Judith Reinhard

Biosystematics of Reticulitermes termites in Europe: morphological, chemical and molecular data

Summary: In Europe the most abundant naturally residing termite is the subterranean genus Reticulitermes (Rhinotermitidae). Six phenotypes of Reticulitermes have been identified on the basis of morphological, chemical (cuticular hydrocarbons and soldier defensive secretions), and molecular (enzymatic alleles and mitochondrial ND1 sequence) features. They are R. santonensis in western France, R. grassei in southwestern France, northwestern and southern Spain and Portugal, R. banyulensis in northeastern Spain, central area of the Iberian Peninsula and southwestern France, R. lucifugus in Italy and southeastern France, R. balkanensis in the Balkans and R. sp. nov., a recently identified urban phenotype resembling R. balkanensis, in northern Italy and southeastern France. R. santonensis is close kin to the American species R. flavipes. R. grassei, R. banyulensis and R. lucifugus belong to the same species complex. R. balkanensis and the new phenotype R. sp. nov. are close to R. santonensis regarding cuticular hydrocarbons, to the lucifugus complex regarding DNA and to R. clypeatus from Israel regarding morphology. The species status of these genotypes has been confirmed by the mechanisms of species isolation. Prevention of hybridization depends on the method of colony formation in each species. Swarming dates, differences in pheromones, and infertility prevent hybridization by sexual alates. Interspecific aggression between workers prevents hybridization by neotenics. Behavioral and molecular studies have provided many data on the genetic structure of nests, which varies according to species and location. All colonies of R. santonensis are open all year. The colonies of R. grassei in southern areas and all colonies of R. banyulensis are closed families with generally a single reproductive couple. The colonies of R. grassei in northern areas and the colonies of R. lucifugus are open in the summer and closed in the winter. Based on the here presented data, the taxonomy and the speciation of the Reticulitermes genus in Europe are discussed.

Floral scents induce recall of navigational and visual memories in honeybees

SUMMARY During foraging flights, honeybees learn visual and chemical cues associated with a food source. We investigated whether learned olfactory cues can trigger visual and navigational memories in honeybees that assist them in navigating back to a known food source. In a series of experiments, marked bees were trained to forage at one or more sugar water feeders, placed at different outdoor locations and carrying different scents or colours. We then tested the ability of these bees to recall the locations (or colours) of these food sites and to fly to them, when the training scents were blown into the hive, and the scents and food at the feeders were removed. The results show that (1) bees, trained to a single-scented feeder at a given location, can be induced to fly to the same location by blowing the scent into the hive; (2) bees, trained to two feeders, each placed at a different location and carrying a different scent, can be induced to fly to either location by blowing the appropriate scent into the hive; and (3) bees, trained to two feeders, each decorated with a different colour and carrying a different scent, can be induced to find a feeder of either colour by blowing the appropriate scent into the hive. Thus, familiar scents can trigger navigational and visual memories in experienced bees. Our findings suggest that the odour and taste of the nectar samples that are distributed by successful foragers on returning to the hive, may trigger recall of navigational memories associated with the food site in experienced recruits and, thus, facilitate their navigation back to the site.

Systematic search for food in the subterranean termite Reticulitermes santonensis De Feytaud (Isoptera, Rhinotermitidae)

Summary: The search for food in subterranean termites is investigated in the French species Reticulitermes santonensis De Feytaud (Isoptera, Rhinotermitidae). Not accompanied by soldiers, only few pioneer workers explore a new territory systematically in every direction by means of short exploratory trails (median: 1.3 cm). Following these trails, termites build subterranean tunnels and/or galleries in the open, hereby forming an extensive regularly branched net. Food is detected over distance by perceiving volatiles emanating from the wood. Then foragers appear more frequently and undertake longer exploratory runs (up to 15 cm), which are directed towards the odour source. Following contact with the wood, sucessful workers return to the nest precisely along their exploratory trail and hereby lay a recruitment trail. This recruitment trail is immediately followed by further workers as well as by single soldiers. Following the course of this trail, termites build a non‐branched subterranean tunnel or a gallery above ground leading straight to the wood. This direct access requires less investment and provides workers with a shelter ensuring a rapid and safe exploitation of the food source.

Interspecific variation in terpenoid composition of defensive secretions of European Reticulitermes termites

Sixteen terpene compounds were isolated from the soldier defensive secretions of seven European termite taxa of the genus Reticulitermes (Isoptera, Rhinotermitidae). We describe species-specific mixtures of monoterpenes (α-pinene, β-pinene, limonene), sesquiterpenes (germacrene C, germacrene A, germacrene B, β-selinene, δ-selinene, γ-selinene, (E)-β-farnesene, γ-cadinene, nerolidol), diterpenes (geranyl linalool, geranyl geraniol, geranyl geranial), and one sesterterpene (geranyl farnesol). Compounds were purified by HPLC and their structures determined by means of MS spectrometry, or 1D and 2D NMR spectroscopy. Comparison of two different analytical approaches, GC-MS and HPLC with subsequent NMR spectroscopy, revealed Cope rearrangement of germacrene A, germacrene B, and germacrene C to the respective β-elemene, γ-elemene, and δ-elemene under GC conditions, thus demonstrating the limits for this analytical approach. The species-specific compound composition provides insight into taxonomy and species origin of European Reticulitermes. The biological significance of the species-specific composition of Reticulitermes defensive secretions is briefly discussed.

Sensory regulation of neuroligins and neurexin I in the honeybee brain.

Background Neurexins and neuroligins, which have recently been associated with neurological disorders such as autism in humans, are highly conserved adhesive proteins found on synaptic membranes of neurons. These binding partners produce a trans-synaptic bridge that facilitates maturation and specification of synapses. It is believed that there exists an optimal spatio-temporal code of neurexin and neuroligin interactions that guide synapse formation in the postnatal developing brain. Therefore, we investigated whether neuroligins and neurexin are differentially regulated by sensory input using a behavioural model system with an advanced capacity for sensory processing, learning and memory, the honeybee. Methodology/Principal Findings Whole brain expression levels of neuroligin 1–5 (NLG1–5) and neurexin I (NrxI) were estimated by qRT-PCR analysis in three different behavioural paradigms: sensory deprivation, associative scent learning, and lateralised sensory input. Sensory deprived bees had a lower level of NLG1 expression, but a generally increased level of NLG2–5 and NrxI expression compared to hive bees. Bees that had undergone associative scent training had significantly increased levels of NrxI, NLG1 and NLG3 expression compared to untrained control bees. Bees that had lateralised sensory input after antennal amputation showed a specific increase in NLG1 expression compared to control bees, which only happened over time. Conclusions/Significance Our results suggest that (1) there is a lack of synaptic pruning during sensory deprivation; (2) NLG1 expression increases with sensory stimulation; (3) concomitant changes in gene expression suggests NrxI interacts with all neuroligins; (4) there is evidence for synaptic compensation after lateralised injury.

Big ideas for small brains: what can psychiatry learn from worms, flies, bees and fish?

While the research community has accepted the value of rodent models as informative research platforms, there is less awareness of the utility of other small vertebrate and invertebrate animal models. Neuroscience is increasingly turning to smaller, non-rodent models to understand mechanisms related to neuropsychiatric disorders. Although they can never replace clinical research, there is much to be learnt from ‘small brains’. In particular, these species can offer flexible genetic ‘tool kits’ that can be used to explore the expression and function of candidate genes in different brain regions. Very small animals also offer efficiencies with respect to high-throughput screening programs. This review provides a concise overview of the utility of models based on worm, fruit fly, honeybee and zebrafish. Although these species may have small brains, they offer the neuropsychiatric research community opportunities to explore some of the most important research questions in our field.

Hydroquinone: A general phagostimulating pheromone in termites

The organization of termite societies depends predominantly on intraspecific chemical signals (pheromones) produced by exocrine glands, which induce and modulate individual behavioral responses. Here, the saliva-producing labial glands of termites were investigated with respect to their pheromonal role in communal food exploitation of termite colonies. From these glands, we identified for the first time hydroquinone (1,4-dihydroxybenzene) as a phagostimulating pheromone in the Australian termite species Mastotermes darwiniensis. Hydroquinone is released from the labial glands of termite workers and applied onto the food. It stimulates nestmates to feed at the spot of application and is, thus, employed to mark feeding sites. No synergistic effect with other identified labial gland compounds, such as glucose, inositol, and arbutin, was evident. Significantly, we show that termite species from all over the world, irrespective of taxonomic position and biological traits, produce and employ hydroquinone as phagostimulating signal. The use of the same chemical signal throughout an order is a unique phenomenon, not reported before in animals. Its possible biosynthetic pathway, ecological significance, and evolution are discussed.

Trail communication during foraging and recruitment in the subterranean termite Reticulitermes santonensis De Feytaud (Isoptera, Rhinotermitidae)

The search for food in the French subterranean termite Reticulitermes santonensis De Feytaud is organized in part by chemical trails laid with the secretion of their abdominal sternal gland. Trail-laying and -following behavior of R. santonensis was investigated in bioassays. During foraging for food termites walk slowly (on average, 2.3 mm/s) and lay a dotted trail by dabbing the abdomen at intervals on the ground. When food is discovered they return at a quick pace (on average, 8.9 mm/s) to the nest, laying a trail for recruiting nestmates to the food source. While laying this recruitment trail the workers drag the abdomen continuously on the ground. The recruitment trail is highly attractive: it is followed within a few seconds, by more nestmates, and at a quicker pace (on average, 6.4 mm/s) than foraging trails (on average, 2.9 mm/s). The difference between foraging and recruitment trails in R. santonensis could be attributed to different quantities of trail pheromone. A caste-specific difference in trail pheromone thresholds, with workers of R. santonensis being more sensitive to trails than soldiers, was also documented: soldiers respond only to trails with a high concentration of trail pheromone.

The moment before touchdown: landing manoeuvres of the honeybee Apis mellifera

SUMMARY Although landing is a crucial part of insect flight, it has attracted relatively little study. Here, we investigate, for the first time, the final moments of a honeybees (Apis mellifera) landing manoeuvre. Using high-speed video recordings, we analyse the behaviour of bees as they approach and land on surfaces of various orientations. The bees enter a stable hover phase, immediately prior to touchdown. We have quantified behaviour during this hover phase and examined whether it changes as the tilt of the landing surface is varied from horizontal (floor), through sloped (uphill) and vertical (wall), to inverted (ceiling). The bees hover at a remarkably constant distance from the surface, irrespective of its tilt. Body inclination increases progressively as the tilt of the surface is increased, and is accompanied by an elevation of the antennae. The tight correlation between the tilt of the surface, and the orientation of the body and the antennae, indicates that the bees visual system is capable of inferring the tilt of the surface, and pointing the antennae toward it. Touchdown is initiated by extending the appendage closest to the surface, namely, the hind legs when landing on horizontal or sloping surfaces, and the front legs or antennae when landing on vertical surfaces. Touchdown on inverted surfaces is most likely triggered by a mechanosensory signal from the antennae. Evidently, bees use a landing strategy that is flexibly tailored to the varying topography of the terrain.

Odor memories regulate olfactory receptor expression in the sensory periphery.

Odor learning induces structural and functional modifications throughout the olfactory system, but it is currently unknown whether this plasticity extends to the olfactory receptors (Or) in the sensory periphery. Here, we demonstrate that odor learning induces plasticity in olfactory receptor expression in the honeybee, Apis mellifera. Using quantitative RT‐PCR analysis, we show that six putative floral scent receptors were differentially expressed in the bee antennae depending on the scent environment that the bees experienced. Or151, which we characterized using an in vitro cell expression system as a broadly tuned receptor binding floral odorants such as linalool, and Or11, the specific receptor for the queen pheromone 9‐oxo‐decenoic acid, were significantly down‐regulated after honeybees were conditioned with the respective odorants in an olfactory learning paradigm. Electroantennogram recordings showed that the neural response of the antenna was similarly reduced after odor learning. Long‐term odor memory was essential for inducing these changes, suggesting that the molecular mechanisms involved in olfactory memory also regulate olfactory receptor expression. Our study demonstrates for the first time that olfactory receptor expression is experience‐dependent and modulated by scent conditioning, providing novel insight into how molecular regulation at the periphery contributes to plasticity in the olfactory system.