, and allowed to eat freely from two isocaloric diets that differred in protein or carbohydrate content. Low clonidine doses (25–50 μg/kg) significantly increased total food and protein intake by rats given access to a high and a low protein diet. Several pairs of diets, differing in protein contents, were tested; clonidine's effect was greatest when a diet containing 30–45% protein was paired with one that was very low (5%) in protein. Higher clonidine doses (200 μg/kg) failed to modify either total food or protein intake. Clonidine had no effects on food or nutrient intake among animals given access to diets that differed in carbohydrate content (25 or 70% carbohydrate, plus 25% protein). In rats given access to only one diet, clonidine administration decreased food consumption when the diet was low in protein (5%), but increased consumption when the diet contained 25 or 50% protein. These data suggest that central noradrenergic synapses participate in the mechanisms controlling appetites for proteins. Clonidine may enhance protein intake by stimulating presynaptic alpha receptors, thus diminishing central noradrenergic tone. This effect on noradrenergic transmission is probably partly overcome by protein consumption, which increases brain tyrosine levels and thus can accelerate norepinephrine synthesis. Clonidine or related drugs may be useful clinically in treating diseases characterized by impaired appetite or increased need for protein.     

Ghrelin increases the motivation to eat, but does not alter food palatability

Homeostatic eating cannot explain overconsumption of food and pathological weight gain. A more likely factor promoting excessive eating is food reward and its representation in the central nervous system (CNS). The anorectic hormones leptin and insulin reduce food reward and inhibit related CNS reward pathways. Conversely, the orexigenic gastrointestinal hormone ghrelin activates both homeostatic and reward-related neurocircuits. The current studies were conducted to identify in rats the effects of intracerebroventricular ghrelin infusions on two distinct aspects of food reward: hedonic valuation (i.e., "liking") and the motivation to self-administer (i.e., "wanting") food. To assess hedonic valuation of liquid food, lick motor patterns were recorded using lickometry. Although ghrelin administration increased energy intake, it did not alter the avidity of licking (initial lick rates or lick-cluster size). Several positive-control conditions ruled out lick-rate ceiling effects. Similarly, when the liquid diet was hedonically devalued with quinine supplementation, ghrelin failed to reverse the quinine-associated reduction of energy intake and avidity of licking. The effects of ghrelin on rats' motivation to eat were assessed using lever pressing to self-administer food in a progressive-ratio paradigm. Ghrelin markedly increased motivation to eat, to levels comparable to or greater than those seen following 24 h of food deprivation. Pretreatment with the dopamine D1 receptor antagonist SCH-23390 eliminated ghrelin-induced increases in lever pressing, without compromising generalized licking motor control, indicating a role for D1 signaling in ghrelin's motivational feeding effects. These results indicate that ghrelin increases the motivation to eat via D1 receptor-dependent mechanisms, without affecting perceived food palatability.     

Feeding increases 5-hydroxytryptamine and norepinephrine within the hypothalamus of chicks

It is thought that hypothalamic 5-hydroxytryptamine (5HT) and norepinephrine (NE) are involved in the regulation of feeding in chicks. The present study was conducted to elucidate changes in the levels of extracellular 5HT and NE in the hypothalamus during feeding of chicks. In order to measure 5HT, NE and 4-hydroxy-3-methoxyphenylglycol (MHPG), which is a major metabolite of NE, we used brain microdialysis and high-pressure liquid chromatography with an electrochemical detector. After collecting samples to determine the basal levels of 5HT, NE and MHPG, food-deprived birds were given access to food. 5HT levels in the medial hypothalamus (MH) and lateral hypothalamus (LH) increased during the first 30 min of feeding, and then returned to basal levels. NE and MHPG in the LH increased during feeding, and remained elevated throughout the experiment. This study supports an idea that hypothalamic monoamines in the chick brain are involved in the regulation of feeding.