Orexins and feeding: special occasions or everyday occurrence?

Neurons expressing prepro-orexin, the precursor of orexin-A and -B, are found in the lateral hypothalamic area, a region classically implicated in driving feeding. Orexin-A induces feeding transiently when injected centrally, and food intake can be decreased when orexin action is disrupted by immunoneutralization of orexin-A, or by pharmacological blockade of orexin receptors, or by transgenic knockout of orexin. Here, we argue that orexin neurons may act to stimulate feeding in the short term, and that important regulatory signals may be a fall in plasma glucose (stimulatory), countered by satiety signals generated by eating, such as gastric distention (inhibitory).     

Can suspension feeding by bivalves regulate phytoplankton biomass in Lake Waccamaw, North Carolina?

Suspension feeding by bivalves has been hypothesized to control phytoplankton biomass in shallow aquatic ecosystems. Lake Waccamaw, North Carolina, USA is a shallow lake with a diverse bivalve assemblage and low to moderate phytoplankton biomass levels. Filtration and ingestion rates of two relatively abundant species in the lake, the endemic unionid, Elliptio waccamawensis, and an introduced species, Corbicula fluminea, were measured in experiments using natural phytoplankton for durations of 1 to 6 days. Measured filtration and ingestion rates averaged 1.78 and 1.121 ind.^–1 d^–1, much too low to control phytoplankton at the observed phytoplankton biomass levels and growth rates. Measured ingestion rates averaged 4.80 and 1.50 µg chlorophyll a ind.^–1 d^–1, too low to support individuals of either species. The abundance of benthic microalgae in Lake Waccamaw reaches 200 mg chlorophyll a m^–2 in the littoral zone and averages almost an order of magnitude higher than depth-integrated phytoplankton chlorophyll a. Total microalgal biomass in the lake is therefore not controlled by suspension feeding by bivalves.     

Blood feeding patterns of mosquitoes: random or structured?

Background

During the non-breeding period, many birds migrate to milder areas, found closer to the equator than their breeding sites. Opposite movements are very rare. In the Southern Ocean, the abundance of ¹³C declines markedly with more southern latitude, providing a characteristic ¹³C isoscape. This can be used as a tracer for the movement of seabirds between breeding and inter-breeding areas, by comparing stable isotope ratios of feathers grown at different times of the year.

Results

We studied seasonal movements of Thin-billed prions (Aves, Procellariiformes), breeding at the Subantarctic Falkland/Malvinas Islands, compared with those of Wilson's storm-petrels breeding in the Antarctic South Shetland Islands. The two species showed opposite migratory movements. While Wilson's storm-petrels moved to warmer waters north of the Drake Passage in winter, Thin-billed prions showed a reversed movement towards more polar waters. Carbon stable isotope ratios in recent and historical feathers indicated that poleward winter movements of Thin-billed prions were less common historically (45% in 1913-1915), and have only recently become dominant (92% in 2003-2005), apparently in response to warming sea temperatures.

Conclusions

This study shows that pelagic seabirds can rapidly change migration strategies within populations, including migration towards more poleward waters in winter.     

Vertical stratification of feeding by Japanese beetles within linden tree canopies: selective foraging or height per se?

Adult Japanese beetles, Popillia japonica Newman (Coleoptera: Scarabaeidae), tend to aggregate and feed most heavily in the upper canopy of host plants, defoliating them from the top down. We examined characteristics of linden (Tilia cordata L.) foliage from different canopy zones and tested two hypotheses that might account for vertical stratification of feeding by this vagile, polyphagous folivore. In the field, P. japonica caused 4–12 times more damage to upper canopy leaves in full sunlight than to lower canopy leaves in sun or shade. However, this within-tree pattern apparently cannot be explained by differences in nutritional parameters (protein, water, and sugar content) or defensive properties (toughness, tannins) of leaves. Furthermore, beetles did not discriminate between foliage from different canopy zones in laboratory choice tests, nor were fecundity or longevity higher for beetles fed upper canopy, sun-exposed leaves. Clonal grape plants suspended from vertical posts in the field at 3.65, 1.83 or 0 m above ground showed a top-down defoliation pattern identical to that seen in linden trees. This suggests that the height of foliage per se strongly affects initial orientation and attack by P. japonica. Recent related studies have shown that both sexes of P. japonica are strongly attracted to host volatiles induced by feeding of conspecific beetles. We suggest that Japanese beetles begin to feed in the upper canopy for reasons unrelated to host nutritional variation (e.g., behavioral thermoregulation, visual orientation to the host silhouette), and that top-down defoliation follows as additional beetles are attracted to feeding-induced volatiles acting as aggregation kairomones.     

Phycotoxin accumulation in zooplankton feeding on Alexandrium fundyense--vector or sink?

Zooplankton can consume toxic Alexandrium spp. dinoflagellatesin the Gulf of Maine and retain paralytic shellfish poisoning(PSP) toxins, potentially acting as toxin vectors. We performedexperiments to determine toxin budgets for common species ofcopepods (Acartia hudsonica, Eurytemora herdmani, Centropageshamatus) feeding on toxic Alexandrium fundyense, offered asmonocultures or in mixtures of algal prey, by comparing calculatedtoxin ingestion rates and toxin content of copepod body tissueand fecal pellets. When fed monocultures, both copepod tissueand fecal pellet fractions accounted for 5% each of the calculatedingested toxin, and thus by difference 90% was lost as a dissolvedfraction into the seawater medium. The presence of alternativefood did not significantly alter the efficiency of toxin retention.Sloppy feeding or regurgitation are probable mechanisms forrelease of toxin to sea water. Experiments using varying concentrationsof A. fundyense and alternativenon-toxic species did not showsignificant effects of cell concentration on toxin retentionefficiency. Total toxin retained and efficiency of retentionvaried among copepod species. Toxin profiles (% molar composition)of dinoflagellates, copepod tissues and fecal pellets differedslightly, suggesting some metabolic transformation. Becauseof their low retention efficiency, copepod grazers can effectivelydisperse PSP toxins produced by Alexandrium spp. into the environment,where they are much less likely to be harmful—zooplanktonact as a sink for PSP toxins. Nevertheless, sufficient toxinbody burdens are attained to contribute to propagation of PSPtoxins to other trophic levels.     

Feeling by sight or seeing by touch?

We have addressed the role of occipital and somatosensory cortex in a tactile discrimination task. Sight-ed and congenitally blind subjects rated the roughness and distance spacing for a series of raised dot patterns. When judging roughness, intermediate dot spacings were perceived as being the most rough, while distance judgments generated a linear relation. Low-frequency rTMS applied to somatosensory cortex disrupted roughness without affecting distance judgments, while rTMS to occipital cortex disrupted distance but not roughness judgments. We also tested an early blind patient with bilateral occipital cortex damage. Her performance on the roughness determination task was normal; however, she was greatly impaired with distance judgments. The findings suggest a double-dissociation effect in which roughness and distance are primarily processed in somatosensory and occipital cortex, respectively. The differential effect of rTMS on task performance and corroborative clinical evidence suggest that occipital cortex is engaged in tactile tasks requiring fine spatial discrimination.     

Nectarivory by the plant-tissue feeding predator Macrolophus pygmaeus Rambur (Heteroptera: Miridae): Nutritional redundancy or nutritional benefit?

Most predators and parasitoids feed on plant-provided food (nectar, pollen) or engage in herbivory during at least part of their life stages. Plant feeding by these insects plays an important role in driving predator-herbivore dynamics. Thus, understanding the effects of plant feeding on omnivores could be an important element in improving biological control strategies. The mirid Macrolophus pygmaeus is an omnivorous heteropteran predator of whitefly and other pests. Unlike other predators that need to seek out accessible nectar to meet their carbohydrate requirements, mirid bugs can access the plant's carbohydrate resources by feeding directly on plant tissues. Leaf and stem feeding could be seen as a nutritional surrogate that allows mirids to become independent of nectar availability. However, to date feeding experiments have not yet considered nectar feeding by these mirid predators. In this study we demonstrate that M. pygmaeus survival is prolonged on broad bean plants featuring extrafloral nectar as compared to broad bean with extrafloral nectaries removed, irrespective of the presence of cattail pollen. Survival on extrafloral nectar was comparable to the survival by individuals kept on broad bean provided with eggs of Ephestia kuehniella as prey. Also, a greater proportion of mirid females laid eggs when extrafloral nectar was available as compared to those confined on nectariless plants without supplemental food.     

Sap feeding by the marsupial Petaurus australis: an enigmatic behaviour?

Summary The Yellow-bellied Glider, Petaurus australis, was observed to feed sporadically but extensively on eucalypt sap. Gliders extracted sap by making incisions into the bark with their procumbent lower incisor teeth and licking the resulting exudate. Less than 1% of possible trees were incised for sap. Sap flow and sap-sugar concentration were estimated for eight sap-site trees and eight non sap-site trees at intervals during an 18 month period. Measurements of sap-sugar concentration differed substantially among trees but fluctuated between sample periods independent of glider use. Sap flow measurements, were always higher for those trees currently in use by gliders, although the particular sap-site trees comprising this group varied between sample periods. The variation in sap flow occurred indenpendent of the incidence of rainfall or the type of microhabitat the tree occupied. Experimental incising of trees, designed to mimic the effects of feeding by gliders, failed to show any effect on sap flow. This suggests that the incidence of sap feeding is determined by a tree's pattern of sap flow and that there may be trees with unusual patterns of sap flow which gliders select as the most favourable trees to incise.     

Nuptial feeding by male bushcrickets: an indicator of male quality?

Male bushcrickets transfer a spermatophore at mating that consistsof a sperm-containing ampulla and a product of the accessoryglands, the spermatophylax, that is consumed by the female duringinsemination. Male Requena verticalis produce functionally differentspermatophores depending on the availability of sexually receptivefemales. They will maintain high mating frequency by providinga gift sufficient to ensure sperm transfer, or will invest parentallyin females when their mating frequency is low. We examined therelationship between male quality and nuptial feeding underconditions where males invest in ejaculate protection or inparental investment. When investing in ejaculate protection,males reduced the quality of the spermatophylax meal by reducingboth the concentration of protein and the absolute amount ofprotein it contained. There was no relationship between malephenotype and gift size or quality. Moreover, we could findno evidence for the recently advanced hypothesis that femalescan exercise mate choice by interfering with insemination. However,when males were investing parentally, we found a positive associationbetween spermatophylax size and male size, but no relationshipbetween protein content and male size. Males with high levels offluctuating asymmetry invested more heavily in the nutritionalcontent of their spermatophylaxes than did symmetrical males.Thus, male quality does influence nuptial feeding, but in amanner predicted by a model of indirect fitness benefits frommate choice.     

Primate Communication: By Nature Honest, or by Experience Wise?

We review evolutionary views on honesty and deception and their application to studies of nonhuman primate communication. There is evidence that some primate signals are likely to be accurate on the basis of costliness. They appear most often in contexts that include overtly competitive interactions in which unrelated individuals have limited access to information about one another. However, both game theoretic models and most empirical work suggest that costly signals are not often likely to be the basis for honest communication in nonhuman primates. Inexpensive signaling can exist in contexts wherein communication occurs among related animals, something common among many nonhuman primate societies. Another condition in which inexpensive signaling is possible and that is also typical of nonhuman primates, is when sender and receiver both benefit from coordinated interactions. Additionally, when individuals interact repeatedly and can use past interactions to assess the honesty of signals and to modify future response to signals, low-cost signals can evolve. Nonhuman primates appear to deal with the problem of deception via skeptical responding, which can be largely accounted for by learning rules and the fact that they live in stable social groups and can recognize one another and recall past interactions.     

Death by chaperone: HSP90, HSP70 or both?

HSP70 family members are highly conserved proteins that function as molecular chaperones. Their principle role is to aid protein folding and promote the correct cellular localisations of their respective substrates. The function of HSP70 isoforms can be exhibited independently or with the HSP90 chaperone system in which HSP70 is important for substrate recruitment. In addition to their chaperone role, HSP70 isoforms promote cell survival by inhibiting apoptosis at multiple points within both the intrinsic and extrinsic cell death pathways. Consistent with this cytoprotective function, increased expression of HSP70 isoforms is commonly associated with the malignant phenotype. We recently reported that dual silencing of the major constitutive (HSC70) and inducible (HSP72) isoforms of HSP70 in cancer cells could phenocopy the effects of a pharmacologic HSP90 inhibitor to induce proteasome-dependent degradation of HSP90 client proteins CRAF, CDK4 and ERBB2. This was accompanied by a G1 cell cycle arrest and extensive apoptosis which was not seen in non-tumorigenic human cell lines. Here we discuss the possible implications of our research for the development of HSP70 family modulators which offer not only the possibility of inhibiting HSP70 activity but also the simultaneous inhibition of HSP90, resulting in extensive tumour-specific apoptosis.     

Entrainment of circadian rhythms of cholesterol‐LDL,corticosterone and motor activity by feeding schedules in rats

Abstract

The daily variations of locomotor activity, plasma and adrenal corticosterone levels and cholesterol‐LDL were studied in male Wistar rats with food ad libitum and feeding restricted to the first 4 hours of the light phase in LD 12:12..

Under LD 12:12 (light on from 9:00 to 21:00h) rats with food ad libitum were eating and moving during the dark period and the locomotor activity clearly showed a biphasic pattern with three harmonic components. Plasma and adrenal corticosterone levels increased during the light period and reached a maximum value just before the dark period whereas the acrophase of cholesterol‐LDL is found at the beginning of the light phase.

The acrophases of activity, plasma and adrenal corticosterone levels in the restricted feeding schedule rats occurred in the first three hours of lighting and the cholesterol‐LDL acrophase at the beginning of the dark phase.

These results confirm a previous report that the shift of feeding to the light phase seems to cause a concomitant phase‐shift in all the variables measured.     

Running on empty? Freshwater feeding by spawning anadromous alewife Alosa pseudoharengus

Anadromous alewife Alosa pseudoharengus (n = 202; mean ± s.d . fork length = 231 ± 14 mm) were captured from 10 May to 27 June 2018 in an upper watershed lake on the Isthmus of Chignecto, Canada (45°57′N, 64°14′W). Thirty individuals (mean ± s.d. fork length = 250 ± 12 mm) were captured in an adjacent estuary downstream of a tide gate on 25 April 2018. Comparing estuarine to freshwater specimens, mean gonad mass and gonadosomatic indices in males and females decreased approximately 40% and 60%, and 31% and 50%, respectively. Individuals were characterized as pre-spawners in the estuary and spawners in the lake. Males maintained similar body condition throughout the spawning run whereas female condition decreased 9.4% between the estuary and lake. Stomach fullness decreased comparing estuarine and freshwater specimens, yet 93% of stomachs examined from individuals captured in the lake contained prey. Most males fed throughout all spawning stages (3%–17% empty stomachs), while all females fed during pre- and post-spawning stages and some fasted during spawning (11% empty stomachs). Cumulative prey curve never reached an asymptote, either weekly or for the entire sampling period, so freshwater diet may not have been completely described. Calanoid copepods (79.3%I_A) were a diet staple, with the secondary prey of mayfly nymphs (O. Ephemeroptera) consumed more by females (13.6%I_A) than males (6.2%I_A). PERMANOVA and PERMDISP analyses revealed significant dietary differences in freshwater were weekly and not due to dispersion effects, thus most likely due to feeding on various development stages of insect species. Our results challenge the long-held paradigm that anadromous A. pseudoharengus fast during the spawning migration.     

Winter severity or supplementary feeding—which matters more for wild boar?

During recent decades, wild boar have successfully colonised areas previously believed to be unsuitable for the species. Estonia lies close to the northern limit of the species range, and mast foods, which are a common natural food source for many wild boar populations, are practically absent. We hypothesised that the proportion of cultivated area and especially supplementary feeding, which is widely used in Estonia to lower the winter mortality of game species, play important roles in sustaining the local wild boar population. To determine the most important factors shaping the abundance of wild boar in a northern environment, we developed mixed models to account for variation in an index of wild boar abundance (AI) based on winter track counts. The abundance of supplementary feeding sites and mean January temperature were the most important factors determining wild boar winter abundance. We conclude that the current high local population density is sustained by intensive supplementary feeding, which has exceeded the limiting effect of harsh winters.     

Are barricading and neighbor burrow-plugging by male crabs ofIlyoplax pusilla (Crustacea: Brachyura: Ocypodidae) related to feeding or mating?

Large males ofIlyoplax pusilla engage in 2 unique antineighbor behaviors, i.e., the building of a barricade of mud close to the neighbor's burrow, and plugging the entrance of the neighbor's burrow with mud. Correlation of these two behaviors to other behaviors was studied through field observations. Burrow-plugging was more frequent in May–June, when males waved actively, than in August, when waving was less frequent but foraging activity was higher. Frequency of daily burrow-plugging activity correlated well with that of waving, but not with that of foraging. These data suggest that burrowplugging is related to reproductive activities rather than feeding. The relationship of barricading to either waving or feeding was unclear.     

Paradoxes of tumour complexity: somatic selection,vulnerability by design,or infectious aetiology?

The aetiology of cancer involves intricate cellular and molecular mechanisms that apparently emerge on the short timescale of a single lifetime. Some of these traits are remarkable not only for their complexity, but also because it is hard to conceive selection pressures that would favour their evolution within the local competitive microenvironment of the tumour. Examples include ‘niche construction’ (re‐programming of tumour‐specific target sites) to create permissive conditions for distant metastases; long‐range feedback loops of tumour growth; and remarkably ‘plastic’ phenotypes (e.g. density‐dependent dispersal) associated with metastatic cancer. These traits, which we term ‘paradoxical tumour traits’, facilitate the long‐range spread or long‐term persistence of the tumours, but offer no apparent benefit, and might even incur costs in the competition of clones within the tumour. We discuss three possible scenarios for the origin of these characters: somatic selection driven by specific selection regimes; non‐adaptive emergence due to inherent vulnerabilities in the organism; and manipulation by putative transmissible agents that contribute to and benefit from these traits. Our work highlights a lack of understanding of some aspects of tumour development, and offers alternative hypotheses that might guide further research.     

Altered drug translocation mediated by the MDR protein: Direct,indirect, or both?

Overexpression of the MDR protein, or p-glycoprotein (p-GP), in cells leads to decreased initial rates of accumulation and altered intracellular retention of chemotherapeutic drugs and a variety of other compounds. Thus, increased expression of the protein is related to increased drug resistance. Since several homologues of the MDR protein (CRP, ltpGPA, PDR5, sapABCDF) are also involved in conferring drug resistance phenomena in microorganisms, elucidating the function of the MDR protein at a molecular level will have important general applications. Although MDR protein function has been studied for nearly 20 years, interpretation of most data is complicated by the drug-selection conditions used to create model MDR cell lines. Precisely what level of resistance to particular drugs is conferred by a given amount of MDR protein, as well as a variety of other critical issues, are not yet resolved. Data from a number of laboratories has been gathered in support of at least four different models for the MDR protein. One model is that the protein uses the energy released from ATP hydrolysis to directly translocate drugs out of cells in some fashion. Another is that MDR protein overexpression perturbs electrical membrane potential () and/or intracellular pH (pH_i) and therebyindirectly alters translocation and intracellular retention of hydrophobic drugs that are cationic, weakly basic, and/or that react with intracellular targets in a pH_i, or -dependent manner. A third model proposes that the protein alternates between drug pump and Cl^– channel (or channel regulator) conformations, implying that both direct and indirect mechanisms of altered drug translocation may be catalyzed by MDR protein. A fourth is that the protein acts as an ATP channel. Our recent work has tested predictions of these models via kinetic analysis of drug transport and single-cell photometry analysis of pH_i, , and volume regulation in novel MDR and CFTR transfectants that have not been exposed to chemotherapeutic drugs prior to analysis. This paper reviews these data and previous work from other laboratories, as well as relevant transport physiology concepts, and summarizes how they either support or contradict the different models for MDR protein function.