The neurogenetics and evolution of food-related behaviour

AN, Johnson AJ, Govindan B, Baby S. Flower-fruit dynamics, visitor-predator patterns and chemical preferences in the tropical bamboo, Melocanna baccifera

Mast seeding and associated events in Melocanna baccifera, the largest fruit producing bamboo, is an enigma. So far there are no comprehensive accounts on its flowering phenology, fruiting dynamics and animal interactions. In this study, spanning over 13 years (2009 to 2022), we observed eight M. baccifera clumps in JNTBGRI Bambusetum from flowering initiation, fruiting to eventual death. Flowering phenology, floral characteristics, floret types, breeding system, bee visitation, pollination, fruit production and predators were recorded; predation patterns were correlated with fruit chemistry. Flowering duration of clumps ranged from 20 (March 2009-October 2010) to 120 (September 2012-August 2022) months. Bisexual florets are dichogamous and protogynous; and female duration (22-72 h) is many times higher than male duration (2-6 h). The highest ever fruit production for an individual bamboo clump (456.67 Kg) was recorded. Of the total fallen fruits (38371), 38.11% were predated, 43.80% good fruits (no predator hits) and 18.09% immature fruits. A positive correlation between reward (fruits) versus predation was observed, especially in short intervals of high fruit production. Pollen predators (Apis cerana indica, Halictus taprabonae, Braunsapis cupulifera, Trigona iridipennis), fruit predators, ranging from arthropods to mammals, viz., millipede (Spinotarsus colosseus), slug (Mariaella dussumieri), snails (Cryptozona bistrialis, Macrochlamys sp.), borers (Achroia grisella, Blattella germanica), mammals (monkeys Macaca radiata, rats Rattus rattus, porcupine Hystrix indica, wild boar Sus scrofa, palm civet Paradoxurus hermaphroditus), seedling predators (rabbit Lepus nigricollis, deer Axis axis), and insect/pest predators (ants Crematogaster biroi, Oecophylla smaragdina, mantis Euchomenella indica) were identified. Fruit predation is linked to its age and chemistry. Apart from new insights on flowering phenology, breeding system, pollination and fruiting dynamics, this study demonstrates the vibrant interaction between M. baccifera flowers/fruits and visitors/predators, and provides significant leads towards elucidating the cause of rat multiplication and other events associated with its gregarious flowering.

The FMRFamide Neuropeptide FLP-20 Acts as a Systemic Signal for Starvation Responses in Caenorhabditis elegans

Most animals face frequent periods of starvation throughout their entire life and thus need to appropriately adjust their behavior and metabolism during starvation for their survival. Such adaptive responses are regulated by a complex set of systemic signals, including hormones and neuropeptides. While much progress has been made in identifying pathways that regulate nutrient-excessive states, it is still incompletely understood how animals systemically signal their nutrient-deficient states. Here, we showed that the FMRFamide neuropeptide FLP-20 modulates a systemic starvation response in Caenorhabditis elegans. We found that mutation of flp-20 rescued the starvation hypersensitivity of the G protein β-subunit gpb-2 mutants by suppressing excessive autophagy. FLP-20 acted in AIB neurons, where the metabotropic glutamate receptor MGL-2 also functions to modulate a systemic starvation response. Furthermore, FLP-20 modulated starvation-induced fat degradation in a manner dependent on the receptor-type guanylate cyclase GCY-28. Collectively, our results reveal a circuit that senses and signals nutrient-deficient states to modulate a systemic starvation response in multicellular organisms.

The foraging gene as a modulator of division of labour in social insects

The social ants, bees, wasps, and termites include some of the most ecologically-successful groups of animal species. Their dominance in most terrestrial environments is attributed to their social lifestyle, which enable their colonies to exploit environmental resources with remarkable efficiency. One key attribute of social insect colonies is the division of labour that emerges among the sterile workers, which represent the majority of colony members. Studies of the mechanisms that drive division of labour systems across diverse social species have provided fundamental insights into the developmental, physiological, molecular, and genomic processes that regulate sociality, and the possible genetic routes that may have led to its evolution from a solitary ancestor. Here we specifically discuss the conserved role of the foraging gene, which encodes a cGMP-dependent protein kinase (PKG). Originally identified as a behaviourally polymorphic gene that drives alternative foraging strategies in the fruit fly Drosophila melanogaster, changes in foraging expression and kinase activity were later shown to play a key role in the division of labour in diverse social insect species as well. In particular, foraging appears to regulate worker transitions between behavioural tasks and specific behavioural traits associated with morphological castes. Although the specific neuroethological role of foraging in the insect brain remains mostly unknown, studies in genetically tractable insect species indicate that PKG signalling plays a conserved role in the neuronal plasticity of sensory, cognitive and motor functions, which underlie behaviours relevant to division of labour, including appetitive learning, aggression, stress response, phototaxis, and the response to pheromones.

The genetic architecture of larval aggregation behavior in Drosophila

Many insect species exhibit basal social behaviors such as aggregation, which play important roles in their feeding and mating ecologies. However, the evolutionary, genetic, and physiological mechanisms that regulate insect aggregation remain unknown for most species. Here, we used natural populations of Drosophila melanogaster to identify the genetic architecture that drives larval aggregation feeding behavior. By using quantitative and reverse genetic approaches, we have identified a complex neurogenetic network that plays a role in regulating the decision of larvae to feed in either solitude or as a group. Results from single gene, RNAi-knockdown experiments show that several of the identified genes represent key nodes in the genetic network that determines the level of aggregation while feeding. Furthermore, we show that a single non-coding variant in the gene CG14205, a putative acyltransferase, is associated with both decreased mRNA expression and increased aggregate formation, which suggests that it has a specific role in inhibiting aggregation behavior. Our results identify, for the first time, the genetic components which interact to regulate naturally occurring levels of aggregation in D. melanogaster larvae.

Do terrestrial gastropods use olfactory cues to locate and select food actively?

Having been investigated for over 40 years, some aspects of the biology of terrestrial gastropod's olfactory system have been challenging and highly contentious, while others still remain unresolved. For example, a number of terrestrial gastropod species can track the odor of food, while others have no strong preferences toward food odor; rather they find it by random encounter. Here, while assessing the most recent findings and comparing them with earlier studies, the aspects of the food selection based on olfactory cues are examined critically to highlight the speculations and controversies that have arisen. We analyzed and compared the potential role of airborne odors in the feeding behavior of several terrestrial gastropod species. The available results indicate that in the foraging of most of the terrestrial gastropod species odor cues contribute substantially to food finding and selection. The results also suggest, however, that what they will actually consume largely depends on where they live and the species of gastropod that they are. Due to the voluminous literature relevant to this object, this review is not intended to be exhaustive. Instead, I selected what I consider to be the most important or critical in studies regarding the role of the olfaction in feeding of terrestrial gastropods.

Opposite effects of 5-HT/AKH and octopamine on the crop contractions in adult Drosophila melanogaster: Evidence of a double brain-gut serotonergic circuitry

This study showed that in adult Drosophila melanogaster, the type of sugar-either present within the crop lumen or in the bathing solution of the crop-had no effect on crop muscle contraction. What is important, however, is the volume within the crop lumen. Electrophysiological recordings demonstrated that exogenous applications of serotonin on crop muscles increases both the amplitude and the frequency of crop contraction rate, while adipokinetic hormone mainly enhances the crop contraction frequency. Conversely, octopamine virtually silenced the overall crop activity. The present study reports for the first time an analysis of serotonin effects along the gut-brain axis in adult D. melanogaster. Injection of serotonin into the brain between the interocellar area shows that brain applications of serotonin decrease the frequency of crop activity. Based on our results, we propose that there are two different, opposite pathways for crop motility control governed by serotonin: excitatory when added in the abdomen (i.e., directly bathing the crop) and inhibitory when supplied within the brain (i.e., by injection). Finally, our results point to a double brain-gut serotonergic circuitry suggesting that not only the brain can affect gut functions, but the gut can also affect the central nervous system. On the basis of our results, and data in the literature, a possible mechanism for these two discrete serotonergic functions is suggested.

Taotie neurons regulate appetite in Drosophila

The brain has an essential role in maintaining a balance between energy intake and expenditure of the body. Deciphering the processes underlying the decision-making for timely feeding of appropriate amounts may improve our understanding of physiological and psychological disorders related to feeding control. Here, we identify a group of appetite-enhancing neurons in a behavioural screen for flies with increased appetite. Manipulating the activity of these neurons, which we name Taotie neurons, induces bidirectional changes in feeding motivation. Long-term stimulation of Taotie neurons results in flies with highly obese phenotypes. Furthermore, we show that the in vivo activity of Taotie neurons in the neuroendocrine region reflects the hunger/satiety states of un-manipulated animals, and that appetitive-enhancing Taotie neurons control the secretion of insulin, a known regulator of feeding behaviour. Thus, our study reveals a new set of neurons regulating feeding behaviour in the high brain regions that represents physiological hunger states and control feeding behaviour in Drosophila.

Feeding control requires the integration and coordination of motivational, sensory and motor circuits in the brain. Here, the authors discover a set of neurons that regulate feeding in Drosophila by promoting insulin release, and whose activity reflects physiological hunger and satiety states of flies.

Kynurenic acid is a nutritional cue that enables behavioral plasticity

The kynurenine pathway of tryptophan metabolism is involved in the pathogenesis of several brain diseases, but its physiological functions remain unclear. We report that kynurenic acid, a metabolite in this pathway, functions as a regulator of food-dependent behavioral plasticity in C. elegans. The experience of fasting in C. elegans alters a variety of behaviors, including feeding rate, when food is encountered post-fast. Levels of neurally produced kynurenic acid are depleted by fasting, leading to activation of NMDA-receptor-expressing interneurons and initiation of a neuropeptide-y-like signaling axis that promotes elevated feeding through enhanced serotonin release when animals re-encounter food. Upon refeeding, kynurenic acid levels are eventually replenished, ending the elevated feeding period. Because tryptophan is an essential amino acid, these findings suggest that a physiological role of kynurenic acid is in directly linking metabolism to activity of NMDA and serotonergic circuits, which regulate a broad range of behaviors and physiologies.

Variables controlling entry into and exit from the steady-state, one of two modes of feeding in Aplysia

Background

Aplysia feeding is a model system for examining the neural mechanisms by which changes in motivational state control behavior. When food is intermittently present, Aplysia eat large meals controlled by a balance between food stimuli exciting feeding and gut stimuli inhibiting feeding. However, when food is continuously present animals are in a state in which feeding is relatively inhibited and animals eat little. We examined which stimuli provided by food and feeding initiate steady-state inhibition of feeding, and which stimuli maintain the inhibition.

Results

Multiple stimuli were found to control entry into the steady-state inhibition, and its maintenance. The major variable governing entry into the steady-state is fill of the gut with bulk provided by food, but this stimulus cannot alone cause entry into the steady-state. Food odor and nutritional stimuli such as increased hemolymph glucose and L-arginine concentrations also contribute to inhibition of feeding leading to entry into the steady-state. Although food odor can alone cause some inhibition of feeding, it does not amplify the effect of gut fill. By contrast, neither increased hemolymph glucose nor L-arginine alone inhibits feeding in hungry animals, but both amplify the inhibitory effects of food odor, and increased glucose also amplifies the effect of gut fill. The major variable maintaining the steady-state is the continued presence of food odor, which can alone maintain the steady-state for 48–72 hrs. Neither increased glucose nor L-arginine can alone preserve the steady-state, although they partially preserve it. Glucose and arginine partially extend the effect of food odor after 72 hrs.

Conclusions

These findings show that control of Aplysia feeding is more complex than was previously thought, in that multiple inhibitory factors interact in its control.

Presynaptic modulation of early olfactory processing in Drosophila

Most animals are endowed with an olfactory system that is essential for finding foods, avoiding predators, and locating mating partners. The olfactory system must encode the identity and intensity of behaviorally relevant stimuli in a dynamic environmental landscape. How is olfactory information represented? How is a large dynamic range of odor concentrations represented in the olfactory system? How is this representation modulated to meet the demands of different internal physiological states? Recent studies have found that sensory terminals are important targets for neuromodulation. The emerging evidence suggests that presynaptic inhibition scales with sensory input and thus provides a mechanism to increase dynamic range of odor representation. In addition, presynaptic facilitation could be a mechanism to alter behavioral responses in hungry animals. This review will focus on the GABA(B) (gamma-aminobutyric acid) receptor-mediated presynaptic inhibition, and neuropeptide-mediated presynaptic modulation in Drosophila.

Serotonin activates overall feeding by activating two separate neural pathways in Caenorhabditis elegans

Food intake in the nematode Caenorhabditis elegans requires two distinct feeding motions, pharyngeal pumping and isthmus peristalsis. Bacteria, the natural food of C. elegans, activate both feeding motions (Croll, 1978; Horvitz et al., 1982; Chiang et al., 2006). The mechanisms by which bacteria activate the feeding motions are largely unknown. To understand the process, we studied how serotonin, an endogenous pharyngeal pumping activator whose action is triggered by bacteria, activates feeding motions. Here, we show that serotonin, like bacteria, activates overall feeding by activating isthmus peristalsis as well as pharyngeal pumping. During active feeding, the frequencies and the timing of onset of the two motions were distinct, but each isthmus peristalsis was coupled to the preceding pump. We found that serotonin activates the two feeding motions mainly by activating two separate neural pathways in response to bacteria. For activating pumping, the SER-7 serotonin receptor in the MC motor neurons in the feeding organ activated cholinergic transmission from MC to the pharyngeal muscles by activating the Gsα signaling pathway. For activating isthmus peristalsis, SER-7 in the M4 (and possibly M2) motor neuron in the feeding organ activated the G(12)α signaling pathway in a cell-autonomous manner, which presumably activates neurotransmission from M4 to the pharyngeal muscles. Based on our results and previous calcium imaging of pharyngeal muscles (Shimozono et al., 2004), we propose a model that explains how the two feeding motions are separately regulated yet coupled. The feeding organ may have evolved this way to support efficient feeding.

Effect of serotonin and calcium on the supercontractile muscles of the adult blowfly crop

Bioassays and electrophysiological recordings were conducted to determine the role of serotonin and calcium on the supercontractile pump muscles of the diverticulated crop of adult blowflies. Using in situ crop preparations, serotonin was found to significantly increase the rates of contractions of a specific pump in the crop wall, pump P4. The addition of the serotonin antagonist, mianserin, or calcium free saline, both significantly reduced the contraction rates of this pump. Recordings, using suction electrodes from pump P4, confirm the in situ bioassay data and show that serotonin promotes muscle activity in empty crops in which no pump activity is normally observed. Moreover, our data indicate the crucial role of extracellular calcium ions in crop pump contractile activity. These results provide new information on how the crop of adult dipterans is modulated and suggest that serotonin, possibly supplied by neurons in the thoracico-abdominal neural plexus, may be involved in modulating the pumping of crop contents into the midgut for digestion or triggering antiperistalsis from the foregut in the process known as regurgitation or 'bubbling'.

l-arginine via nitric oxide is an inhibitory feedback modulator of Aplysia feeding

An increase in l-arginine hemolymph concentration acts as a postingestion signal inhibiting Aplysia feeding. At physiological concentrations (a 10-μM increase over background), the inhibitory effect of l-arginine is too weak to block feeding in hungry animals. However, a 10-μM increase in l-arginine concentration acts along with another inhibitory stimulus, the sustained presence of food odor, to inhibit feeding after a period of access to food. A physiological concentration of l-arginine also blocked the excitatory effect of a stimulus enhancing feeding, pheromones secreted by mating conspecifics. High concentrations of l-arginine (2.5 mM) alone also inhibited ad libitum feeding. l-arginine is the substrate from which nitric oxide synthase (NOS) produces nitric oxide (NO). Both an NO donor and a 10-μM increase in l-arginine inhibited biting in response to a weak food stimulus. Treatment with NOS inhibitors initiated food-finding and biting in the absence of food, indicating that food initiates feeding against a background of tonic nitrergic inhibition. Increased feeding in response to blocking NOS is accompanied by firing of the metacerebral (MCC) neuron, a monitor of food arousal. The excitatory effect on the MCC of blocking NOS is indirect. The data suggest that l-arginine acts by amplifying NO synthesis, which acts as a background stimulus inhibiting feeding. Background modulation of neural activity and behavior by NO may also be present in other systems, but such modulation may be difficult to identify because its effects are evident only in the context of additional stimuli modulating behavior.

Neurons controlling Aplysia feeding inhibit themselves by continuous NO production

BACKGROUND

Neural activity can be affected by nitric oxide (NO) produced by spiking neurons. Can neural activity also be affected by NO produced in neurons in the absence of spiking?

METHODOLOGY/PRINCIPAL FINDINGS

Applying an NO scavenger to quiescent Aplysia buccal ganglia initiated fictive feeding, indicating that NO production at rest inhibits feeding. The inhibition is in part via effects on neurons B31/B32, neurons initiating food consumption. Applying NO scavengers or nitric oxide synthase (NOS) blockers to B31/B32 neurons cultured in isolation caused inactive neurons to depolarize and fire, indicating that B31/B32 produce NO tonically without action potentials, and tonic NO production contributes to the B31/B32 resting potentials. Guanylyl cyclase blockers also caused depolarization and firing, indicating that the cGMP second messenger cascade, presumably activated by the tonic presence of NO, contributes to the B31/B32 resting potential. Blocking NO while voltage-clamping revealed an inward leak current, indicating that NO prevents this current from depolarizing the neuron. Blocking nitrergic transmission had no effect on a number of other cultured, isolated neurons. However, treatment with NO blockers did excite cerebral ganglion neuron C-PR, a command-like neuron initiating food-finding behavior, both in situ, and when the neuron was cultured in isolation, indicating that this neuron also inhibits itself by producing NO at rest.

CONCLUSION/SIGNIFICANCE

Self-inhibitory, tonic NO production is a novel mechanism for the modulation of neural activity. Localization of this mechanism to critical neurons in different ganglia controlling different aspects of a behavior provides a mechanism by which a humeral signal affecting background NO production, such as the NO precursor L-arginine, could control multiple aspects of the behavior.

Characterization of taurine as anti-obesity agent in C. elegans

Background

Taurine plays an important role in reducing physiological stress. Recent studies indicated that taurine may serve as an anti-obesity agent at the cellular level. This study characterizes taurine’s potential anti-obesity function in C. elegans, which have become a popular in vivo model for understanding the regulatory basis of lipid biosynthesis and deposition.

Methods

Two strains of C. elegans were raised on a normal or high-fat diet: N2 (normal) and RB1600, a mutant in tub-1 that serves as a tubby homologue and functions parallel to the 3-ketoacyl-CoA thiolase gene (kat-1) in regulating lipid accumulation. Taurine’s effect on lipid deposition was characterized according to assays of Sudan black B staining, triglyceride content measurement, food consumption, and mobility comparison.

Results

When N2 was treated with taurine after the culture in the high-fat media, the worms showed lower lipid accumulation in the assays of the Sudan black B staining and the triglyceride quantification. The anti-obesity effect was less evident in the experiment for RB1600. When the amount of taurine was increased for the high-fat-diet-treated N2 strain, fat deposition decreased and mobility increased in a dose-dependent manner. In the food consumption assays, taurine did not cause a significant change in food intake.

Conclusions

Taken together, these results strongly imply that taurine plays an important role in reducing fat deposition by modulating cellular pathways for lipid accumulation and stimulating mobility, but not the pathways for lipid biosynthesis and food intake.

Job switching in ants: Role of a kinase

Reproductive division of labor is a defining characteristic of eusociality in insect societies. The task of reproduction is performed by the fertile males and queens of the colony, while the non-fertile female worker caste performs all other tasks related to colony upkeep, foraging and nest defence. Division of labor, or polyethism, within the worker caste is organized such that specific tasks are performed by discrete groups of individuals. Ordinarily, workers of one group will not participate in the tasks of other groups making the groups of workers behaviorally distinct. In some eusocial species, this has led to the evolution of a remarkable diversity of subcaste morphologies within the worker caste, and a division of labor amongst the subcastes. This caste polyethism is best represented in many species of ants where a smaller-bodied minor subcaste typically performs foraging duties while larger individuals of the major subcaste are tasked with nest defence. Recent work suggests that polyethism in the worker caste is influenced by an evolutionarily conserved, yet diversely regulated, gene called foraging (for), which encodes a cGMP-dependent protein kinase (PKG). Additionally, flexibility in the activity of this enzyme allows for workers from one task group to assist the workers of other task groups in times of need during the colony's life.In a recent article, Lucas and Sokolowski1 report that PKG mediates behavioral flexibility in the minor and major worker subcastes of the ant Pheidole pallidula. By changing the task-specific stimulus (a mealworm to induce foraging or alien intruders to induce defensive behavior) or pharmacologically manipulating PKG activity, they are able to alter the behavior of both subcastes. They also show differences in the spatial localization of the FOR protein in minor and major brains. Furthermore, manipulation of ppfor activity levels in the brain alters the behavior of both P. pallidula subcastes. The foraging gene is thus emerging as a major player in regulating the flexibility of responses to environmental change.

The antidiuretic neurohormone RhoprCAPA-2 downregulates fluid transport across the anterior midgut in the blood-feeding insect Rhodnius prolixus

Osmotic balance in insects is regulated by the excretory system, consisting of Malpighian tubules and the gut under the control of diuretic and antidiuretic factors. Terrestrial insects must conserve water, and antidiuresis is the norm, only interrupted by brief diuretic periods. Surprisingly, little is known about antidiuresis in insects. Two antidiuretic strategies have been described. The first antidiuretic mechanism involves the reabsorption of fluid from the primary urine in the hindgut. More recently, a second antidiuretic strategy was reported, consisting of inhibition of primary urine formation by the Malpighian tubules. Recently, we isolated, characterized, and cloned the gene encoding for the antidiuretic neurohormone (the neuropeptide RhoprCAPA-2) acting on the Malpighian tubules of Rhodnius prolixus. Here we describe a third, novel mechanism central to the antidiuretic strategy of R. prolixus, the inhibition of ion and fluid transport across the anterior midgut by RhoprCAPA-2. Our results show that RhoprCAPA-2 (1 micromol/l) reduces serotonin-stimulated fluid transport from 83 +/- 11 to 12 +/- 12 nl/min and equivalent short-circuit current from 20 +/- 4 to 5 +/- 0.7 microA/cm(2) in diuretic hormone-stimulated anterior midgut. RhoprCAPA-2 appears to function independently of intracellular cGMP or Ca(2+) in the midgut. Thus, the antidiuretic neurohormone RhoprCAPA-2 has multiple target tissues, and we hypothesize that RhoprCAPA-2 functions to coordinate the transport activity of the anterior midgut and Malpighian tubules so that the rate of fluid transport into the haemolymph by the anterior midgut matches the transport rate of Malpighian tubules to maintain the volume and ion composition of haemolymph.

cGMP-dependent protein kinase as a modifier of behaviour

The importance of cGMP-dependent protein kinase (PKG) to the modulation of behavioural phenotypes has become increasingly clear in recent decades. The effects of PKG on behaviour have been studied in diverse taxa from perspectives as varied as ethology, evolution, genetics and neuropharmacology. The genetic variation of the Drosophila melanogaster gene, foraging (for), has provided a fertile model for examining natural variation in a single major gene influencing behaviour. Concurrent studies in other invertebrates and mammals suggest that PKG is an important signalling molecule with varied influences on behaviour and a large degree of pleiotropy and plasticity. Comparing these cross-taxa effects suggests that there are several potentially overlapping behavioural modalities in which PKG signalling acts to influence behaviours which include feeding, learning, stress and biological rhythms. More in-depth comparative analyses across taxa of the similarities and differences of the influence of PKG on behaviour may provide powerful mechanistic explications of the evolution of behaviour.

Neural and molecular dissection of a C. elegans sensory circuit that regulates fat and feeding

A major challenge in understanding energy balance is deciphering the neural and molecular circuits that govern behavioral, physiological, and metabolic responses of animals to fluctuating environmental conditions. The neurally expressed TGF-beta ligand DAF-7 functions as a gauge of environmental conditions to modulate energy balance in C. elegans. We show that daf-7 signaling regulates fat metabolism and feeding behavior through a compact neural circuit that allows for integration of multiple inputs and the flexibility for differential regulation of outputs. In daf-7 mutants, perception of depleting food resources causes fat accumulation despite reduced feeding rate. This fat accumulation is mediated, in part, through neural metabotropic glutamate signaling and upregulation of peripheral endogenous biosynthetic pathways that direct energetic resources into fat reservoirs. Thus, neural perception of adverse environmental conditions can promote fat accumulation without a concomitant increase in feeding rate.

Dietary regulation of hypodermal polyploidization in C. elegans

BACKGROUND

Dietary restriction (DR) results in increased longevity, reduced fecundity and reduced growth in many organisms. Though many studies have examined the effects of DR on longevity and fecundity, few have investigated the effects on growth.

RESULTS

Here we use Caenorhabditis elegans to determine the mechanisms that regulate growth under DR. We show that rather than a reduction in cell number, decreased growth in wild type C. elegans under DR is correlated with lower levels of hypodermal polyploidization. We also show that mutants lacking wild type sensory ciliated neurons are small, exhibit hypo-polyploidization and more importantly, when grown under DR, reduce their levels of endoreduplication to a lesser extent than wild type, suggesting that these neurons are required for the regulation of hypodermal polyploidization in response to DR. Similarly, we also show that the cGMP-dependent protein kinase EGL-4 and the SMA/MAB signalling pathway regulate polyploidization under DR.

CONCLUSION

We show C. elegans is capable of actively responding to food levels to regulate adult ploidy. We suggest this response is dependent on the SMA/MAB signalling pathway.

Mechanistic approaches to the study of evolution: the functional synthesis

An emerging synthesis of evolutionary biology and experimental molecular biology is providing much stronger and deeper inferences about the dynamics and mechanisms of evolution than were possible in the past. The new approach combines statistical analyses of gene sequences with manipulative molecular experiments to reveal how ancient mutations altered biochemical processes and produced novel phenotypes. This functional synthesis has set the stage for major advances in our understanding of fundamental questions in evolutionary biology. Here we describe this emerging approach, highlight important new insights that it has made possible, and suggest future directions for the field.

Exploratory behaviour in NO-dependent cyclase mutants of Drosophila shows defects in coincident neuronal signalling

Background

Drosophila flies explore the environment very efficiently in order to colonize it. They explore collectively, not individually, so that when a few land on a food spot, they attract the others by signs. This behaviour leads to aggregation of individuals and optimizes the screening of mates and egg-laying on the most favourable food spots.

Results

Flies perform cycles of exploration/aggregation depending on the resources of the environment. This behavioural ecology constitutes an excellent model for analyzing simultaneous processing of neurosensory information. We reasoned that the decision of flies to land somewhere in order to achieve aggregation is based on simultaneous integration of signals (visual, olfactory, acoustic) during their flight. On the basis of what flies do in nature, we designed laboratory tests to analyze the phenomenon of neuronal coincidence. We screened many mutants of genes involved in neuronal metabolism and the synaptic machinery.

Conclusion

Mutants of NO-dependent cyclase show a specifically-marked behaviour phenotype, but on the other hand they are associated with moderate biochemical defects. We show that these mutants present errors in integrative and/or coincident processing of signals, which are not reducible to the functions of the peripheral sensory cells.

Theforaging gene ofDrosophila melanogaster: Spatial-expression analysis and sucrose responsiveness

The ability to identify and respond to food is essential for survival, yet little is known about the neural substrates that regulate natural variation in food-related traits. The foraging (for) gene in Drosophila melanogaster encodes a cGMP-dependent protein kinase (PKG) and has been shown to function in food-related traits. To investigate the tissue distribution of FOR protein, we generated an antibody against a common region of the FOR isoforms. In the adult brain we localized FOR to neuronal clusters and projections including neurons that project to the central complex, a cluster within the dorsoposterior region of the brain hemispheres, a separate cluster medial to optic lobes and lateral to brain hemispheres, a broadly distributed frontal-brain cluster, axon bundles of the antennal nerve and of certain subesophageal-ganglion nerves, and the medulla optic lobe. These newly described tissue distribution patterns of FOR protein provide candidate neural clusters and brain regions for investigation of neural networks that govern foraging-related traits. To determine whether FOR has a behavioral function in neurons we expressed UAS-for in neurons using an elav-gal4 driver and measured the effect on adult sucrose responsiveness (SR), known to be higher in rovers than sitters, the two natural variants of foraging. We found that pan-neuronal expression of for caused an increase in the SR of sitters, demonstrating a neural function for PKG in this food-related behavior.

Sexual behavior: a seminal peptide stimulates appetites

A new study shows that female fruitflies eat more after mating, and that a multi-functional peptide provided in the seminal fluid of their mates induces this behavior. These findings contribute significantly to our understanding of mating behaviors and resource allocation, and may provide insights useful for controlling the reproduction of insect pests.