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Mating success depends on many factors, but first of all, a male and a female need to meet at the same place and time. The circadian clock is an endogenous system regulating activity and sex-related behaviors in animals. We studied bumble bees (Bombus terrestris) in which the influence of circadian rhythms on sexual behavior has been little explored. We characterized circadian rhythms in adult emergence and locomotor activity under different illumination regimes for males and gynes (unmated queens). We developed a method to monitor adult emergence from the pupal cocoon and found no circadian rhythms in this behavior for either males or gynes. These results are not consistent with the hypothesis that the circadian clock regulates emergence from the pupa in this species. Consistent with this premise, we found that both gynes and males do not show circadian rhythms in locomotor activity during the first 3 days after pupal emergence, but shortly after developed robust circadian rhythms that are readily shifted by a phase delay in illumination regime. We conclude that the bumble bees do not need strong rhythms in adult emergence and during early adult life in their protected and regulated nest environment, but do need strong activity rhythms for timing flights and mating-related behaviors. Next, we tested the hypothesis that the locomotor activity of males and gynes have a similar phase, which may improve mating success. We found that both males and gynes have strong endogenous circadian rhythms that are entrained by the illumination regime, but males show rhythms at an earlier age, their rhythms are stronger, and their phase is slightly advanced relative to that of gynes. An earlier phase may be advantageous to males competing to mate a receptive gyne. Our results are consistent with the hypothesis that sex-related variations in circadian rhythms is shaped by sexual selection. [ABSTRACT FROM AUTHOR]

Social organization is commonly dynamic, with extreme examples in annual social insects, but little is known about the underlying signals and mechanisms. Bumble bee larvae with close contact to a queen do not differentiate into gynes, pupate at an earlier age, and are commonly smaller than siblings that do not contact a queen. We combined detailed observations, proteomics, microRNA transcriptomics, and gland removal surgery to study the regulation of brood development and division of labor in the annual social bumble bee Bombus terrestris. We found that regurgitates fed to larvae by queens and workers differ in their protein and microRNA composition. The proteome of the regurgitate overlaps significantly with that of the mandibular (MG) and hypopharyngeal glands (HPG), suggesting that these exocrine glands are sources of regurgitate proteins. The proteome of the MG and HPG, but not the salivary glands, differs between queens and workers, with caste-specificity preserved for the MG and regurgitate proteomes. Queens subjected to surgical removal of the MG showed normal behavior, brood care, and weight gain, but failed to shorten larval development. These findings suggest that substances in the queen MG are fed to larvae and influence their developmental program. We suggest that when workers emerge and contribute to larval feeding, they dilute the effects of the queen substances, until she can no longer manipulate the development of all larvae. Longer developmental duration may allow female larvae to differentiate into gynes rather than to workers, mediating the colony transition from the ergonomic to the reproductive phase. [ABSTRACT FROM AUTHOR]

Simple Summary: Honey bees are famous for their capacity to precisely time their visits to flowers to maximize food reward, but it is not known whether similar "time-memory" exists in other bees that forage over shorter distances from their nests. Here, we tested whether bumble bees that live in smaller colonies can associate reward with time of day and color. We trained bumble bee workers to feed on yellow or blue artificial flowers during either the morning or evening, respectively. During the test day, we presented non-rewarding flowers and recorded the behavior of the foraging bees. We found that trained bees preferred yellow flowers during the time corresponding to the morning training time and blue flowers during the time corresponding to the evening training time. These observations show that bumble bees can associate time of day with a specific color and reward, suggesting that time-memory is not limited to species such as honey bees that forage over long distances and time periods. Circadian clocks regulate ecologically important complex behaviors in honey bees, but it is not clear whether similar capacities exist in other species of bees. One key behavior influenced by circadian clocks is time-memory, which enables foraging bees to precisely time flower visitation to periods of maximal pollen or nectar availability and reduces the costs of visiting a non-rewarding flower patch. Bumble bees live in smaller societies and typically forage over shorter distances than honey bees, and it is therefore not clear whether they can similarly associate reward with time of day. We trained individually marked bumble bee (Bombus terrestris) workers to forage for sugar syrup in a flight cage with yellow or blue feeders rewarding either during the morning or evening. After training for over two weeks, we recorded all visitations to colored feeders filled with only water. We performed two experiments, each with a different colony. We found that bees tended to show higher foraging activity during the morning and evening training sessions compared to other times during the day. During the test day, the trained bees were more likely to visit the rewarding rather than the non-rewarding colored feeders at the same time of day during the test sessions, indicating that they associated time of day and color with the sugar syrup reward. These observations lend credence to the hypothesis that bumble bees have efficient time-memory, indicating that this complex behavior is not limited to honey bees that evolved sophisticated social foraging behaviors over large distances. [ABSTRACT FROM AUTHOR]

Honey bee queens show extreme fecundity, commonly laying more than a thousand eggs in a single day. It has proven challenging to study the temporal organization of egg-laying behavior because queens are typically active around the clock in the dark cavity of a densely populated nest. To contend with this challenge, we developed two novel methods allowing detailed monitoring of queen activity and egg laying. We first adapted a high-resolution, continuous, tracking system allowing to track the position of barcode-tagged queens in observation hives with colonies foraging outside. We found that the queen is active ~96% of the day with typically no diurnal rhythm. Next, we developed a new laboratory procedure to monitor egg laying at single egg resolution under different light regimes. We found that under constant darkness (DD) and temperature conditions, queens laid eggs with no circadian rhythms. Queen fecundity was severely reduced under constant light (LL). Under a 12:12 illumination regime, queen fecundity was comparable to under constant darkness, with a higher number of eggs during the light phase. These daily rhythms in egg laying continued when these queens were released to DD conditions, suggesting that egg-laying rhythms are influenced by endogenous circadian clocks. These results suggest that honey bee queens are active and lay eggs around the clock with no diurnal rhythms. Light has complex influences on these behaviors, but more studies are needed to determine whether these effects reflect the influence of light directly on the queen or indirectly by affecting workers that interact with the queen. [ABSTRACT FROM AUTHOR]

The systemic neonicotinoid insecticides are considered as one of the key culprits contributing to ongoing declines in pollinator health and abundance. Bumblebees are among the most important pollinators of temperate zone plants, making their susceptibility to neonicotinoid exposure of great concern. We report that bumblebee (Bombus terrestris) colonies exposed to field-realistic concentrations of the commonly used neonicotinoid Imidacloprid grew slower, consumed less food, and produced fewer workers, males and gynes, but unexpectedly produced larger workers compared to control colonies. Behavioural observations show that queens in pesticide-treated colonies spend more time inactive and less time caring for the brood. We suggest that the observed effects on brood body size are driven by a decreased queen ability to manipulate the larva developmental programme. These findings reveal an intricate and previously unknown effect of insecticides on the social interactions controlling brood development in social insect colonies. Insecticide influences on the social mechanisms regulating larval development are potentially detrimental for bumblebees, in which body size strongly influences both caste differentiation and the division of labour among workers, two organization principles of insect societies. [ABSTRACT FROM AUTHOR]

Assuming that some wild bee populations are resource limited [[56]], the possible competition with early arriving bumble bees (as well as honey bees) may imply that some native bees need to work harder and invest more time and energy in order to collect the proteins (i.e., pollen) needed for provisioning their offspring. Bumble bees visited both pollen- and nectar-rewarding flowers earlier than the wild bees, and the pollen-rewarding flowers earlier than the carpenter bees, but with no significant difference compared to the honey bee for both type of flowers (Table 4). Bumble bees (and to lesser extent honey bees) arrive to pollen-rewarding flowers earlier in the morning and have the opportunity to deplete pollen rewards before the later arrival of the local wild bees ( I Xylocopa i and other wild bee taxa). [Extracted from the article]

The apiary discovered in Stratum V at Tel Reḥov in 2005–2007 remains unique in the archaeology of the ancient Near East. Here the authors briefly summarize the data previously published in this journal and add results of new studies, mainly concerning the identification of ancient charred bees trapped in burnt honeycombs found in the hives. Measurements of two wings and one leg, and statistical work based on existing database of modern subspecies, are inconsistent with the Syrian subspecies local to Israel (Apis meliferra syriaca), but were found to be similar to the Anatolian bee (Apis meliferra anatoliaca). We discuss the implications of this result, suggesting trade relations with southern Anatolia. The authors suggest that the beeswax was perhaps related to the copper-based metallurgical industry that entailed casting in the lost wax method, at a time when the copper trade based on the Arabah mines was at its peak. [ABSTRACT FROM AUTHOR]

Honey bees live in colonies containing tens of thousands of workers that coordinate their activities to produce efficient colony-level behavior. In free-foraging colonies, nest bees are entrained to the forager daily phase of activity even when experiencing conflicting light-dark illumination regime, but little is known on the cues mediating this potent social synchronization. We monitored locomotor activity in an array of individually caged bees in which we manipulated the contact with neighbour bees. We used circular statistics and coupling function analyses to estimate the degree of social synchronization. We found that young bees in cages connected to cages housing foragers showed stronger rhythms, better synchronization with each other, higher coupling strength, and a phase more similar to that of the foragers compared to similar bees in unconnected cages. These findings suggest that close distance contacts are sufficient for social synchronization or that cage connection facilitated the propagation of time-giving social cues. Coupling strength was higher for bees placed on the same tray compared with bees at a similar distance but on a different tray, consistent with the hypothesis that substrate borne vibrations mediate phase synchronization. Additional manipulation of the contact between cages showed that social synchronization is better among bees in cages connected with tube with a single mesh partition compared to sealed tubes consistent with the notion that volatile cues act additively to substrate borne vibrations. These findings are consistent with self-organization models for social synchronization of activity rhythms and suggest that the circadian system of honey bees evolved remarkable sensitivity to non-photic, non-thermal, time giving entraining cues enabling them to tightly coordinate their behavior in the dark and constant physical environment of their nests. [ABSTRACT FROM AUTHOR]

Many animals benefit from synchronizing their daily activities with conspecifics. In this hybrid paper, we first review recent literature supporting and extending earlier evidence for a lack of clear relationship between the level of sociality and social entrainment of circadian rhythms. Social entrainment is specifically potent in social animals that live in constant environments in which some or all individuals do not experience the ambient day-night cycles. We next focus on highly social honeybees in which there is good evidence that social cues entrain the circadian clocks of nest bees and can override the influence of conflicting light-dark cycles. The current understanding of social synchronization in honeybees is consistent with self-organization models in which surrogates of forager activity, such as substrate-borne vibrations and colony volatiles, entrain the circadian clocks of bees dwelling in the dark cavity of the nest. Finally, we present original findings showing that social synchronization is effective even in an array of individually caged callow bees placed on the same substrate and is improved for bees in connected cages. These findings reveal remarkable sensitivity to social time-giving cues and show that bees with attenuated rhythms (weak oscillators) can nevertheless be socially synchronized to a common phase of activity. This article is part of the theme issue 'Synchrony and rhythm interaction: from the brain to behavioural ecology'. [ABSTRACT FROM AUTHOR]

Background: The developmental fates of offspring have the potential to be influenced by the identity of their caregivers and by the nature of the care that they receive. In animals that exhibit both parental and alloparental care, such as the annually eusocial insects, the influence of care-giver identity can be directly assessed to yield mechanistic and evolutionary insights into the origins and elaboration of brood care. Here, we performed a comparative investigation of maternal and worker brood care in bumble bees, a pollinator group where mothers (queens) rear the first offspring in the nest, and then daughters (workers) assume this role upon their emergence. Specifically, we compared the effects of queen and worker brood care on offspring development and also offspring performance, for a set of traits related to sensory biology, learning, and stress resistance. Results: We found that queen-reared workers were smaller-bodied than worker-reared offspring, suggesting that bumble bee queens influence body size determination in their offspring. We also found that queen-reared workers were more resistant to starvation, which might be beneficial for early nesting success. These maternal influences could not be explained by feeding rate, given that we detected a similar offspring feeding frequency in both queens and workers. Conclusion: Bumble bee queens have a unique influence on the development of the first offspring in the nest, which they rear, relative to worker-reared workers. We propose that bumble bee brood care has been shaped by a suite of evolutionary and ecological factors, which might include a maternal influence on traits that promote survival of incipient colonies. [ABSTRACT FROM AUTHOR]

The rapid increase in "big data" during the postgenomic era makes it crucial to appropriately measure the level of social complexity in comparative studies. We argue that commonly used qualitative classifications lump together species showing a broad range of social complexity and falsely imply that social evolution always progresses along a single linear stepwise trajectory that can be deduced from comparing extant species. To illustrate this point, we compared widely used social complexity measures in "primitively eusocial" bumble bees with "advanced eusocial" stingless bees, honey bees, and attine ants. We find that a single species can have both higher and lower levels of complexity compared with other taxa, depending on the social trait measured. We propose that measuring the complexity of individual social traits switches focus from semantic discussions and offers several directions for progress. First, quantitative social traits can be correlated with molecular, developmental, and physiological processes within and across lineages of social animals. This approach is particularly promising for identifying processes that influence or have been affected by social evolution. Second, key social complexity traits can be combined into multidimensional lineage-specific quantitative indices, enabling fine-scale comparison across species that are currently bundled within the same level of social complexity. [ABSTRACT FROM AUTHOR]

We studied phototaxis, the directional movement relative to light, in the bumble bee Bombus terrestris. We first developed and validated a MATLAB-based system enabling reliable high-resolution tracking of a bee and a measurement of her distance relative to a changing LED light source. Using this system, we found in all our experiments that workers show positive phototaxis. The strength of the phototactic response was influenced by body size but not age, and this effect was significant when the light source was weak. In a separate experiment, foragers showed stronger phototactic response compared with nurses only in one of two trials in which they were larger and tested with weak light intensity. The evidence that phototaxis is associated with size-based division of labor in the bumble bee and with age-related division of labor in the honey bee lends credence to response threshold models implicating the response to light in the organization of division of labor in cavity dwelling social insects. [ABSTRACT FROM AUTHOR]

Internal circadian clocks organize animal behavior and physiology and are entrained by ecologically relevant external time-givers such as light and temperature cycles. In the highly social honey bee, social time-givers are potent and can override photic entrainment, but the cues mediating social entrainment are unknown. Here, we tested whether substrate-borne vibrations and hive volatiles can mediate social synchronization in honey bees. We first placed newly emerged worker bees on the same or on a different substrate on which we placed cages with foragers entrained to ambient day-night cycles, while minimizing the spread of volatiles between cages. In the second experiment, we exposed young bees to constant airflow drawn from either a free-foraging colony or a similar-size control hive containing only heated empty honeycombs, while minimizing transfer of substrate-borne vibrations between cages. After 6 days, we isolated each focal bee in an individual cage in an environmental chamber and monitored her locomotor activity. We repeated each experiment 5 times, each trial with bees from a different source colony, monitoring a total of more than 1000 bees representing diverse genotypes. We found that bees placed on the same substrate as foragers showed a stronger phase coherence and a phase more similar to that of foragers compared with bees placed on a different substrate. In the second experiment, bees exposed to air drawn from a colony showed a stronger phase coherence and a phase more similar to that of foragers compared with bees exposed to air from an empty hive. These findings lend credence to the hypothesis that surrogates of activity entrain circadian rhythms and suggest that multiple social cues can act in concert to entrain social insect colonies to a common phase. [ABSTRACT FROM AUTHOR]

Extracting complex interactions (i.e., dynamic topologies) has been an essential, but difficult, step toward understanding large, complex, and diverse systems including biological, financial, and electrical networks. However, reliable and efficient methods for the recovery or estimation of network topology remain a challenge due to the tremendous scale of emerging systems (e.g., brain and social networks) and the inherent nonlinearity within and between individual units. We develop a unified, data-driven approach to efficiently infer connections of networks (ICON). We apply ICON to determine topology of networks of oscillators with different periodicities, degree nodes, coupling functions, and time scales, arising in silico, and in electrochemistry, neuronal networks, and groups of mice. This method enables the formulation of these large-scale, nonlinear estimation problems as a linear inverse problem that can be solved using parallel computing. Working with data from networks, ICON is robust and versatile enough to reliably reveal full and partial resonance among fast chemical oscillators, coherent circadian rhythms among hundreds of cells, and functional connectivity mediating social synchronization of circadian rhythmicity among mice over weeks. [ABSTRACT FROM AUTHOR]

The insect antennae receive olfactory information from the environment. In some insects, it has been shown that antennal responsiveness is dynamically regulated by circadian clocks. However, it is unknown how general this phenomenon is and what functions it serves. Circadian regulation in honeybee workers is particularly interesting in this regard because they show natural task-related chronobiological plasticity. Forager bees show strong circadian rhythms in behavior and brain gene expression, whereas nurse bees tend brood around-the-clock and have attenuated circadian rhythms in activity and whole-brain gene expression. Here, we tested the hypothesis that there is task-related plasticity in circadian rhythms of antennal responsiveness to odorants in worker honeybees. We used electroantennogram (EAG) to measure the antennal responsiveness of nurses and foragers to general odorants and pheromones around the day. The capacity to track 10-Hz odorant pulses varied with time of day for both task groups but with different phases. The antennal pulse-tracking capacity was higher during the subjective day for the day-active foragers, whereas it was better during the night for around-the-clock active nurses. The task-related phases of pulse-tracking rhythms were similar for all the tested stimuli. We also found evidence for circadian rhythms in the EAG response magnitude of foragers but not of nurses. To the best of our knowledge, these results provide the first evidence for circadian regulation of antennal olfactory responsiveness and odorant pulse-tracking capacity in bees or any other hymenopteran insect. Importantly, our study shows for the first time that the circadian phase of olfactory responsiveness may be socially regulated. [ABSTRACT FROM AUTHOR]

The interactions between flowering plants and insect pollinators shape ecological communities and provide one of the best examples of coevolution. Although these interactions have received much attention in both ecology and evolution, their temporal aspects are little explored. Here we review studies on the circadian organization of pollination-related traits in bees and flowers. Research, mostly with the honeybee, Apis mellifera, has implicated the circadian clock in key aspects of their foraging for flower rewards. These include anticipation, timing of visits to flowers at specified locations and time-compensated sun-compass orientation. Floral rhythms in traits such as petal opening, scent release and reward availability also show robust daily rhythms. However, in only few studies was it possible to adequately determine whether these oscillations are driven by external time givers such as light and temperature cycles, or endogenous circadian clocks. The interplay between the timing of flower and pollinator rhythms may be ecologically significant. Circadian regulation of pollination-related traits in only few species may influence the entire pollination network and thus affect community structure and local biodiversity. We speculate that these intricate chronobiological interactions may be vulnerable to anthropogenic effects such as the introduction of alien invasive species, pesticides or environmental pollutants. [ABSTRACT FROM AUTHOR]

Most processes within organisms, and most interactions between organisms and their environment, have distinct time profiles. The temporal coordination of such processes is crucial across levels of biological organization, but disciplines differ widely in their approaches to study timing. Such differences are accentuated between ecologists, who are centrally concerned with a holistic view of an organism in relation to its external environment, and chronobiologists, who emphasize internal timekeeping within an organism and the mechanisms of its adjustment to the environment. We argue that ecological and chronobiological perspectives are complementary, and that studies at the intersection will enable both fields to jointly overcome obstacles that currently hinder progress. However, to achieve this integration, we first have to cross some conceptual barriers, clarifying prohibitively inaccessible terminologies. We critically assess main assumptions and concepts in either field, as well as their common interests. Both approaches intersect in their need to understand the extent and regulation of temporal plasticity, and in the concept of 'chronotype', i.e. the characteristic temporal properties of individuals which are the targets of natural and sexual selection. We then highlight promising developments, point out open questions, acknowledge difficulties and propose directions for further integration of ecological and chronobiological perspectives through Wild Clock research. [ABSTRACT FROM AUTHOR]

'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 exposed to either various doses of larval extract or synthetic brood ester pheromone (BEP). Bees orally treated with larval extract showed attenuated circadian rhythms in one of four tested colonies; a similar but statistically non-significant trendwas 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-theclock tending may enhance brood development and health in multiple ways that include improved larval feeding, thermoregulation or hygienic behavior. [ABSTRACT FROM AUTHOR]

The emergence of eusociality ("true sociality") in several insect lineages represents one of the most successful evolutionary adaptations in the animal kingdom in terms of species richness and global biomass. In contrast to solitary insects, eusocial insects evolved a set of unique behavioral and physiological traits such as reproductive division of labor and cooperative brood care, which likely played a major role in their ecological success. The molecular mechanisms that support the social regulation of behavior in eusocial insects, and their evolution, are mostly unknown. The recent whole-genome sequencing of several eusocial insect species set the stage for deciphering the molecular and genetic bases of eusociality, and the possible evolutionary modifications that led to it. Studies of mRNA expression patterns in the brains of diverse eusocial insect species have indicated that specific social behavioral states of individual workers and queens are often associated with particular tissue-specific transcriptional profiles. Here, we discuss recent findings that highlight the role of non-coding microRNAs (miRNAs) in modulating traits associated with reproductive and behavioral divisions of labor in eusocial insects. We provide bioinformatic and phylogenetic data, which suggest that some Hymenoptera-specific miRNA may have contributed to the evolution of traits important for the evolution of eusociality in this group. [ABSTRACT FROM AUTHOR]

One of the most important and evolutionary conserved roles of sleep is the processing and consolidation of information acquired during wakefulness. In both insects and mammals, environmental and social stimuli can modify sleep physiology and behavior, yet relatively little is known about the specifics of the wake experiences and their relative contribution to experience-dependent modulation of sleep. Honey bees provide an excellent model system in this regard because their behavioral repertoire is well characterized and the environment they experience during the day can be manipulated while keeping an ecologically and sociobiologically relevant context. We examined whether social experience modulates sleep in honey bees, and evaluated the relative contribution of different social signals. We exposed newly emerged bees to different components of their natural social environment and then monitored their sleep behavior in individual cages in a constant lab environment. We found that rich waking experience modulates subsequent sleep. Bees that experienced the colony environment for 1 or 2 days slept more than same-age sister bees that were caged individually or in small groups in the lab. Furthermore, bees placed in mesh-enclosures in the colony, that prevented direct contact with nestmates, slept similarly to bees freely moving in the colony. These results suggest that social signals that do not require direct or close distance interactions between bees are sufficiently rich to encompass almost the entire effect of the colony on sleep. Our findings provide a remarkable example of social experience-dependent modulation of an essential biological process. [ABSTRACT FROM AUTHOR]

The evolution of advanced sociality in bees is associated with apparent modifications in juvenile hormone (JH) signaling. By contrast to most insects in which JH is a gonadotropin regulating female fertility, in the highly eusocial honey bee (Apis mellifera) JH has lost its gonadotrophic function in adult females, and instead regulates age-related division of labor among worker bees. In order to shed light on the evolution of JH signaling in bees we performed allatectomy and replacement therapies to manipulate JH levels in workers of the "primitively eusocial" bumblebee Bombus terrestris. Allatectomized worker bees showed remarkable reduction in ovarian development, egg laying, Vitellogenin and Krüppel homolog 1 fat body transcript levels, hemolymph Vitellogenin protein abundance, wax secretion, and egg-cell construction. These effects were reverted, at least partially, by treating allatectomized bees with JH-III, the natural JH of bees. Allatectomy also affected the amount of ester component in Dufour's gland secretion, which is thought to convey a social signal relating to worker fertility. These findings provide a strong support for the hypothesis that in contrast to honey bees, JH is a gonadotropin in bumblebees and lend credence to the hypothesis that the evolution of advanced eusociality in honey bees was associated with major modifications in JH signaling. [ABSTRACT FROM AUTHOR]

In many social insects, including bumblebees, the division of labor between workers relates to body size, but little is known about the factors influencing larval development and final size. We confirmed and extend the evidence that in the bumblebee Bombus terrestris the adult bee body size is positively correlated with colony age. We next performed cross-fostering experiments in which eggs were switched between incipient (before worker emergence) and later stage colonies with workers. The introduced eggs developed into adults similar in size to their unrelated nestmates and not to their same-age full sisters developing in their mother colony. Detailed observations revealed that brood tending by the queen decreases, but does not cease, in young colonies with workers. We next showed that both worker number and the queen presence influenced the final size of the developing brood, but only the queen influence was mediated by shortening developmental time. In colonies separated by a queen excluder, brood developmental time was shorter in the queenright compartment. These findings suggest that differences in body size are regulated by the brood interactions with the queen and workers, and not by factors inside the eggs that could vary along with colony development. Finally, we developed a model showing that the typical increase in worker number and the decrease in brood contact with the queen can account for the typical increase in body size. Similar self-organized social regulation of brood development may contribute to the optimization of growth and reproduction in additional social insects. [ABSTRACT FROM AUTHOR]

During the nest-founding phase of the bumble bee colony cycle, queens undergo striking changes in maternal care behavior. Early in the founding phase, prior to the emergence of workers in the nest, queens are reproductive and also provision and feed their offspring. However, later in the founding phase, queens reduce their feeding of larvae and become specialized on reproduction. This transition is synchronized with the emergence of workers in the colony, who assume the task of feeding their siblings. Using a social manipulation experiment with the bumble bee Bombus terrestris, we tested the hypothesis that workers regulate the transition from feeding brood to specialization on reproduction in nest-founding bumble bee queens. Consistent with this hypothesis, we found that early-stage nest-founding queens with workers prematurely added to their nests reduce their brood-feeding behavior and increase egg laying, and likewise, late-stage nest-founding queens increase their brood-feeding behavior and decrease egg-laying when workers are removed from their nests. Further, brood-feeding and egg-laying behaviors were negatively correlated. We used Agilent microarrays designed from B. terrestris brain expressed sequenced tags (ESTs) to explore a second hypothesis, that workers alter brain gene expression in nest-founding queens. We found evidence that brain gene expression in nest-founding queens is altered by the presence of workers, with the effect being much stronger in late-stage founding queens. This study provides new insights into how the transition from feeding brood to specialization on reproduction in queen bumble bees is regulated during the nest initiation phase of the colony cycle. [ABSTRACT FROM AUTHOR]

The circadian clock is a core molecular mechanism that allows organisms to anticipate daily environmental changes and adapt the timing of behaviors to maximize efficiency. In social insects, the ability to maintain the appropriate temporal order is thought to improve colony efficiency and fitness. We used the newly sequenced fire ant (Solenopsis invicta) genome to characterize the first ant circadian clock. Our results reveal that the fire ant clock is similar to the clock of the honeybee, a social insect with an independent evolutionary origin of sociality. Gene trees for the eight core clock genes, period, cycle, clock, cryptochrome-m, timeout, vrille, par domain protein 1 & clockwork orange, show ant species grouping closely with honeybees and Nasonia wasps as an outgroup to the social Hymenoptera. Expression patterns for these genes suggest that the ant clock functions similar to the honeybee clock, with period and cry-m mRNA levels increasing during the night and cycle and clockwork orange mRNAs cycling approximately anti-phase to period. Gene models for five of these genes also parallel honeybee models. In particular, the single ant cryptochrome is an ortholog of the mammalian-type (cry-m), rather than Drosophila-like protein (cry-d). Additionally, we find a conserved VPIFAL C-tail region in clockwork orange shared by insects but absent in vertebrates. Overall, our characterization of the ant clock demonstrates that two social insect lineages, ants and bees, share a similar, mammalian-like circadian clock. This study represents the first characterization of clock genes in an ant and is a key step towards understanding socially-regulated plasticity in circadian rhythms by facilitating comparative studies on the organization of circadian clockwork. [ABSTRACT FROM AUTHOR]

Honey bee (Apis mellifera) workers emerge from the pupae with no circadian rhythms in behavior or brain clock gene expression but show strong rhythms later in life. This postembryonic development of circadian rhythms is reminiscent of that of infants of humans and other primates but contrasts with most insects, which typically emerge from the pupae with strong circadian rhythms. Very little is known about the internal and external factors regulating the ontogeny of circadian rhythms in bees or in other animals. We tested the hypothesis that the environment during early life influences the later expression of circadian rhythms in locomotor activity in young honey bees. We reared newly emerged bees in various social environments, transferred them to individual cages in constant laboratory conditions, and monitored their locomotor activity. We found that the percentage of rhythmic individuals among bees that experienced the colony environment for their first 48 h of adult life was similar to that of older sister foragers, but their rhythms were weaker. Sister bees isolated individually in the laboratory for the same period were significantly less likely to show circadian rhythms in locomotor activity. Bees experiencing the colony environment for only 24 h, or staying for 48 h with 30 same-age sister bees in the laboratory, were similar to bees individually isolated in the laboratory. By contrast, bees that were caged individually or in groups in single- or double-mesh enclosures inside a field colony were as likely to exhibit circadian rhythms as their sisters that were freely moving in the same colony. These findings suggest that the development of the circadian system in young adult honey bees is faster in the colony than in isolation. Direct contact with the queen, workers, or the brood, contact pheromones, and trophallaxis, which are all important means of communication in honey bees, cannot account for the influence of the colony environment, since they were all withheld from the bees in the double-mesh enclosures. Our results suggest that volatile pheromones, the colony microenvironment, or both influence the ontogeny of circadian rhythms in honey bees. [ABSTRACT FROM PUBLISHER]

Following general anesthesia, people are often confused about the time of day and experience sleep disruption and fatigue. It has been hypothesized that these symptoms may be caused by general anesthesia affecting the circadian clock. The circadian clock is fundamental to our well-being because it regulates almost all aspects of our daily biochemistry, physiology, and behavior. Here, we investigated the effects of the most common general anesthetic, isoflurane, on time perception and the circadian clock using the honeybee (Apis mellifera) as a model. A 6-h daytime anesthetic systematically altered the time-compensated sun compass orientation of the bees, with a mean anticlockwise shift in vanishing bearing of 87° in the Southern Hemisphere and a clockwise shift in flight direction of 58° in the Northern Hemisphere. Using the same 6-h anesthetic treatment, time-trained bees showed a delay in the start of foraging of 3.3 h, and whole-hive locomotor-activity rhythms were delayed by an average of 4.3 h. We show that these effects are all attributable to a phase delay in the core molecular clockwork. mRNA oscillations of the central clock genes cryptochrome-m and period were delayed by 4.9 and 4.3 h, respectively. However, this effect is dependent on the time of day of administration, as is common for clock effects, and nighttime anesthesia did not shift the clock. Taken together, our results suggest that general anesthesia during the day causes a persistent and marked shift of the clock effectively inducing "jet lag" and causing impaired time perception. Managing this effect in humans is likely to help expedite postoperative recovery. [ABSTRACT FROM AUTHOR]

Honey bee workers care for (“nurse”) the brood around the clock without circadian rhythmicity, but then they forage outside with strong circadian rhythms and a consolidated nightly rest. This chronobiological plasticity is associated with variation in the expression of the canonical “clock genes” that regulate the circadian clock: nurse bees show no brain rhythms of expression, while foragers do. These results suggest that the circadian system is organized differently in nurses and foragers. Nurses switch to activity with circadian rhythms shortly after being removed from the hive, suggesting that at least some clock cells in their brain continue to measure time while in the hive. We performed a microarray genome-wide survey to determine general patterns of brain gene expression in nurses and foragers sampled around the clock. We found 160 and 541 transcripts that exhibited significant sinusoidal oscillations in nurses and foragers, respectively, with peaks of expression distributed throughout the day in both task groups. Consistent with earlier studies, transcripts of genes involved in circadian rhythms, including Clockwork Orange that has not been studied before in bees, oscillated in foragers but not in nurses. The oscillating transcripts also were enriched for genes involved in the visual system, “development” and “response to stimuli” (foragers), “muscle contraction” and “microfilament motor gene expression” (nurses), and “generation of precursor metabolites” and “energy” (both). Transcripts of genes encoding P450 enzymes oscillated in both nurses and foragers but with a different phase. This study identified new putative clock-controlled genes in the honey bee and suggests that some brain functions show circadian rhythmicity even in nurse bees that are active around the clock. [ABSTRACT FROM PUBLISHER]

Unlike most animals studied so far in which the activity with no circadian rhythms is pathological or linked to deteriorating performance, worker bees and ants naturally care for their sibling brood around the clock with no apparent ill effects. Here, we tested whether bumble-bee queens that care alone for their first batch of offspring are also capable of a similar chronobiological plasticity. We monitored locomotor activity of Bombus terrestris queens at various life cycle stages, and queens for which we manipulated the presence of brood or removed the ovaries. We found that gynes typically emerged from the pupae with no circadian rhythms, but after several days showed robust rhythms that were not affected by mating or diapauses. Colony-founding queens with brood showed attenuated circadian rhythms, irrespective of the presence of ovaries. By contrast, queens that lost their brood switched again to activity with strong circadian rhythms. The discovery that circadian rhythms in bumble-bee queens are regulated by the life cycle and the presence of brood suggests that plasticity in the circadian clock of bees is ancient and related to maternal behaviour or physiology, and is not a derived trait that evolved with the evolution of the worker caste. [ABSTRACT FROM AUTHOR]

Bees provide an excellent model with which to study the neuronal and molecular modifications associated with the evolution of sociality because relatively closely related species differ profoundly in social behaviour, from solitary to highly social. The recent development of powerful genomic tools and resources has set the stage for studying the social behaviour of bees in molecular terms. We review 'ground plan' and 'genetic toolkit' models which hypothesize that discrete pathways or sets of genes that regulate fundamental behavioural and physiological processes in solitary species have been co-opted to regulate complex social behaviours in social species. We further develop these models and propose that these conserved pathways and genes may be incorporated into 'social pathways', which consist of relatively independent modules involved in social signal detection, integration and processing within the nervous and endocrine systems, and subsequent behavioural outputs. Modifications within modules or in their connections result in the evolution of novel behavioural patterns. We describe how the evolution of pheromonal regulation of social pathways may lead to the expression of behaviour under new social contexts, and review plasticity in circadian rhythms as an example for a social pathway with a modular structure. [ABSTRACT FROM AUTHOR]

The honeybee has long been an important model for studying the interplay between the circadian clock and complex behaviors. This article reviews studies further implicating the circadian clock in complex social behaviors in bees. The article starts by introducing honeybee social behavior and sociality and then briefly summarizes current findings on the molecular biology and neuroanatomy of the circadian system of honeybees that point to molecular similarities to the mammalian clockwork rather than to that of Drosophila. Foraging is a social behavior in honeybees that relies on the circadian clock for timing visits to flowers, time-compensated sun-compass navigation, and dance communication used by foragers to recruit nestmates to rewarding flower patches. The circadian clock is also important for the social organization of honeybee societies. Social factors influence the ontogeny of circadian rhythms and are important for social synchronization of worker activities. Both queen and worker bees switch between activities with and without circadian rhythms. In workers this remarkable plasticity is associated with the division of labor; nurse bees care for the brood around the clock with similar levels of clock gene expression throughout the day, whereas foragers have strong behavioral circadian rhythms with oscillating brain clock gene levels. This plasticity in circadian rhythms is regulated by direct contact with the brood and is context-specific in that nurse bees that are removed from the hive exhibit activity with strong behavioral and molecular rhythms. These studies on the sociochronobiology of honeybees and comparative studies with other social insects suggest that the evolution of sociality has influenced the characteristics of the circadian system in honeybees. [ABSTRACT FROM AUTHOR]

The social environment influences the circadian clock of diverse animals, but little is known about the functional significance, the specifics of the social signals, or the dynamics of socially mediated changes in the clock. Honey bees switch between activities with and without circadian rhythms according to their social task. Forager bees have strong circadian rhythms, whereas "nurse" bees typically care for the brood around-the-clock with no circadian rhythms in behavior or clock gene expression. Here we show that nurse-age bees that were restricted to a broodless comb inside or outside the hive showed robust behavioral and molecular circadian rhythms. By contrast, young nurses tended brood with no circadian rhythms in behavior or clock gene expression, even under a light-dark illumination regime or when placed with brood--but no queen--in a small cage outside the hive. This behavior is context-dependent because nurses showed circadian rhythms in locomotor activity shortly after removal from the hive, and in clock gene expression after ~16 h. These findings suggest that direct interaction with the brood modulates the circadian system of honey bees. The dynamics of rhythm development best fit models positing that at least some pacemakers continue to oscillate and be entrained by the environment in nurses that are active around the clock. These cells set the phase to the clock network when the nurse is removed from the hive. These findings suggest that despite its robustness, the circadian system exhibits profound plasticity, enabling adjustment to rapid changes in the social environment. [ABSTRACT FROM AUTHOR]

Although texts and wall paintings suggest that bees were kept in the Ancient Near East for the production of precious wax and honey, archaeological evidence for beekeeping has never been found. The Biblical term "honey" commonly was interpreted as the sweet product of fruits, such as dates and figs. The recent discovery of unfired clay cylinders similar to traditional hives still used in the Near East at the site of Tel Reov in the Jordan valley in northern Israel suggests that a large-scale apiary was located inside the town, dating to the 10th-early 9th centuries B.C.E. This paper reports the discovery of remains of honeybee workers, drones, pupae, and larvae inside these hives. The exceptional preservation of these remains provides unequivocal identification of the clay cylinders as the most ancient beehives yet found. Morphometric analyses indicate that these bees differ from the local subspecies Apis mellifera syriaca and from all subspecies other than A. m. anatoliaca, which presently resides in parts of Turkey. This finding suggests either that the Western honeybee subspecies distribution has undergone rapid change during the last 3,000 years or that the ancient inhabitants of Tel Reov imported bees superior to the local bees in terms of their milder temper and improved honey yield. [ABSTRACT FROM AUTHOR]

Background: Regulation of worker behavior by dominant queens or workers is a hallmark of insect societies, but the underlying molecular mechanisms and their evolutionary conservation are not well understood. Honey bee and bumble bee colonies consist of a single reproductive queen and facultatively sterile workers. The queens' influences on the workers are mediated largely via inhibition of juvenile hormone titers, which affect division of labor in honey bees and worker reproduction in bumble bees. Studies in honey bees identified a transcription factor, Krüppel-homolog 1 (Krh1), whose expression in worker brains is significantly downregulated in the presence of a queen or queen pheromone and higher in forager bees, making this gene an ideal candidate for examining the evolutionary conservation of socially regulated pathways in Hymenoptera. Results: In contrast to honey bees, bumble bees foragers do not have higher Kr-h1 levels relative to nurses: in one of three colonies levels were similar in nurses and foragers, and in two colonies levels were higher in nurses. Similarly to honey bees, brain Kr-h1 levels were significantly downregulated in the presence versus absence of a queen. Furthermore, in small queenless groups, Kr-h1 levels were downregulated in subordinate workers with undeveloped ovaries relative to dominant individuals with active ovaries. Brain Kr-h1 levels were upregulated by juvenile hormone treatment relative to a vehicle control. Finally, phylogenetic analysis indicates that KR-H1 orthologs are presence across insect orders. Though this protein is highly conserved between honey bees and bumble bees, there are significant differences between orthologs of insects from different orders. Conclusions: Our results suggest that Kr-h1 is associated with juvenile hormone mediated regulation of reproduction in bumble bees. The expression of this transcription factor is inhibited by the queen and associated with endocrine mediated regulation of social organization in two species of bees. Thus, KR-H1 may transcriptionally regulate a conserved genetic module that is part of a pathway that has been co-opted to function in social behavior, and adjusts the behavior of workers to their social environmental context. [ABSTRACT FROM AUTHOR]

Honeybee (Apis mellifera) foragers are among the first invertebrates for which sleep behavior has been described. Foragers (typically older than 21 days) have strong circadian rhythms; they are active during the day, and sleep during the night. We explored whether young bees (∼3 days of age), which are typically active around-the-clock with no circadian rhythms, also exhibit sleep behavior. We combined 24-hour video recordings, detailed behavioral observations, and analyses of response thresholds to a light pulse for individually housed bees in various arousal states. We characterized three sleep stages in foragers on the basis of differences in body posture, bout duration, antennae movements and response threshold. Young bees exhibited sleep behavior consisting of the same three stages as observed in foragers. Sleep was interrupted by brief awakenings, which were as frequent in young bees as in foragers. Beyond these similarities, we found differences in the sleep architecture of young bees and foragers. Young bees passed more frequently between the three sleep stages, and stayed longer in the lightest sleep stage than foragers. These differences in sleep architecture may represent developmental and/or environmentally induced variations In the neuronal network underlying sleep in honeybees. To the best of our knowledge, this is the first evidence for plasticity in sleep behavior in insects. [ABSTRACT FROM AUTHOR]

Various animals naturally switch to considerable periods of around-the-clock activity with no apparent ill effects. Such plasticity in overt circadian rhythms might be observed because the clock is masked by the influence of external factors, is uncoupled from behavioral outputs, or results from genuine plasticity in the clock machinery. We studied honeybees in which plasticity in circadian rhythms is socially modulated and associated with the division of labor. We confirm that "nurse" bees care for the brood around-the-clock even when experiencing a light:dark illumination regime. However, nurses transferred from the hive to individual cages in constant conditions have robust circadian rhythms in locomotor activity with an onset of activity at the subjective morning. These data indicate that circadian rhythmicity in nurses depends on their environment, and suggest that some clockwork components were entrained even in nurses active around the clock while in the hive. Brain oscillations in transcript abundance for the putative clock genes Period, Cryptochrome-m, Cycle, and Timeout were attenuated or totally suppressed in nurses as compared to behaviorally rhythmic foragers, irrespective of the illumination regime. These findings provide the first support for the hypothesis that natural plasticity in circadian rhythms is associated with reorganization of the internal clockwork. [ABSTRACT FROM AUTHOR]

Octopamine (OA) and juvenile hormone (JH) are implicated in the regulation of age-based division of labor in the honeybee, Apis mellifera. We tested the hypothesis that these two neuroendocrine signals influence task-associated plasticity in circadian and diurnal rhythms, and in brain expression of the clock gene period ( per). Treatment with OA, OA antagonist (epinastine), or both, did not affect the age at onset of circadian rhythmicity or the free running period in constant darkness (DD). Young bees orally treated with OA in light–dark (LD) illumination regime for 6 days followed by DD showed reduced alpha (the period between the daily onset and offset of activity) during the first 4 days in LD and the first 4 days in DD. Oral treatment with OA, epinastine, or both, but not manipulations of JH levels, caused increased average daily levels and aberrant patterns of brain per mRNA oscillation in young bees. These results suggest that OA and JH do not influence the development or function of the central pacemaker but rather that OA influences the brain expression of a clock gene and characteristics of locomotor behavior that are not thought to be under direct control of the circadian pacemaker. [ABSTRACT FROM AUTHOR]

We investigated labor-related plasticity in the circadian clock of the bumblebee Bombus terrestris. Bumblebee workers vary enormously in body size, and we found that size, division of labor, and diurnal rhythms in activity are correlated in B. terrestris colonies. Large workers typically perform foraging activities with strong diurnal rhythms and low activity at night, whereas small bees typically care for (nurse) brood around the clock with weak or no diurnal rhythms. Under constant laboratory conditions, circadian rhythms in locomotor activity were weaker, less stable, and developed at a later age in small (nurse-size) bees compared to their larger (forager-size) sisters. Under a light:dark illumination regime, many small bees, particularly at a young age, were active during the dark phase, fewer small bees developed rhythms, and they did so later compared to large bees. Taken together these findings reveal naturally occurring attenuation or suppression in the circadian clock of small bees that is determined during pre-adult development. This deficiency in clock function, however, does not result in pathology but rather appears to be functionally significant, because it is associated with around-the-clock brood care activity and therefore apparently improves divisions of labor and colony efficiency. This in turn suggests that variation in social biology influences traits of the circadian clock. [ABSTRACT FROM AUTHOR]

Abstract Young adult honey bees work inside the beehive "nursing" brood around the clock with no circadian rhythms; older bees forage for nectar and pollen outside with strong circadian rhythms. Previous research has shown that the development of an endogenous rhythm of activity is also seen in the laboratory in a constant environment. Newly emerging bees maintained in isolation are typically arrhythmic during the first few days of adult life and develop strong circadian rhythms by about a few days of age. In addition, average daily levels of period (per) mRNA in the brain are higher in foragers or forager-age bees (> 21 days of age) relative to young nest bees (is similar to 7 days of age). The authors used social manipulations to uncouple behavioral rhythmicity, age, and task to determine the relationship between these factors and per. There was no obligate link between average daily levels of per brain mRNA and either behavioral rhythmicity or age. There also were no differences in per brain mRNA levels between nurse bees and foragers in social environments that promote precocious or reversed behavioral development. Nurses and other hive-age bees can have high or low levels of per mRNA levels in the brain, depending on the social environment, while foragers and foraging-age bees always have high levels. These findings suggest a link between honey bee foraging behavior and per up-regulation. Results also suggest task-related differences in the amplitude of per mRNA oscillation in the brain, with foragers having larger diurnal fluctuation in per than nurses, regardless of age. Taken together, these results suggest that social factors may exert potent influences on the regulation of clock genes. [ABSTRACT FROM AUTHOR]

Discusses a study which reported the changes in per messenger RNA (mRNA) levels in the brain associated with division of labor in honey bee colonies. Materials and methods of the study; Results; Discussion of the results.

Simple Summary: In diverse animal species, individuals establish dominance hierarchies by means of agonistic interactions. Dominance rank is functionally significant because it affects access to vital resources such as mates, food, and shelter, but little is known on the underlying genetic and molecular mechanisms, specifically in insects, and among females. We tested the hypothesis that Krüppel homologue 1, a key endocrine signaling gene, influences dominance among bumble bee female workers. We developed and validated a new nanoparticle-based protocol to down-regulate gene expression in bumble bees. Using this protocol, we show that Krüppel homologue 1 mediates endocrine influences, not only on fertility and wax production, but also on aggression and dominance rank. These findings, which establish the first causal link between a gene and a dominance rank in a social insect, are important for determining whether there are general molecular principles governing dominance ranks across gender and animal species. Dominance hierarchies are ubiquitous in invertebrates and vertebrates, but little is known on how genes influence dominance rank. Our gaps in knowledge are specifically significant concerning female hierarchies, particularly in insects. To start filling these gaps, we studied the social bumble bee Bombus terrestris, in which social hierarchies among females are common and functionally significant. Dominance rank in this bee is influenced by multiple factors, including juvenile hormone (JH) that is a major gonadotropin in this species. We tested the hypothesis that the JH responsive transcription factor Krüppel homologue 1 (Kr-h1) mediates hormonal influences on dominance behavior. We first developed and validated a perfluorocarbon nanoparticles-based RNA interference protocol for knocking down Kr-h1 expression. We then used this procedure to show that Kr-h1 mediates the influence of JH, not only on oogenesis and wax production, but also on aggression and dominance rank. To the best of our knowledge, this is the first study causally linking a gene to dominance rank in social insects, and one of only a few such studies on insects or on female hierarchies. These findings are important for determining whether there are general molecular principles governing dominance rank across gender and taxa. [ABSTRACT FROM AUTHOR]

Possible pheromonal control of worker reproduction was tested in Bombus terrestris. The mode of assay included exposure of callow workers to extracts originating from different queen parts and measuring the effect on the in vitro biosynthesis of juvenile hormone (JH), the apparent gonadotropin in this species. Both queen total body extracts applied to dummies consisting of oven-dried or Soxhlet-washed virgin queen bodies and cuticular washes applied to living virgin queens effectively inhibited the biosynthesis of JH in callow workers. None of the five exocrine glands (mandibular, hypopharyngeal, salivary, Dufour's, and tarsal) demonstrated inhibitory activity. Likewise, the use of synthetic 3-hydroxy acids, found in queen mandibular glands, were ineffective in blocking JH biosynthesis in queenless workers. The results suggest that the queen may use a primer pheromone spread on the epicuticle as a means to inhibit worker reproduction. However, our results are not consistent with the prevailing hypothesis that in B. terrestris the main source of the pheromone that inhibits worker reproduction is in the queen's mandibular glands. [ABSTRACT FROM AUTHOR]

The mechanisms of regulating worker reproduction in bumblebees were studied by direct behavioral observations and by measuring ovarian development and juvenile hormone (JH) biosynthesis rates in workers under different social conditions. Workers in the last stage of Bombus terrestris colony development (the competition phase) had the lowest ovarian development and JH biosynthesis rates. Callows introduced into colonies immediately after queen removal (dequeened colonies) demonstrated a significant increase in ovarian development before, but not during, the competition phase. These findings differ from the higher ovarian development in colonies during the competition phase predicted by the prevailing hypothesis that worker reproduction starts in response to a decrease in queen inhibition. Reproduction of callows housed with dominant workers in small queenless groups was inhibited as in queenright colonies. This suggests that the reduced ovarian development and JH biosynthesis rates observed in dequeened and normally developing colonies during the competition phase also reflect inhibition by dominant workers. Thus, two distinct stages of inhibition of reproduction seem to exist: (1) before the competition phase, when the queen slows down worker ovarian development and prevents oviposition; (2) during the competition phase, when dominant workers inhibit ovarian development of other workers. Between these stages there seems to be a temporal “window” of enhanced worker reproductive development. The queen's typical switch to haploid egg production was not associated with changes in worker ovarian development or JH biosynthesis rates. These findings suggest that regulation of worker reproduction in B. terrestris is not determined by simple changes in the queen's inhibition capacity or by the sex of offspring and that the worker's role is more important than previously believed. [ABSTRACT FROM AUTHOR]

Simple Summary: Behavioural specialisation of individuals may improve the performance of groups, but could also limit the ability to switch tasks (behavioural 'plasticity') in response to changing group needs. In bumble bee colonies, body size, which is fixed once the bees reach adulthood, influences the tasks that bees perform, meaning that large and small bees often act as specialists. We found that when we experimentally reduced the body-size variation of colonies, some performed less well than normal. Nonetheless, in other colonies, individuals increased task specialisation or effort, which apparently compensated for the absence of large and small workers. These results suggest that both behavioural specialisation and plasticity can be important in collective group performance. Specialisation and plasticity are important for many forms of collective behaviour, but the interplay between these factors is little understood. In insect societies, workers are often developmentally primed to specialise in different tasks, sometimes with morphological or physiological adaptations, facilitating a division of labour. Workers may also plastically switch between tasks or vary their effort. The degree to which developmentally primed specialisation limits plasticity is not clear and has not been systematically tested in ecologically relevant contexts. We addressed this question in 20 free-foraging bumble bee (Bombus terrestris) colonies by continually manipulating colonies to contain either a typically diverse, or a reduced ("homogeneous"), worker body size distribution while keeping the same mean body size, over two trials. Pooling both trials, diverse colonies produced a larger comb mass, an index of colony performance. The link between body size and task was further corroborated by the finding that foragers were larger than nurses even in homogeneous colonies with a very narrow body size range. However, the overall effect of size diversity stemmed mostly from one trial. In the other trial, homogeneous and diverse colonies showed comparable performance. By comparing behavioural profiles based on several thousand observations of individuals, we found evidence that workers in homogeneous colonies in this trial rescued colony performance by plastically increasing behavioural specialisation and/or individual effort, compared to same-sized individuals in diverse colonies. Our results are consistent with a benefit to colonies of large and small specialists under certain conditions, but also suggest that plasticity or effort can compensate for reduced (size-related) specialisation. Thus, we suggest that an intricate interplay between specialisation and plasticity is functionally adaptive in bumble bee colonies. [ABSTRACT FROM AUTHOR]

Colonies of the bumblebee Bombus terrestris are characterized by wide phenotypic variability among genetically similar full-sister workers, suggesting a major role for epigenetic processes. Here, we report a high level of ADAR-mediated RNA editing in the bumblebee, despite the lack of an ADAR1-homolog. We identify 1.15 million unique genomic sites, and 164 recoding sites residing in 100 protein coding genes, including ion channels, transporters, and receptors predicted to affect brain function and behavior. Some edited sites are similarly edited in other insects, cephalopods and even mammals. The global editing level of protein coding and non-coding transcripts weakly correlates with task performance (brood care vs. foraging), but not affected by dominance rank or juvenile hormone known to influence physiology and behavior. Taken together, our findings show that brain editing levels are high in naturally behaving bees, and may be regulated by relatively short-term effects associated with brood care or foraging activities. Bumblebee workers are genetically highly similar but they show different behaviors such as brood care and foraging. Here the authors report a high level of ADAR-mediated RNA editing in the bumblebee Bombus terrestris and its weak correlation to task performance. [ABSTRACT FROM AUTHOR]

Several related and complementary theoretical frameworks have been proposed to explain the existence of prosocial behavior, despite its potential fitness cost to the individual. These include kin selection theory, proposing that organisms have a propensity to help those to whom they are genetically related, and reciprocity, referring to the benefit of being prosocial, depending on past and future mutual interactions. A useful paradigm to examine prosociality is to compare mean levels of this behavior between monozygotic (MZ) and dizygotic (DZ) twins. Here, we examined the performance of 883 6.5‐year‐old twins (139 MZ and 302 DZ same‐sex 6.5‐year‐old full twin pairs) in the Differential Productivity Task. In this task, the twins' behaviors were observed under two conditions: working for themselves vs. working for their co‐twin. There were no significant differences between the performances of MZ and DZ twins in the prosocial condition of the task. Correlations within the twin dyads were significantly higher in MZ than DZ twins in the self‐interested condition. However, similar MZ and DZ correlations were found in the prosocial condition, supporting the role of reciprocity in twins' prosociality towards each other. No significant differences were found in Monozygotic (MZ) and Dizygotic (DZ) prosocial behavior towards their co‐twin, despite MZ twins being closer genetically than DZ twins. Further analyses of twin correlations showed that while MZ twins were more strongly correlated than DZ twins in the self‐interested condition of the Differential Productivity Task, MZ and DZ twin dyads were similar in the prosocial condition, supporting the role of reciprocity in twins' prosociality towards each other. [ABSTRACT FROM AUTHOR]