From behavior to fictive feeding: anatomy, innervation and activation pattern of pharyngeal muscles of Calliphora vicina 3rd instar larvae

Bolwig Organ and Its Role in the Photoperiodic Response of Sarcophaga similis Larvae

Flesh-fly Sarcophaga similis larvae exhibit a photoperiodic response, in which short days induce pupal diapause for seasonal adaptation. Although the spectral sensitivity of photoperiodic photoreception is known, the photoreceptor organ remains unclear. We morphologically identified the Bolwig organ, a larval-photoreceptor identified in several other fly species, and examined the effects of its removal on the photoperiodic response in S. similis. Backfill-staining and embryonic-lethal-abnormal-vision (ELAV) immunohistochemical-staining identified ~34 and 38 cells, respectively, in a spherical body at the ocular depression of the cephalopharyngeal skeleton, suggesting that the spherical body is the Bolwig organ in S. similis. Forward-fill and immunohistochemistry revealed that Bolwig-organ neurons terminate in the vicinity of the dendritic fibres of pigment-dispersing factor-immunoreactive and potential circadian-clock neurons in the brain. After surgical removal of the Bolwig-organ regions, diapause incidence was not significantly different between short and long days, and was similar to that in the insects with an intact organ, under constant darkness. However, diapause incidence was not significantly different between the control and Bolwig-organ-removed insects for each photoperiod. These results suggest that the Bolwig organ contributes partially to photoperiodic photoreception, and that other photoreceptors may also be involved.

Manduca Contactin Regulates Amyloid Precursor Protein-Dependent Neuronal Migration

Amyloid precursor protein (APP) was originally identified as the source of β-amyloid peptides that accumulate in Alzheimer's disease (AD), but it also has been implicated in the control of multiple aspects of neuronal motility. APP belongs to an evolutionarily conserved family of transmembrane proteins that can interact with a variety of adapter and signaling molecules. Recently, we showed that both APP and its insect ortholog [APPL (APP-Like)] directly bind the heterotrimeric G-protein Goα, supporting the model that APP can function as an unconventional Goα-coupled receptor. We also adapted a well characterized assay of neuronal migration in the hawkmoth, Manduca sexta, to show that APPL-Goα signaling restricts ectopic growth within the developing nervous system, analogous to the role postulated for APP family proteins in controlling migration within the mammalian cortex. Using this assay, we have now identified Manduca Contactin (MsContactin) as an endogenous ligand for APPL, consistent with previous work showing that Contactins interact with APP family proteins in other systems. Using antisense-based knockdown protocols and fusion proteins targeting both proteins, we have shown that MsContactin is selectively expressed by glial cells that ensheath the migratory neurons (expressing APPL), and that MsContactin-APPL interactions normally prevent inappropriate migration and outgrowth. These results provide new evidence that Contactins can function as authentic ligands for APP family proteins that regulate APP-dependent responses in the developing nervous system. They also support the model that misregulated Contactin-APP interactions might provoke aberrant activation of Goα and its effectors, thereby contributing to the neurodegenerative sequelae that typify AD.

SIGNIFICANCE STATEMENT

Members of the amyloid precursor protein (APP) family participate in many aspects of neuronal development, but the ligands that normally activate APP signaling have remained controversial. This research provides new evidence that members of the Contactin family function as authentic ligands for APP and its orthologs, and that this evolutionarily conserved class of membrane-attached proteins regulates key aspects of APP-dependent migration and outgrowth in the embryonic nervous system. By defining the normal role of Contactin-APP signaling during development, these studies also provide the framework for investigating how the misregulation of Contactin-APP interactions might contribute to neuronal dysfunction in the context of both normal aging and neurodegenerative conditions, including Alzheimer's disease.

Synaptic transmission parallels neuromodulation in a central food-intake circuit

NeuromedinU is a potent regulator of food intake and activity in mammals. In Drosophila, neurons producing the homologous neuropeptide hugin regulate feeding and locomotion in a similar manner. Here, we use EM-based reconstruction to generate the entire connectome of hugin-producing neurons in the Drosophila larval CNS. We demonstrate that hugin neurons use synaptic transmission in addition to peptidergic neuromodulation and identify acetylcholine as a key transmitter. Hugin neuropeptide and acetylcholine are both necessary for the regulatory effect on feeding. We further show that subtypes of hugin neurons connect chemosensory to endocrine system by combinations of synaptic and peptide-receptor connections. Targets include endocrine neurons producing DH44, a CRH-like peptide, and insulin-like peptides. Homologs of these peptides are likewise downstream of neuromedinU, revealing striking parallels in flies and mammals. We propose that hugin neurons are part of an ancient physiological control system that has been conserved at functional and molecular level.

DOI:http://dx.doi.org/10.7554/eLife.16799.001

Localization of Motor Neurons and Central Pattern Generators for Motor Patterns Underlying Feeding Behavior in Drosophila Larvae

Motor systems can be functionally organized into effector organs (muscles and glands), the motor neurons, central pattern generators (CPG) and higher control centers of the brain. Using genetic and electrophysiological methods, we have begun to deconstruct the motor system driving Drosophila larval feeding behavior into its component parts. In this paper, we identify distinct clusters of motor neurons that execute head tilting, mouth hook movements, and pharyngeal pumping during larval feeding. This basic anatomical scaffold enabled the use of calcium-imaging to monitor the neural activity of motor neurons within the central nervous system (CNS) that drive food intake. Simultaneous nerve- and muscle-recordings demonstrate that the motor neurons innervate the cibarial dilator musculature (CDM) ipsi- and contra-laterally. By classical lesion experiments we localize a set of CPGs generating the neuronal pattern underlying feeding movements to the subesophageal zone (SEZ). Lesioning of higher brain centers decelerated all feeding-related motor patterns, whereas lesioning of ventral nerve cord (VNC) only affected the motor rhythm underlying pharyngeal pumping. These findings provide a basis for progressing upstream of the motor neurons to identify higher regulatory components of the feeding motor system.

Identification of motor neurons and a mechanosensitive sensory neuron in the defecation circuitry of Drosophila larvae

Defecation allows the body to eliminate waste, an essential step in food processing for animal survival. In contrast to the extensive studies of feeding, its obligate counterpart, defecation, has received much less attention until recently. In this study, we report our characterizations of the defecation behavior of Drosophila larvae and its neural basis. Drosophila larvae display defecation cycles of stereotypic frequency, involving sequential contraction of hindgut and anal sphincter. The defecation behavior requires two groups of motor neurons that innervate hindgut and anal sphincter, respectively, and can excite gut muscles directly. These two groups of motor neurons fire sequentially with the same periodicity as the defecation behavior, as revealed by in vivo Ca(2+) imaging. Moreover, we identified a single mechanosensitive sensory neuron that innervates the anal slit and senses the opening of the intestine terminus. This anus sensory neuron relies on the TRP channel NOMPC but not on INACTIVE, NANCHUNG, or PIEZO for mechanotransduction.

A new kind of auxiliary heart in insects: functional morphology and neuronal control of the accessory pulsatile organs of the cricket ovipositor

Introduction

In insects, the pumping of the dorsal heart causes circulation of hemolymph throughout the central body cavity, but not within the interior of long body appendages. Hemolymph exchange in these dead-end structures is accomplished by special flow-guiding structures and/or autonomous pulsatile organs (“auxiliary hearts”). In this paper accessory pulsatile organs for an insect ovipositor are described for the first time. We studied these organs in females of the cricket Acheta domesticus by analyzing their functional morphology, neuroanatomy and physiological control.

Results

The lumen of the four long ovipositor valves is subdivided by longitudinal septa of connective tissue into efferent and afferent hemolymph sinuses which are confluent distally. The countercurrent flow in these sinuses is effected by pulsatile organs which are located at the bases of the ovipositor valves. Each of the four organs consists of a pumping chamber which is compressed by rhythmically contracting muscles. The morphology of the paired organs is laterally mirrored, and there are differences in some details between the dorsal and ventral organs. The compression of the pumping chambers of each valve pair occurs with a left-right alternating rhythm with a frequency of 0.2 to 0.5 Hz and is synchronized between the dorsal and ventral organs. The more anteriorly located genital chamber shows rhythmical lateral movements simultaneous to those of the ovipositor pulsatile organs and probably supports the hemolymph exchange in the abdominal apex region. The left-right alternating rhythm is produced by a central pattern generator located in the terminal ganglion. It requires no sensory feedback for its output since it persists in the completely isolated ganglion. Rhythm-modulating and rhythm-resetting interneurons are identified in the terminal ganglion.

Conclusion

The circulatory organs of the cricket ovipositor have a unique functional morphology. The pumping apparatus at the base of each ovipositor valve operates like a bellow. It forces hemolymph via sinuses delimited by thin septa of connective tissue in a countercurrent flow through the valve lumen. The pumping activity is based on neurogenic control by a central pattern generator in the terminal ganglion.

Discontinuous foraging behavior of necrophagous Lucilia sericata (Meigen 1826) (Diptera Calliphoridae) larvae

Larvae of the necrophagous Blowfly Lucilia sericata (Diptera Calliphoridae) live on vertebrate cadavers. Although continuously feeding was previously assumed for this species, we hypothesized that larvae do not feed constantly. According to this hypothesis, their crop should not always be full, which should be reflected in crop surfaces. We dissected and measured the crops of larvae of the same age and bred in the same conditions. Crop surfaces of 117 larvae just removed from the food ranged from 0 to 16.6 mm(2) (mean=5.325±2.84 mm(2)). The distribution of these crop surfaces indicates a continuous variation of satiation/feeding activity in the population. Starving experiments showed a quite long digestive process. After 90 min of starving, the decrease in crop surfaces became obvious, but 150 min were necessary to observe more than a half of the population with an empty crop (less than 2 mm(2)). No more differences were observed after 150, 180 and 240 min of starving. We finally used starved larvae to observe the kinetic of food absorption and the duration of the food-intake phase. Our results indicates that larvae can ingest faster than they digest. After 5 min spent in the food, 70% of the larvae had a crop surface larger or equal to 8 mm(2). We observed for the first time an over-feeding of the larvae, with high crop surfaces overrepresented compared to larvae never starved (control). Together, these results indicate that larvae do not feed continuously, and regulate their foraging behavior. We propose that the foraging behavior of the larvae creates a permanent movement inside the larval masses. This turnover/scramble competition may be linked to the larval-mass effect, i.e. the local temperature increase observed in large necrophagous larvae aggregates.

The skeletomuscular system of the larva of Drosophila melanogaster (Drosophilidae, Diptera): a contribution to the morphology of a model organism

The morphological features of the third instar larva of the most important insect model, Drosophila melanogaster, are documented for the first time using a broad spectrum of modern morphological techniques. External structures of the body wall, the cephaloskeleton, and the musculature are described and illustrated. Additional information about other internal organs is provided. The systematic implications of the findings are discussed briefly. Internal apomorphic features of Brachycera and Cyclorrhapha are confirmed for Drosophila. Despite the intensive investigations of the phylogeny of the megadiverse Diptera, evolutionary reconstructions are still impeded by the scarcity of anatomical data for brachyceran larvae. The available morphological information for the life stages of three insect model organisms -D. melanogaster (Diptera, Drosophilidae), Manduca sexta (Lepidoptera, Sphingidae) and Tribolium castaneum (Coleoptera, Tenebrionidae) - is addressed briefly. The usefulness of a combination of traditional and innovative techniques for an optimized acquisition of anatomical data for different life stages is highlighted.

Epithelial homeostasis and the underlying molecular mechanisms in the gut of the insect model Drosophila melanogaster

Insects mostly develop on decaying and contaminated organic matter and often serve as vectors of biologically transmitted diseases by transporting microorganisms to the plant and animal hosts. As such, insects are constantly ingesting microorganisms, a small fraction of which reach their epithelial surfaces, mainly their digestive tract, where they can establish relationships ranging from symbiosis to mutualism or even parasitism. Understanding the tight physical, genetic, and biochemical interactions that takes place between intestinal epithelia and either resident or infectious microbes has been a long-lasting objective of the immunologist. Research in this field has recently been re-vitalized with the development of deep sequencing techniques, which allow qualitative and quantitative characterization of gut microbiota. Interestingly, the recent identification of regenerative stem cells in the Drosophila gut together with the initial characterization of Drosophila gut microbiota have opened up new avenues of study aimed at understanding the mechanisms that regulate the dialog between the Drosophila gut epithelium and its microbiota of this insect model. The fact that some of the responses are conserved across species combined with the power of Drosophila genetics could make this organism model a useful tool to further elucidate some aspects of the interaction occurring between the microbiota and the human gut.

Immunohistological localization of serotonin in the CNS and feeding system of the stable fly Stomoxys calcitrans L. (Diptera: Muscidae)

Serotonin, or 5-hydroxytryptamine (5-HT), plays critical roles as a neurotransmitter and neuromodulator that control or modulate many behaviors in insects, such as feeding. Neurons immunoreactive (IR) to 5-HT were detected in the central nervous system (CNS) of the larval and adult stages of the stable fly, Stomoxys calcitrans, using an immunohistological technique. The location and pattern of the 5-HT IR neurons are described and compared for these two different developmental stages. Anatomical features of the fly feeding system were analyzed in third instar larvae and adult flies using a combination of histological and immunohistological techniques. In third instar larvae, the cibarial dilator muscles were observed within the cibarial pump skeleton and innervated by 5-HT IR neurons in nerves arising from the brain. There were four pairs of nerves arising from the frontal surface of the larval brain that innervate the cibarial pump muscles, pharynx, and muscles controlling the mouth hooks. A strong serotoninergic innervation of the anterior stomatogastric system was observed, which suggests 5-HT may play a role in the coordination of different phases of food ingestion by larvae. Similarly, many 5-HT IR neurons were found in both the brain and the thoracico-abdominal ganglia in the adult, some of which innervate the cibarial pump dilator muscles and the stomatogastric muscles. This is tnhe first report describing neuromuscular structures of the stable fly feeding system. The results reported here suggest 5-HT may play a critical role in feeding behaviors of stable fly larvae and adults.

Gustatory feedback affects feeding related motor pattern generation in starved 3rd instar larvae of Calliphora vicina

Gustatory feedback allows animals to distinguish between edible and noxious food and adapts centrally generated feeding motor patterns to environmental demands. In reduced preparations obtained from starved Calliphora larvae, putatively appetitive (ethanol), aversive (sodium acetate) and neutral (glucose) gustatory stimuli were applied to the anterior sense organs. The resulting sensory response was recorded from the maxillary and antennal nerves. All three stimuli increased the neural activity in both nerves. Recordings obtained from the antennal nerve to monitor the activation pattern of the cibarial dilator muscles, demonstrated an effect of gustatory input on the central pattern generator for feeding. Ethanol consistently enhanced the rhythmic activity of the CDM motor neurons either by speeding up the rhythm or by increasing the burst duration. Ethanol also had an enhancing effect on the motor patterns of a protractor muscle which moves the cephalopharyngeal skeleton relative to the body. Sodium acetate showed a state dependent effect: in preparations without spontaneous CDM activity it initiated rhythmic motor patterns, while an ongoing CDM rhythm was inhibited. Surprisingly glucose had an enhancing effect which was less pronounced than that of ethanol. Gustatory feedback therefore can modify and adapt the motor output of the multifunctional central pattern generator for feeding.

Feel the heat: The effect of temperature on development, behavior and central pattern generation in 3rd instar Calliphora vicina larvae

Like in all poikilothermic animals, higher temperatures increase developmental rate and activity in Calliphora vicina larvae. We therefore could expect temperature to have a persistent effect on the output of the feeding and crawling central pattern generators (CPGs). When confronted with a steep temperature gradient, larvae show evasive behavior after touching the substrate with the cephalic sense organs. Beside this reflex behavior the terminal- and dorsal organ might also mediate long term CPG modulation. Both organs were thermally stimulated while their response was recorded from the maxillary- or antennal nerve. The terminal organ showed a tonic response characteristic while the dorsal organ was not sensitive to temperature. Thermal stimulation of the terminal organ did not affect the ongoing patterns of fictive feeding or crawling, recorded from the antennal- or abdominal nerve respectively. A selective increase of the central nervous system (CNS) temperature accelerated the motor patterns of both feeding and crawling. We propose that temperature affects centrally generated behavior via two pathways: short term changes like thermotaxis are mediated by the terminal organ, while long term adaptations like increased feeding rate are caused by temperature sensitive neurons in the CNS which were recently shown to exist in Drosophila larvae.

See the light: electrophysiological characterization of the Bolwig organ's light response of Calliphora vicina 3rd instar larvae

The anatomy and development of the larval cyclorraphous Diptera visual system is well established. It consists of the internal Bolwig organ (BO), and the associated nerve connecting it to the brain. The BO contributes to various larval behaviors but was never electrophysiologically characterized. We recorded extracellulary from the Bolwig nerve of 3rd instar Calliphora vicina larvae to quantify the sensory response caused by BO stimulation with light stimuli of different wavelengths, intensities and directions. Consistent with previous behavioral experiments we found the BO most sensitive to white and green, followed by blue, yellow, violet and red light. The BO showed a phasic-tonic response curve. Increasing light intensity produced a sigmoid response curve with an approximate threshold of 0.0105 nW/cm(2) and a dynamic range from 0.105 nW/cm(2) to 52.5 nW/cm(2). No differences exist between feeding and wandering larvae which display opposed phototaxis. This excludes reduced BO sensitivity from causing the switch in behavior. Correlating to the morphology of the BO frontal light evoked the maximal reaction, while lateral light reduced the neural response asymmetrically: Light applied ipsilaterally to the recorded BO always produced a stronger response than when applied from the contralateral side. This implies that phototacic behavior is based on a tropotactic mechanism.

The cephalic and pharyngeal sense organs of Calliphora vicina 3rd instar larvae are mechanosensitive but have no profound effect on ongoing feeding related motor patterns

The anterior segments of cyclorraphous Diptera larvae bear various sense organs: the dorsal- and terminal organ located on the cephalic lobes, the ventral- and labial organs associated with the mouthplate and the internal labral organ which lies on the dorsal surface of the esophagus. The sense organs are connected to the brain via the antennal nerve (dorsal- and labral organ) or the maxillary nerve (terminal-, ventral-, labial organ). Although their ultrastructure suggests also a mechanosensory function only their response to olfactory and gustatory stimuli has been investigated electrophysiologically. Here we stimulated the individual organs with step-, ramp-, and sinusoidal stimuli of different amplitude while extracellulary recording their afferents from the respective nerves. The external organs show a threshold of approximately 2 microm. All organs responded phasically and did not habituate to repetitive stimuli. The low threshold of the external organs combined with their rhythmically exposure to the substrate suggested a putative role in the temporal coordination of feeding. We therefore repetitively stimulated individual organs while simultaneously monitoring the centrally generated motor pattern for food ingestion. Neither the dorsal-, terminal- or ventral organ afferents had an obvious effect on the ongoing motor rhythm. Various reasons explaining these results are discussed.

Peristalsis in the junction region of the Drosophila larval midgut is modulated by DH31 expressing enteroendocrine cells

Background

The underlying cellular and molecular mechanisms that coordinate the physiological processes in digestion are complex, cryptic, and involve the integration of multiple cellular and organ systems. In all intestines, peristaltic action of the gut moves food through the various stages of digestion from the anterior end towards the posterior, with the rate of flow dependent on signals, both intrinsic and extrinsic to the gut itself.

Results

We have identified an enteroendocrine cell type that regulates gut motility in the Drosophila melanogaster larval midgut. These cells are located at the junction of the anterior and the acidic portions of the midgut and are a group of enteroendocrine cells that express the peptide hormone Diuretic Hormone 31 in this region of the gut. Using cell ablation and ectopic activation via expression of the Chlamydomonas reinhardtii blue light-activated channelopsin, we demonstrate that these enteroendocrine cells are both necessary and sufficient for the peristalsis in the junction region of the midgut and require the Diuretic Hormone 31 to affect normal peristalsis in this region. Within the same junction region of the midgut, we have also identified morphological features suggesting that this region acts as a valve that regulates the transit of food from the anterior midgut into the acidic portion of the gut.

Conclusions

We have characterized and described a set of enteroendocrine cells called the Midgut Junction DH31 expressing cells that are required for peristaltic movement in the junction region between the anterior portion and acidic region of the larval midgut of Drosophila melanogaster. We have shown that the Midgut Junction DH31 expressing cells are necessary and sufficient for motility and that the peptide hormone DH31 is required for peristalsis in the junction region of the midgut. The Drosophila model system will allow for a further dissection of the digestion process and provide a better understanding of the mechanisms that regulate digestion in all organisms.

The thoracic muscular system and its innervation in third instar Calliphora vicina Larvae. I. Muscles of the pro- and mesothorax and the pharyngeal complex

An anatomical description is given by the muscles in the pro- and mesothorax, and those associated with the feeding apparatus (cephalopharyngeal skeleton, CPS) that participate in feeding behavior in third instar Calliphora larvae. The body wall muscles in the pro- and mesothoracic segments are organized in three layers: internal, intermedial, and external. The muscles were labeled with roman numerals according to the nomenclature in use for the abdominal segments. Muscles associated with the CPS are labeled according to their function. The prothorax bears five pairs of lateral symmetrically longitudinal segmental body wall muscles and lacks the transversal muscle group present in the mesothorax and abdominal segments. Additionally, four pairs of intersegmental muscles project from the prothorax to the second, fourth, and fifth segment. The mesothorax bears 15 pairs of segmental longitudinal and 18 pairs of transversal muscles. The accessory pharyngeal muscles span the CPS and the cuticle. Three pairs of protractors and retractors and two pairs of mouth hook accessors (MH(AC)) exist, which move the CPS relative to the body. The pharyngeal muscles are exclusively attached to the structures of the CPS. The mouth hook elevators and depressors, which mediate the hooks rotation are attached to the ventral arm of the CPS and project to a dorsal (elevators) or ventral (depressors) protuberance of the mouth hooks. The cibarial dilator muscles (CDM) span the dorsal arms of the CPS and the dorsal surface of the esophagus and mediate food ingestion. The labial retractors (LRs) lack antagonists and project from the ventral surface of the CPS to the unpaired labium. Contractions of these muscles open the mouth cavity.

The thoracic muscular system and its innervation in third instar Calliphora vicina Larvae. II. Projection patterns of the nerves associated with the pro- and mesothorax and the pharyngeal complex

We describe the anatomy of the nerves that project from the central nervous system (CNS) to the pro- and mesothoracic segments and the cephalopharyngeal skeleton (CPS) for third instar Calliphora larvae. Due to the complex branching pattern we introduce a nomenclature that labels side branches of first and second order. Two fine nerves that were not yet described are briefly introduced. One paired nerve projects to the ventral arms (VAs) of the CPS. The second, an unpaired nerve, projects to the ventral surface of the cibarial part of the esophagus (ES). Both nerves were tentatively labeled after the structures they innervate. The antennal nerve (AN) innervates the olfactory dorsal organ (DO). It contains motor pathways that project through the frontal connectives (FC) to the frontal nerve (FN) and innervate the cibarial dilator muscles (CDM) which mediate food ingestion. The maxillary nerve (MN) innervates the sensory terminal organ (TO), ventral organ (VO), and labial organ (LO) and comprises the motor pathways to the mouth hook (MH) elevator, MH depressor, and the labial retractor (LR) which opens the mouth cavity. An anastomosis of unknown function exists between the AN and MN. The prothoracic accessory nerve (PaN) innervates a dorsal protractor muscle of the CPS and sends side branches to the aorta and the bolwig organ (BO) (stemmata). In its further course, this nerve merges with the prothoracic nerve (PN). The architecture of the PN is extremely complex. It innervates a set of accessory pharyngeal muscles attached to the CPS and the body wall musculature of the prothorax. Several anastomoses exist between side branches of this nerve which were shown to contain motor pathways. The mesothoracic nerve (MeN) innervates a MH accessor and the longitudinal and transversal body wall muscles of the second segment.

The brain can eat: establishing the existence of a central pattern generator for feeding in third instar larvae of Drosophila virilis and Drosophila melanogaster

To establish the existence of a central pattern generator for feeding in the larval central nervous system of two Drosophila species, the gross anatomy of feeding related muscles and their innervation is described, the motor units of the muscles identified and rhythmic motor output recorded from the isolated CNS. The cibarial dilator muscles that mediate food ingestion are innervated by the frontal nerve. Their motor pathway projects from the brain through the antennal nerves, the frontal connectives and the frontal nerve junction. The mouth hook elevator and depressor system is innervated by side branches of the maxillary nerve. The motor units of the two muscle groups differ in amplitude: the elevator is always activated by a small unit, the depressor by a large one. The dorsal protractors span the cephalopharyngeal skeleton and the body wall hence mediating an extension of the CPS. These muscles are innervated by the prothoracic accessory nerve. Rhythmic motor output produced by the isolated central nervous system can simultaneously be recorded from all three nerves. The temporal pattern of the identified motor units resembles the sequence of muscle contractions deduced from natural feeding behavior and is therefore considered as fictive feeding. Phase diagrams show an almost identical fictive feeding pattern is in both species.