One hundred years of phase polymorphism research in locusts.

One hundred years ago in 1921, Sir Boris Uvarov recognized that two locust species are one species but appearing in two different phases, a solitarious and a gregarious phase. As locust swarms are still a big problem affecting millions of people, basic research has tried to understand the causes for the transition between phases. This phenomenon of phase polymorphism, now called polyphenism, is a very complex multifactorial process and this short review will draw attention to this important aspect of insect research.

Role of the Insect Neuroendocrine System in the Response to Cold Stress.

Insects are the largest group of animals. They are capable of surviving in virtually all environments from arid deserts to the freezing permafrost of polar regions. This success is due to their great capacity to tolerate a range of environmental stresses, such as low temperature.

Descending octopaminergic neurons modulate sensory-evoked activity of thoracic motor neurons in stick insects.

Neuromodulatory neurons located in the brain can influence activity in locomotor networks residing in the spinal cord or ventral nerve cords of invertebrates. How inputs to and outputs of neuromodulatory descending neurons affect walking activity is largely unknown. With the use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and immunohistochemistry, we show that a population of dorsal unpaired median (DUM) neurons descending from the gnathal ganglion to thoracic ganglia of the stick insect contains the neuromodulatory amine octopamine.

Neural pathways in the pallial nerve and arm nerve cord revealed by neurobiotin backfilling in the cephalopod mollusk Octopus vulgaris.

Here, we report the findings after application of neurobiotin tracing to pallial and stellar nerves in the mantle of the cephalopod mollusk Octopus vulgaris and to the axial nerve cord in its arm. Neurobiotin backfilling is a known technique in other molluscs, but it is applied to octopus for the first time to be best of our knowledge. Different neural tracing techniques have been carried out in cephalopods to study the intricate neural connectivity of their nervous system, but mapping the nervous connections in this taxon is still incomplete, mainly due to the absence of a reliable tracing method allowing whole-mount imaging.

Ex vivo recordings reveal desert locust forelimb control is asymmetric.

Lateralized behaviours are widespread among the animals, including insects with their miniature brains, perhaps being a way of maximising neural capacity (reviewed in [1,2]). However, evidence for functional asymmetries in the neural circuitry itself is scarce. Here, using bilateral simultaneous recordings from the ex vivo nervous system of desert locusts, we show that the neural control of their forelimbs is asymmetric.

A population of descending tyraminergic/octopaminergic projection neurons of the insect deutocerebrum.

In this study, we describe a cluster of tyraminergic/octopaminergic neurons in the lateral dorsal deutocerebrum of desert locusts (Schistocerca gregaria) with descending axons to the abdominal ganglia. In the locust, these neurons synthesize octopamine from tyramine stress-dependently. Electrophysiological recordings in locusts reveal that they respond to mechanosensory touch stimuli delivered to various parts of the body including the antennae.

The functional connectivity between the locust leg pattern generators and the subesophageal ganglion higher motor center.

Higher motor centers and central pattern generators (CPGs) interact in the control of coordinated leg movements during locomotion throughout the animal kingdom. The subesophageal ganglion (SEG) is one of the insect head ganglia reported to have a role in the control of walking behavior. Here we explored the functional relations between the SEG and the thoracic leg CPGs in the desert locust.

Structural and Molecular Properties of Insect Type II Motor Axon Terminals.

A comparison between the axon terminals of octopaminergic efferent dorsal or ventral unpaired median neurons in either desert locusts () or fruit flies () across skeletal muscles reveals many similarities. In both species the octopaminergic axon forms beaded fibers where the boutons or varicosities form type II terminals in contrast to the neuromuscular junction (NMJ) or type I terminals. These type II terminals are immunopositive for both tyramine and octopamine and, in contrast to the type I terminals, which possess clear synaptic vesicles, only contain dense core vesicles.

Octopaminergic innervation and a neurohaemal release site in the antennal heart of the locust Schistocerca gregaria.

A detailed account is given by the octopaminergic innervation of the antennal heart in Schistocerca gregaria using various immunohistochemical methods. Anterograde axonal filling illustrates the unilateral innervation on the medial ventral surface of the pumping muscle of the antennal heart via the paired corpora cardiaca nerve III. In addition, antibody staining revealed that ascending axons of this nerve terminate at the ampullae of the antennal heart forming synaptoid structures and extensive neurohaemal release sites.

Professor Ernst Bresslau, founder of the Zoology Departments at the Universities of Cologne and Sao Paulo: lessons to learn from his life history.

In this article, the life history of the founding father of the departments of Zoology at the Universities of Cologne and Sao Paulo, Prof. Ernst Bresslau, is described on occasion of the establishing of the "Ernst Bresslau Guest Professorship" at the University of Cologne. His main scientific achievements are discussed, in particular his research on the evolutionary origin of the mammary apparatus, in addition to his broad interest in biological topics.

Rigidity and Flexibility: The Central Basis of Inter-Leg Coordination in the Locust.

Many motor behaviors, and specifically locomotion, are the product of an intricate interplay between neuronal oscillators known as central pattern generators (CPGs), descending central commands, and sensory feedback loops. The relative contribution of each of these components to the final behavior determines the trade-off between fixed movements and those that are carefully adapted to the environment. Here we sought to decipher the endogenous, default, motor output of the CPG network controlling the locust legs, in the absence of any sensory or descending influences.

Assessing segmental versus non-segmental features in the ventral nervous system of onychophorans (velvet worms).

Background: Due to their phylogenetic position as one of the closest arthropod relatives, studies of the organisation of the nervous system in onychophorans play a key role for understanding the evolution of body segmentation in arthropods. Previous studies revealed that, in contrast to the arthropods, segmentally repeated ganglia are not present within the onychophoran ventral nerve cords, suggesting that segmentation is either reduced or might be incomplete in the onychophoran ventral nervous system.

Results: To assess segmental versus non-segmental features in the ventral nervous system of onychophorans, we screened the nerve cords for various markers, including synapsin, serotonin, gamma-aminobutyric acid, RFamide, dopamine, tyramine and octopamine.

Drosophila FoxP mutants are deficient in operant self-learning.

Intact function of the Forkhead Box P2 (FOXP2) gene is necessary for normal development of speech and language. This important role has recently been extended, first to other forms of vocal learning in animals and then also to other forms of motor learning. The homology in structure and in function among the FoxP gene members raises the possibility that the ancestral FoxP gene may have evolved as a crucial component of the neural circuitry mediating motor learning.

Selective neuronal staining in tardigrades and onychophorans provides insights into the evolution of segmental ganglia in panarthropods.

Background: Although molecular analyses have contributed to a better resolution of the animal tree of life, the phylogenetic position of tardigrades (water bears) is still controversial, as they have been united alternatively with nematodes, arthropods, onychophorans (velvet worms), or onychophorans plus arthropods. Depending on the hypothesis favoured, segmental ganglia in tardigrades and arthropods might either have evolved independently, or they might well be homologous, suggesting that they were either lost in onychophorans or are a synapomorphy of tardigrades and arthropods. To evaluate these alternatives, we analysed the organisation of the nervous system in three tardigrade species using antisera directed against tyrosinated and acetylated tubulin, the amine transmitter serotonin, and the invertebrate neuropeptides FMRFamide, allatostatin and perisulfakinin.

Developmental and activity-dependent plasticity of filiform hair receptors in the locust.

A group of wind sensitive filiform hair receptors on the locust thorax and head makes contact onto a pair of identified interneuron, A4I1. The hair receptors' central nervous projections exhibit pronounced structural dynamics during nymphal development, for example, by gradually eliminating their ipsilateral dendritic field while maintaining the contralateral one. These changes are dependent not only on hormones controlling development but on neuronal activity as well.

Dynamic neural control of insect muscle metabolism related to motor behavior.

Skeletal muscle innervation differs between vertebrates and insects. Insect muscle fibers exhibit graded electrical potentials and are innervated by excitatory, inhibitory, and also neuromodulatory motoneurons. The latter form a unique class of unpaired neurons with bilaterally symmetrical axons that release octopamine to alter the efficacy of synaptic transmission and regulate muscle energy metabolism by activating glycolysis.

Neuromodulatory unpaired median neurons in the New Zealand tree weta, Hemideina femorata.

Wetas are ancient Gondwanan orthopterans (Anostostomatidae) with many species endemic to New Zealand. Like all Orthoptera they possess efferent neuromodulatory dorsal unpaired median (DUM) neurons, with bilaterally symmetrical axons, that are important components of motor networks. These neurons produce overshooting action potentials and are easily stimulated by a variety of external mechanosensory stimuli delivered to the body and appendages.

The auditory system of non-calling grasshoppers (Melanoplinae: Podismini) and the evolutionary regression of their tympanal ears.

Reduction of tympanal hearing organs is repeatedly found amongst insects and is associated with weakened selection for hearing. There is also an associated wing reduction, since flight is no longer required to evade bats. Wing reduction may also affect sound production.

A revision of brain composition in Onychophora (velvet worms) suggests that the tritocerebrum evolved in arthropods.

Background: The composition of the arthropod head is one of the most contentious issues in animal evolution. In particular, controversy surrounds the homology and innervation of segmental cephalic appendages by the brain. Onychophora (velvet worms) play a crucial role in understanding the evolution of the arthropod brain, because they are close relatives of arthropods and have apparently changed little since the Early Cambrian.

The role of octopamine in locusts and other arthropods.

The biogenic amine octopamine and its biological precursor tyramine are thought to be the invertebrate functional homologues of the vertebrate adrenergic transmitters. Octopamine functions as a neuromodulator, neurotransmitter and neurohormone in insect nervous systems and prompts the whole organism to "dynamic action". A growing number of studies suggest a prominent role for octopamine in modulating multiple physiological and behavioural processes in invertebrates, as for example the phase transition in Schistocerca gregaria.

Three-dimensional distribution of NO sources in a primary mechanosensory integration center in the locust and its implications for volume signaling.

Nitric oxide (NO) is an evolutionarily conserved mediator of neural plasticity. Because NO is highly diffusible, signals from multiple sources might combine in space and time to affect the same target. Whether such cooperative effects occur will depend on the effective signaling range and on the distances of NO sources to one another and to their targets.

The cloning, phylogenetic relationship and distribution pattern of two new putative GPCR-type octopamine receptors in the desert locust (Schistocerca gregaria).

The biogenic amine octopamine functions as a neuromodulator, neurotransmitter and neurohormone in insect nervous systems. It plays a prominent role in modulating multiple physiological and behavioural processes in invertebrates. Octopamine exerts its effects by binding to specific receptor proteins that belong to the superfamily of G protein-coupled receptors.

Postembryonic development of centrally generated flight motor patterns in the hawkmoth, Manduca sexta.

This study analyses the maturation of centrally generated flight motor patterns during metamorphosis of Manduca sexta. Bath application of the octopamine agonist chlordimeform to the isolated central nervous system of adult moths reliably induces fictive flight patterns in wing depressor and elevator motoneurons. Pattern maturation is investigated by chlordimeform application at different developmental stages.