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First published online July 14, 2008
Journal of Experimental Biology 211, 2408-2416 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.016915
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Differences in the sleep architecture of forager and young honeybees (Apis mellifera)

Ada D. Eban-Rothschild and Guy Bloch*

Department of Evolution, Systematics, and Ecology, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel


Figure 1
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  		Fig. 1. Body posture of honeybee workers in various arousal states. Each photograph is a single frame taken from continuous 24 h video recordings. (A) Immobile–active state (IA) – the bee stays in the same place, the thorax, abdomen and head are clearly raised above the substrate. This bee is moving her wings. (B) First sleep stage (FS) – the abdomen and thorax are clearly raised above the substrate, and the antennae are extended at an angle of 90–180° between the pedicle and the scape. (C) Second sleep stage (SS) – the body is typically more adjacent to the substrate, and the antennae are extended at an angle of ~90° between the pedicle and the scape. (D) Third sleep stage (TS) – the muscle tonus is reduced, and the body is adjacent to the substrate. The angle between the pedicle and scape <90°, with the antennae tips typically touching the substrate. For more details, see Table 1.

 

Figure 2
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  		Fig. 2. Ethological characterization of sleep stages in honeybees. (A) Bout duration at different sleep stages (mean ± s.e.m.), for a representative forager. Similar results were obtained for 15 additional foragers (N=21–194 bouts/bee). (B) Antennae movements at different sleep stages (mean ± s.e.m.), for a representative forager. Similar results were obtained for 16 additional foragers (N=131–906 min/bee). Different capital letters indicate statistically significant differences. (C) Group summary of antennae movement data for all foragers and callows. There was no significant difference between foragers and callows (see supplementary material Table S1). (D) Summary of bout duration data for all foragers and callows. Bout duration differed between foragers and callows (see supplementary material Table S2). Numbers within or above bars are the sample sizes. Filled bars, foragers; open bars, callows; left panels, colony H3; middle panels, colony H12; right panels, colony S25. FS, first sleep stage; SS, second sleep stage; TS, third sleep stage.

 

Figure 3
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  		Fig. 3. Response threshold of bees in different arousal states. (A) Foragers. (B) Callows. Right panels: colony H23; left panels: colony S25. The response threshold to a light pulse differed significantly across arousal states, but not between callows and foragers. The central horizontal line in each box indicates the median, the box borders indicate the 75th and 25th percentile, and the error bars outline the range. Circles indicate outliers; values in a range spanning between 1.5 and 3 box lengths. Asterisks indicate extreme values: values in a range spanning more than three box lengths. Sample size (number of bees) is shown within or above each box. Different capital letters indicate arousal states that are statistically different (Kruskal–Wallis tests followed by multiple comparisons, P<0.0001 for both foragers and callows). FS, first sleep stage; SS, second sleep stage; TS, third sleep stage. Response threshold, at TS, was not determined for foragers in colony S23.

 

Figure 4
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  		Fig. 4. Transitions between behavioral states throughout the day. (A) An example of a forager. (B) An example of a callow with apparent around-the-clock activity. (C) An example of a callow with apparent circadian rhythm in activity. The three bees are from colony H3. Note that the two callow bees manifested all three sleep stages. A, active; IA/G, immobile–active or grooming; FS, first sleep stage; SS, second sleep stage; TS, third sleep stage. For details on behavioral states see Fig. 1 and Table 1. Gray background indicates sleep stages; white background indicates awake states. The horizontal bars at the bottom of the plots depict the subjective time: black bars, subjective night; hatched bars, subjective day. (D) Sleep bout duration (mean ± s.e.m.). Bout duration differed between foragers and callows (two-way ANOVA, age effect, P=0.04) (E) Number of sleep bouts per day (mean ± s.e.m.). The number of sleep bouts differed between foragers and callows (two-way ANOVA, P=0.016). Numbers within boxes indicate the sample size (pooled from the three colonies). Filled bars, foragers; open bars, callows. Asterisks indicate a statistically significant difference between foragers and callows.

 

Figure 5
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  		Fig. 5. The dynamics of transitions between behavioral states. Schematic representation of average transition matrix for foragers (A), and callows (B). The width of arrows is proportional to the average probabilities of transitions from each behavioral state to all other states. The patterns are analyzed from a first-order Markov chain (see Materials and methods), by using 3127 and 3928 behavioral transitions, from 16 foragers and 17 callows, respectively (pooled from colonies H3, H12 and S25). The overall matrices of callows and foragers differ from each other (LOOCV analysis, P=0.002; supplementary material Fig. S1). Transitions that are statistically significantly different between callows and foragers are highlighted in black. For clarity, we show only transitions with average probability >0.1. See Fig. 1 and Table 1 for more details on behavioral states. (C) The difference between average transition probability of foragers and callows. {Delta}Pr=the probability matrix of foragers subtracted from that of callows. Blue colors represent transitions that are more frequent in foragers; red colors represent transitions that are more frequent in callows (see scale).

 

Figure 6
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  		Fig. 6. Transitions between arousal states. (A) Number of sleep–wake transitions during the day. (B) Number of transitions between sleep stages during a single sleep bout. Numbers within boxes indicate the sample size. Filled bars, foragers; open bars, callows. Asterisks indicate a statistically significant difference between foragers and callows.

 

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© The Company of Biologists Ltd 2008