The colony environment modulates sleep in honey bee workers

Effect of aminergic signaling on the humoral innate immunity response of Drosophila

Biogenic amines are crucial signaling molecules that modulate various physiological life functions both in vertebrates and invertebrates. In humans, these neurotransmitters influence the innate and adaptive immunity systems. In this work, we analyzed whether the aminergic neurotransmission of dopamine, serotonin, and octopamine could have an impact on the humoral innate immune response of Drosophila melanogaster. This is a powerful model system widely used to uncover the insect innate immunity mechanisms which are also conserved in mammals. We found that the neurotransmission of all these amines positively modulates the Toll-responsive antimicrobial peptide (AMP) drosomycin (drs) gene in adult flies infected with the Micrococcus luteus bacterium. Indeed, we showed that either blocking the neurotransmission in their specific aminergic neurons by expressing shibirets (Shits) or silencing the vesicular monoamine transporter gene (dVMAT) by RNAi caused a significantly reduced expression of the Toll-responsive drs gene. However, upon M. luteus infection, the block of aminergic transmission did not alter the expression of AMP attacin genes responding to the immune deficiency (Imd) and Toll pathways. Overall, our results not only reveal a neuroimmune function for biogenic amines in humoral immunity but also further highlight the complexity of the network controlling AMP gene regulation.

Using radio frequency identification and locomotor activity monitoring to assess sleep, locomotor, and foraging rhythmicity in bumblebees

Bumblebees are a key pollinator. Understanding the factors that influence the timing of sleep and foraging trips is important for efficient foraging and pollination. Here, we illustrate how individual locomotor activity monitoring and colony-wide radio frequency identification tracking can be combined to analyze the effects of agrochemicals like neonicotinoids on locomotor and foraging rhythmicity and sleep quantity/quality in bumblebees. We also highlight aspects of the design that can be adapted for other invertebrates or agrochemicals, allowing broader application of these techniques.

For complete details on the use and execution of this protocol, please refer to Tasman et al. (2020).

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Easy and reliable way of testing circadian rhythmicity and sleep in invertebrates

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Covers colony care, equipment adaptation, and setup and experimental protocol

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This protocol can be used to study the effects of any water soluble/liquid insecticide

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The multiple ways to adapt the protocol for other organisms are highlighted

Neonicotinoids disrupt circadian rhythms and sleep in honey bees

Honey bees are critical pollinators in ecosystems and agriculture, but their numbers have significantly declined. Declines in pollinator populations are thought to be due to multiple factors including habitat loss, climate change, increased vulnerability to disease and parasites, and pesticide use. Neonicotinoid pesticides are agonists of insect nicotinic cholinergic receptors, and sub-lethal exposures are linked to reduced honey bee hive survival. Honey bees are highly dependent on circadian clocks to regulate critical behaviors, such as foraging orientation and navigation, time-memory for food sources, sleep, and learning/memory processes. Because circadian clock neurons in insects receive light input through cholinergic signaling we tested for effects of neonicotinoids on honey bee circadian rhythms and sleep. Neonicotinoid ingestion by feeding over several days results in neonicotinoid accumulation in the bee brain, disrupts circadian rhythmicity in many individual bees, shifts the timing of behavioral circadian rhythms in bees that remain rhythmic, and impairs sleep. Neonicotinoids and light input act synergistically to disrupt bee circadian behavior, and neonicotinoids directly stimulate wake-promoting clock neurons in the fruit fly brain. Neonicotinoids disrupt honey bee circadian rhythms and sleep, likely by aberrant stimulation of clock neurons, to potentially impair honey bee navigation, time-memory, and social communication.

Sleep in Drosophila and Its Context

A prominent idea emerging from the study of sleep is that this key behavioural state is regulated in a complex fashion by ecologically and physiologically relevant environmental factors. This concept implies that sleep, as a behaviour, is plastic and can be regulated by external agents and changes in internal state. Drosophila melanogaster constitutes a resourceful model system to study behaviour. In the year 2000, the utility of the fly to study sleep was realised, and has since extensively contributed to this exciting field. At the centre of this review, we will discuss studies showing that temperature, food availability/quality, and interactions with conspecifics can regulate sleep. Indeed the relationship can be reciprocal and sleep perturbation can also affect feeding and social interaction. In particular, different environmental temperatures as well as gradual changes in temperature regulate when, and how much flies sleep. Moreover, the satiation/starvation status of an individual dictates the balance between sleep and foraging. Nutritional composition of diet also has a direct impact on sleep amount and its fragmentation. Likewise, aggression between males, courtship, sexual arousal, mating, and interactions within large groups of animals has an acute and long-lasting effect on sleep amount and quality. Importantly, the genes and neuronal circuits that relay information about the external environment and internal state to sleep centres are starting to be elucidated in the fly and are the focus of this review. In conclusion, sleep, as with most behaviours, needs the full commitment of the individual, preventing participation in other vital activities. A vast array of behaviours that are modulated by external and internal factors compete with the need to sleep and thus have a significant role in regulating it.

Sleep changes following intensive cognitive activity

Studies over the last 40 years have mainly investigated sleep structure changes as a result of wake duration, in the frame of the classical sleep regulation theories. However, wake intervals of the same duration can profoundly differ in their intensity, which actually reflects the degree of cognitive and physical activity. Data on how sleep can be modified by wake intensity changes (initially sparse and of little consistence) have become much more substantial, especially in the frame of the intense research debate on sleep-memory relationships. Our aim is to examine the vast repertoire of sleep modifications that depend on waking cognitive manipulations, highlighting the sleep features that appear most affected. By systematically addressing this issue, we want to set the basis for future research exploring both the specific nature of the mechanisms involved and the applicative psychosocial and clinical fall-outs, in terms of possible behavioural interventions for sleep quality improvement.

Behavioral flexibility promotes collective consistency in a social insect

Deciphering the mechanisms that integrate individuals and their behavior into a functional unit is crucial for our understanding of collective behaviors. We here present empirical evidence for the impressive strength of social processes in this integration. We investigated collective temperature homeostasis in bumblebee (Bombus terrestris) colonies and found that bees are less likely to engage in thermoregulatory fanning and do so with less time investment when confronted with heat stress in a group setting than when facing the same challenge alone and that this down-regulation of individual stimulus-response behavior resulted in a consistent proportion of workers in a group engaged in the task of fanning. Furthermore, the bees that comprised the subset of fanning individuals changed from trial to trial and participation in the task was predominately unpredictable based on previous response behavior. Our results challenge basic assumptions in the most commonly used class of models for task allocation and contrast numerous collective behavior studies that emphasize the importance of fixed inter-individual variation for the functioning of animal groups. We demonstrate that bumblebee colonies maintain within-group behavioral heterogeneity and a consistent collective response pattern based on social responsiveness and behavioral flexibility at the individual level.

Neuronal Mechanisms for Sleep/Wake Regulation and Modulatory Drive

Humans have been fascinated by sleep for millennia. After almost a century of scientific interrogation, significant progress has been made in understanding the neuronal regulation and functions of sleep. The application of new methods in neuroscience that enable the analysis of genetically defined neuronal circuits with unprecedented specificity and precision has been paramount in this endeavor. In this review, we first discuss electrophysiological and behavioral features of sleep/wake states and the principal neuronal populations involved in their regulation. Next, we describe the main modulatory drives of sleep and wakefulness, including homeostatic, circadian, and motivational processes. Finally, we describe a revised integrative model for sleep/wake regulation.

Nurse honeybee workers tend capped-brood, which does not require feeding, around-the-clock

“Nurse” honeybees tend brood around-the-clock with attenuated or no circadian rhythms, but the brood signals inducing this behavior remain elusive. We first tested the hypothesis that worker circadian rhythms are regulated by brood pheromones. We monitored locomotor activity of individually isolated nurse bees that were either exposed to various doses of larval extracts or synthetic brood ester pheromone (BEP). Bees orally treated with larvae extracts showed attenuated circadian rhythms in one of four tested colonies; a similar but statistically non-significant trend was seen in two additional colonies. Nurse bees treated with synthetic BEP showed rhythm attenuation in one of three tested colonies. Next, we tested the hypothesis that capped brood, which does not require feeding, nevertheless induces around-the-clock activity in nurses. By combining a new protocol that enables brood care by individually isolated nurse bees, detailed behavioral observations, and automatic high resolution monitoring of locomotor activity, we found that isolated nurses tended capped brood around-the-clock with attenuated circadian rhythms. Bees individually isolated in similar cages but without brood, showed strong circadian rhythms in locomotor activity and rest. This study shows for the first time that the need to feed hungry larvae is not the only factor accounting for around-the-clock activity in nurse bees. Our results further suggest that the transition between activity with and without circadian rhythms is not a simple switch triggered by brood pheromones. Around-the-clock tending may enhance brood development and health in multiple ways that may include improved larval feeding, thermoregulation and hygienic behavior.

A new device for monitoring individual activity rhythms of honey bees reveals critical effects of the social environment on behavior

Chronobiological studies of individual activity rhythms in social insects can be constrained by the artificial isolation of individuals from their social context. We present a new experimental set-up that simultaneously measures the temperature rhythm in a queen-less but brood raising mini colony and the walking activity rhythms of singly kept honey bees that have indirect social contact with it. Our approach enables monitoring of individual bees in the social context of a mini colony under controlled laboratory conditions. In a pilot experiment, we show that social contact with the mini colony improves the survival of monitored young individuals and affects locomotor activity patterns of young and old bees. When exposed to conflicting Zeitgebers consisting of a light–dark (LD) cycle that is phase-delayed with respect to the mini colony rhythm, rhythms of young and old bees are socially synchronized with the mini colony rhythm, whereas isolated bees synchronize to the LD cycle. We conclude that the social environment is a stronger Zeitgeber than the LD cycle and that our new experimental set-up is well suited for studying the mechanisms of social entrainment in honey bees.