"Honey bees are among the first invertebrates for which sleep behavior has been described (Kaiser and Steiner-Kaiser 1983). Honey bee foragers exhibit sleep, both in their natural hive environment, and when isolated individually in the lab. Foragers sleep in a posture characterized by a relaxation of the thorax, head, and antennae. This characteristic posture is associated with a decrease in muscle tonus and body temperature, and an increase in response threshold, measured both neurophysiologi-callyand behaviorally (Kaiser and Steiner-Kaiser 1983; Kaiser 1988). It was further suggested that deep sleep in foragers (determined as periods lacking antennal movements) is correlated with rhythmic electrophysiological activity in the brain, including themushroom bodies (Schuppe 1995). Foragers deprived of sleep for 12 hours showed a rebound the next day; they increased the duration of antennal immobility, one of the characteristics of sleep in bees (Sauer et al. 2004). This suggests that sleep in foragers is homeostatically regulated. Foragers are relatively old workers, have strong circadian rhythms, and sleep during the night. However, circadian rhythms are not typical to all worker bees; young bees typically perform various in-hive activities around-the-clock, with no circadian rhythms (Crailsheim et al. 1996; Moore et al. 1998). Young bees that are isolated individually, or kept in small groups in constant conditions, have no circadian rhythms in locomotor activity during their first 3-14 days (Moore 2001; Meshi and Bloch 2007). Their around-the-clock pattern of activity raises the question of whether young bees sleep as foragers do. It is possible that young honey bees do not sleep at all, which would make them an exception in the animal kingdom. An alternative hypothesis is that young bees do sleep like foragers, but distribute their sleep throughout the day. A third hypothesis is that young bees sleep, but their sleep is essentially different from that of foragers. In order to distinguish between these hypotheses, Eban-Rothschild and Bloch (2008) characterized the sleep behavior of individually isolated young bees, and compared it to that of sister foragers. Their detailed behavioral observations and analyses of response thresholds lend weight to the third hypothesis. They showed that young honey bees exhibit sleep behavior which is composed of the same stages observed in foragers, but their sleep dynamics differ (Eban-Rothschild and Bloch 2008)."
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