Timing of Environmental Enrichment Affects Memory in the House Cricket,Acheta domesticus

Learning appears to be ubiquitous among animals, as it plays a key role in many behaviors including foraging and reproduction. Although there is some genetic basis for differences in learning ability and memory retention, environment also plays an important role, as it does for any other trait. For example, adult animals maintained in enriched housing conditions learn faster and remember tasks for longer than animals maintained in impoverished conditions. Such plasticity in adult learning ability has often been linked to plasticity in the brain, and studies aimed at understanding the mechanisms, stimuli, and consequences of adult behavioral and brain plasticity are numerous. However, the role of experiences during post-embryonic development in shaping plasticity in adult learning ability and memory retention remain relatively unexplored. Using the house cricket (Acheta domesticus) as a model organism, we developed a protocol to allow the odor preference of a large number of crickets to be tested in a short period of time. We then used this new protocol to examine how enrichment or impoverishment at two developmental stages (either the last nymphal instar or young adult) affected adult memory. Our results show that regardless of nymphal rearing conditions, crickets that experienced an enriched rearing condition as young adults performed better on a memory task than individuals that experienced an impoverished condition. Older adult crickets (more than 1 week post adult molt) did not demonstrate differences in memory of the odor task, regardless of rearing condition as a young adult. Our results suggest that environmentally-induced plasticity in memory may be restricted to the young adult stage.     

Sperm Penetration and in vitro Fertilization of the Egg of the House Cricket Acheta domesticus

Summary

A study of sperm penetration of the egg of the house cricket, Acheta domesticus, using a fluorescent microscope technique, showed that sperm penetration of the chorion, prior to fertilization, is not restricted to a specialised area of the egg surface, such as the micropyle. An acrosomal filament is seen on penetrating sperm. Polyspermy (multiple sperm attachment) is seen under normal conditions.

Eggs fertilized in vitro developed to the 4 day (pre-katatrepsis) stage, but did not undergo katatrepsis. Development was confirmed by cytogenetic studies. The percentage of eggs showing cleavage nuclei (i.e. initial development) was 59% after in vitro fertilization and 5% in ovarian eggs incubated in a hypotonic medium.     

Muscarinic and Nicotinic Cholinergic Binding Sites in the Terminal Abdominal Ganglion of the Cricket (Acheta domesticus)

Cricket (Acheta domesticus) terminal abdominal ganglia (TG) contain high concentrations (approximately 2 pmol/mg protein) of muscarinic and nicotinic cholinergic binding sites, based on the capacity of TG to bind specifically the labelled ligands L-[3H]quinuclidinyl benzilate ([3H]QNB) and [125I]alpha-bungarotoxin ([125I]alpha-BGT) with high affinity. For both ligands, binding is saturable and reversible. Competitive displacement experiments indicate that the [3H]QNB and [125I]alpha-BGT binding sites probably represent pharmacologically distinct classes of putative TG acetylcholine receptors (AChRs). Results from physiological recording and autoradiographic localization experiments demonstrate that a portion of the putative nicotinic AChRs is localized in synaptic regions of the well-characterized cercal sensory-giant interneuron pathway in the TG, where they are likely to serve as functional synaptic AChRs. Unlike nicotinic ligands, muscarinic agents do not appear to be pharmacologically active in this pathway. Therefore, in the insect CNS, putative muscarinic and nicotinic AChRs coexist at high density, but can be pharmacologically distinguished from one another on the basis of criteria derived from both ligand binding and physiological methods.     

Susceptibility of North-American and European crickets to Acheta domesticus densovirus (AdDNV) and associated epizootics

The European house cricket, Acheta domesticus L., is highly susceptible to A. domesticus densovirus (AdDNV). Commercial rearings of crickets in Europe are frequently decimated by this pathogen. Mortality was predominant in the last larval stage and young adults. Infected A. domesticus were smaller, less active, did not jump as high, and the adult females seldom lived more than 10-14 days. The most obvious pathological change was the completely empty digestive caecae. Infected tissues included adipose tissue, midgut, epidermis, and Malpighian tubules. Sudden AdDNV epizootics have decimated commercial mass rearings in widely separated parts of North America since the autumn of 2009. Facilities that are producing disease-free crickets have avoided the importation of crickets and other non-cricket species (or nonliving material). Five isolates from different areas in North America contained identical sequences as did AdDNV present in non-cricket species collected from these facilities. The North American AdDNVs differed slightly from sequences of European AdDNV isolates obtained in 1977, 2004, 2006, 2007 and 2009 and an American isolate from 1988. The substitution rate of the 1977 AdDNV 5 kb genome was about two nucleotides per year, about half of the substitutions being synonymous. The American and European AdDNV strains are estimated to have diverged in 2006. The lepidopterans Spodoptera littoralis and Galleria mellonella could not be infected with AdDNV. The Jamaican cricket, Gryllus assimilis, and the European field cricket, Gryllus bimaculatus, were also found to be resistant to AdDNV.     

The Scent of Danger: the Impact of Predator Chemical Cues on Emergence from Refuge and Willingness to Autotomize Limbs in the House Cricket (<Emphasis Type="Italic">Acheta domesticus</Emphasis>)

Prey can accurately assess predation risk via the detection of chemical cues and take appropriate measures to survive encounters with predators. Research on the chemical ecology of terrestrial invertebrate predator-prey interactions has repeatedly found that direct chemical cues can alter prey organisms’ antipredator behavior. However, much of this research has focused on the chemical mediation of avoidance and immobility by cues from lycosid spiders neglecting other prominent invertebrate predators and behavior such as autotomy. In our study, house crickets (Acheta domesticus) were exposed to cues from cricket-fed orange-footed centipedes (Cormocephalus aurantiipes), red-back spiders (Latrodectus hasselti), an odorous (cologne) control, and a non-odorous control to determine whether direct chemical cues had any influence on two types of anti-predatory behavior: the willingness (latency) to emerge from a refuge and to autotomize limbs. Exposure to C. aurantiipes cues resulted in a significantly slower emergence from a refuge, but exposure to L. hasselti cues did not. Direct chemical cues had no influence on initial autotomy, but exposure to L. hasselti cues did significantly decrease the latency to autotomize a second limb. That cues from L. hasselti had an influence on a second autotomy, but not initial autotomy may be because crickets that undergo autotomy for a second time may perceive themselves to be already at a higher risk of predation as they were already missing a limb. Variation in responses to cues from different predators demonstrates a need to examine the influence of chemical cues from a wider variety of invertebrate predators on anti-predator behavior.     

Temperature and the energetics of development in the house cricket (Acheta domesticus)

The influence of rearing temperature on the energetics of development was investigated in house crickets (Acheta domesticus). Crickets raised at 25 degrees C grew slower (0.51 mg d(-1), dry mass basis) and took longer to develop (119 d) but obtained a greater adult body mass (61 mg, dry mass) than crickets reared at 28 degrees C (0.99 mg d(-1), 49 d, 48 mg). Total metabolic energy consumed during development at 25 degrees C (1351 J) was twice that at 28 degrees C (580 J) primarily because of the longer development period, and as a consequence the specific net cost of growth was much greater for crickets reared at 25 degrees C (22.1 kJ g(-1)) than 28 degrees C (11.9 kJ g(-1)).     

The stimulation of territorial singing in house crickets (Acheta domesticus)

Summary The chirp rate in a territorial male cricket can be increased by playing chirps from a tape recorder. The increase is independent of the cricket's chirp rate before stimulation as long as the highest possible chirp rates are not yet reached (Figs. 5, 6, 8), but the size of the increase depends on the chirp rate of the stimulus used. After the end of stimulation the chirp rate returns exponentially to its previous level with a half Me of about 20 seconds.A momentarily silent cricket is more likely to start chirping at the beginning of stimulation and less so after a few minutes of stimulation than would be expected without stimulation. The chirp rate reached in these cases is higher the sooner the cricket starts chirping during stimulation (Figs. 9, 10, 11). These regularities can easily be deduced by allowing the chirp activity to have negative values if no chirps occur (see discussion).

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Zusammenfassung Spielt man einem zirpenden territorialen Heimchen das Zirpen eines Artgenossen vor, so kann sich seine Zirp-Rate steigern. Solange höchst mögliche Zirp-Raten noch nicht erreicht sind, ist dieser Zuwachs unabhängig von der Zirp-Rate vor dem Vorspielen. Der Betrag dieses Zuwachses hängt aber von der Zirp-Rate des verwendeten Reizgesanges ab. Nach Ende des Vorspielens dieses Gesanges kehrt die Zirp-Rate des Heimchens exponentiell mit einer Halbwertzeit von etwa 20 sec auf ihr früheres Niveau zurück.Ein momentan schweigendes Heimchen beginnt mit größerer Wahrscheinlichkeit zu Beginn des Reizgesanges und mit geringerer Wahrscheinlichkeit zu späteren Zeitpunkten zu zirpen, als man ohne Vorspiel des Reizgesanges erwartet. In diesen Fällen erreicht die Zirp-Rate höhere Werte, je früher das Heimchen zu zirpen beginnt. Diese Zusammenhänge lassen sich leicht herleiten, wenn man negative Werte für die Zirpaktivität zuläßt, wenn das Zirpen selbst nicht auftritt.

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The Deutsche Forschungsgemeinschaft loaned part of the electronic apparatus used in these studies and the Volkswagen-Stiftung granted funds for further electronic equipment.     

Interactions between social factors and ovarian development in the European house cricket Acheta domesticus

Several endocrine-mediated processes in insects are influenced by environmental factors including the density and sex ratio of populations. Effects of grouping on total egg production and rate of vitellogenic ovary development were assessed in virgin Acheta domesticus (L.). Females midway through their last nymphal instar were isolated from a stock population of adults and nymphs of both sexes and maintained in groups or as isolates at 26–27°C, 70% relative humidity, on a 12L-12D photoperiod. The number of fully grown oocytes produced during the first 18 days of adult life was lower for animals in groups of 10 or 15 than for isolates, but antennectomy abolished this group effect. By contrast, terminal and penultimate oocyte length and ovary dry weight were greater in 5-day-old - pairs than in isolates. The presence of mature males during the first 21 days of adult life did not affect total egg production. Whether these group effects on cricket ovary development are mediated by the endocrine system is not yet known.

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Interaction entre les facteurs sociaux et le développement ovarien d'Acheta domesticus

Résumé L'étude a examiné les effets de groupement sur la production d'oeufs et sur la vitesse de la vitellogenèse chez les femelles vierges d'Acheta domesticus. Des femelles à la moitié de leur dernier stade larvaire, isolées d'une population adulte de base, et des nymphes des deux sexes ont été conservées en groupes ou isolées dans des récipients en plastique de 150 mm de diamètre et de 25 mm de hauteur à 26–27°C, 70% d'humidité relative et avec une photopériode de 12/12. La production totale des oeufs mûrs formés pendant les 18 premiers jours de vie imaginale était plus faible pour les animaux en groupes de 10 ou 15 que pour ceux qui étaient isolés, mais l'antennotectomie a éliminé cet effet de groupe. Au contraire, la longueur des derniers et avant-derniers ovocytes et le poids sec des ovaires étaient supérieurs pour les paires de 2 femelles de 5 jours que chez les individus isolés. La présence de mâles mûrs pendant les 21 premiers jours de vie imaginale n'a pas eu d'effet sur la production totale d'oeufs. L'hypothèse avancée est que ces effets de groupe (négatifs et positifs) sur le développement des ovaires d'Acheta domesticus ont reflété respectivement des accélérations et ralentissements de la vitellogenèse. La dépendance de l'induction de la vitellogenèse chez Acheta domesticus par les hormones juvéniles est connue (Benford, 1983) ainsi que les changements dans la quantité de produits neurosécréteurs, susceptibles d'être colorés dans la pars intercerebralis au cours du cycle reproductif (Bradley et Simpson, 1981). Nous ne savons pas si ces effets de groupement sur le développement des ovaires de grillon sont médiatisés par le système endocrine.

     

Tritium uptake and elimination by tissue-bound and body-water components in crickets (Acheta domesticus)

Tritium concentration ratios of less than unity (0·19) were determined for adult crickets which were at equilibrium for that particular instar with a tritium tagged food source. This phenomenon is interpreted as meaning that simple diffusion-equilibrium assumptions are not adequate for describing tritium movement in food chains when true equilibrium conditions are not met. Additional factors, such as rates of tritium assimilation and turnover for tissue-bound and body-water fractions, food habits, and duration of developmental stages must be considered along with environmental tritium concentrations in determining food chain transfers of this radionuclide.     

Threat-sensitive Predator Avoidance by Larval Pacific Treefrogs (Amphibia, Hylidae)

According to the threat-sensitive predator avoidance hypothesis, the intensity of a prey animal's antipredator response should reflect its vulnerability to a specific predator. In laboratory experiments, we observed the intensity of antipredator responses of Pacific treefrog ( Hyla regilla ) tadpoles to stimuli from caged larval northwestern salamander ( Ambystoma gracile ) predators. We varied the sizes of the tadpoles relative to the salamanders in an attempt to create differences in vulnerability of tadpoles to the salamander predators. After documenting the response of the tadpoles to the caged predator, we tested the tadpole's vulnerability to the predator by releasing the tadpole with the predator. We observed that as the relative size of the tadpoles to the caged salamanders increased, the antipredator response of the tadpoles decreased. These changes in behaviour closely mirrored changes in actual vulnerability to the predator. Our results provide experimental support for the threat-sensitive predator avoidance hypothesis.     

A Glimpse into the Microbiota of Marketed Ready-to-Eat Crickets ( Acheta domesticus )

The present study was aimed to get an insight into the bacterial biota of ready-to-eat small crickets (Acheta domesticus) already marketed in the European Union. 16S rRNA gene of the DNAs extracted from thirty-two samples of ready-to-eat crickets commercialized by 4 European Union producers located in Austria, Belgium, France and the Netherlands (2 batches per producer) was analyzed by Polymerase Chain Reaction–Denaturing Gradient Gel Electrophoresis (PCR–DGGE). The species belonging to the genera Hespellia, Ruminococcus and Clostridium were detected in samples from Austria, while those from genera Lysobacter, Staphylococcus and Clostridium were detected in samples from Belgium. Moreover, samples from France were characterized by Staphylococcus, Pseudomonas, and Hydrogenophilus genera. Finally, the genera Staphylococcus, Hydrogenophilus, Clostridium and Ruminococcus were identified in the samples produced in the Netherlands. When insects are intended for commercialization, rearing, processing and handling could affect the presence of the occurring microbial species. Hence, to assure a safe product, the need for a full standardization of production technologies, including feed supply as well as rearing and processing practices, is recommended.     

Cajal bodies (coiled bodies) in the nuclei of the house cricket (Acheta domesticus) oocytes

The morphology and fine structure of Cajal bodies (coiled bodies, CB) in the germinal vesicles (oocyte nuclei) of the house cricket, Acheta domesticus have been analyzed. It is shown that in the studied species CBs arise as early as in the youngest previtellogenic oocytes, and are located next to or within aggregations of multiple nucleoli. Surprisingly, two morphological types of CBs have been found in the analyzed specimens. On the basis of EM studies we suggest that they represent subsequent developmental stages of CB morphogenesis.     

Nanomechanical properties of wing membrane layers in the house cricket (Acheta domesticus Linnaeus)

Many insect wings change shape dynamically during the wingbeat cycle, and these deformations have the potential to confer energetic and aerodynamic benefits during flight. Due to the lack of musculature within the wing itself, the changing form of the wing is determined primarily by its passive response to inertial and aerodynamic forces. This response is in part controlled by the wing’s mechanical properties, which vary across the membrane to produce regions of differing stiffness. Previous studies of wing mechanical properties have largely focused on surface or bulk measurements, but this ignores the layered nature of the wing. In our work, we investigated the mechanical properties of the wings of the house cricket (Acheta domesticus) with the aim of determining differences between layers within the wing. Nanoindentation was performed on both the surface and the interior layers of cross-sectioned samples of the wing to measure the Young’s modulus and hardness of the outer- and innermost layers. The results demonstrate that the interior of the wing is stiffer than the surface, and both properties vary across the wing.     

Excretion in the house cricket (Acheta domesticus): fine structure of the Malpighian tubules

An ultrastructural analysis of the Malpighian tubules of the cricket, Acheta domesticus, is presented. The excretory system of the cricket is unusual in that the 112 Malpighian tubules do not attach directly to the gut, but fuse to form a bladder-like ampulla which is joined to the colon by a muscular ureter. The tubules have three structurally distinct segments and consist of four cell types. Attached by basal lamina to the outer surface of the distal tip are nodules, consisting of small cells on membranous stalks. These are presumed to serve as attachments to the body wall. The distal 20% of the tubule is hyaline, consisting of a monolayer of squamous cells that appear to be secretory. The mid-tubule comprises 75% of the total length and is the primary region for fluid secretion. It is also characterized by having large numbers of laminate spheres in the cytoplasm of the cells. The proximal 5% of each tubule consists of more columnar cells and may function in fluid resorption. The relationship between structural features and known physiological functions are discussed.     

Proteine in der Frühentwicklung der Grille (Acheta domesticus,Orthoptera)

Zusammenfassung Aus Grilleneiern wurden verschiedene Proteingemische gewonnen durch: Homogenisierung, Ultrabeschallung, fraktionierte Zentrifugation, Essigsäureextraktion und Säulenchromatographie an Hydroxyapatit. Die nach Acetonfällung in 8 M Harnstoff gelösten Proteine wurden durch SDS-Polyacrylamidelektrophorese aufgetrennt und densitometrisch analysiert. In Grilleneiern ließen sich durch Inkubation in¹⁴CO₂ Proteine radioaktiv markieren. Die Markierungsrate einzelner Proteinfraktionen wurde als Radioaktivität eluierter Gelfraktionen oder im Autoradiogramm von Gelscheiben gemessen. Die Verteilung der radioaktiv markierten Proteine im Elektropherogramm entsprach nicht dem Muster der gefärbten Proteinbanden und unterschied sich in charakteristischer Weise in den geprüften Stadien: Furchung (Omnipotenz), Keimanlage (Determination) und Keimstreif (Primäre Differenzierung).

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Proteins in early development of the cricket (Acheta domesticus, Orthoptera)

Summary Proteins in homogenates of yolk-rich cricket eggs were fractionated by sonication, differential centrifugation, acetic acid-extraction and column chromatography on hydroxyapatite and separated by SDS-polyacrylamide electrophoresis in 8 M urea. Radioactivity was introduced by incubating the eggs, which are impermeable to labeled amino acids, in a¹⁴CO₂-atmosphere.¹⁴C-label in protein extracts was resistant to hot TCA-extraction and was proved to be mainly in glutamic acid and aspartic acid. The profiles of radioactivity across the electropherogram as analysed by gel-fractionation and scintillation counting or by radioautography were found to be distinct from the pattern of stained protein-bands. During early development characteristic changes in the patterns of radioactive proteins occurred at the three stages tested: cleavage (omnipotency), germ-disc (determination) and germ-band (primary differentiation).

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Wir danken der Deutschen Forschungsgemeinschaft für die Unterstützung dieser Arbeit durch ein Ausbildungsstipendium (G. W.) und Sachbeihilfen.