Molecular Determinants of Scouting Behavior in Honey Bees

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Science  09 Mar 2012:
Vol. 335, Issue 6073, pp. 1225-1228
DOI: 10.1126/science.1213962

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  1. Fig. 1

    (A) Consistent novelty-seeking behavior across different contexts. Nest scouts were significantly more likely to later act as food scouts than were non-scout swarm members. The graph shows the probabilities of food scouting for nine trials: four natural swarms and five artificial swarms, with eight different colonies (Fisher’s exact test, 2-tailed test; *P < 0.05, **P < 0.01, ***P < 0.001), and the overall mean probabilities [least-square means and standard errors; mixed-model analysis of variance (ANOVA), 2-tailed test]. (B) Feeder-discovery assay for identifying food scouts. Additional details are in the text and supporting online material.

  2. Fig. 2

    Transcriptomic analyses of individual differences in novelty-seeking between food scouts (S) and non-scouts (NS) (n = 20 bees per group). (A) Selected microarray results highlight differences in brain expression for 10 dopamine, octopamine, glutamate, or GABA signaling genes related to novelty seeking, motivation, and reward in vertebrates. DopR2 and OctR1 did not show significant differences in expression (in the latter case, probably because of very low expression levels). GABA transporter 1A gene (Gat-a) expression was one of the best correlates of scouting behavior (permutation t test, P < 0.05). (B) Results of LDA for genes shown in (A) demonstrate clear separation between most scouts and non-scouts based on differences in brain gene expression (standardized expression values: mean = 0, SD = 1). This plot of LD1 versus LD2 accounted for 82% of the variation in brain gene expression across scouts and non-scouts (n = 20 bees per group). S1, S2, S3 and N1, N2, N3: scouts and non-scouts, respectively, from three different colonies.

  3. Fig. 3

    Glutamate or octopamine treatment increased the probability of scouting, whereas dopamine antagonist treatment decreased it (*P < 0.05, ***P < 0.0001). (A) Oral administration of MSG to non-scouts in sugar syrup (20 mg/ml) caused a significant effect in 7 out of 12 trials (with 11 colonies) over 2 years, an overall 73% increase in scouting probability as compared to sucrose-fed–only control bees (P < 0.0001, mixed-model ANOVA, 2-tailed test). Octopamine (OA) treatment (4 mg/ml) caused a significant effect in 3 out of 10 trials (in nine colonies) over 2 years, an overall 37% increase in scouting probability (P < 0.05). Statistical tests were performed on square root–transformed data; the graph represents the untransformed mean ± SE of 12 trials for MSG (with 11 colonies) and 10 trials for octopamine (with 9 colonies); results of individual trials are shown in figs. S3 and S4. (B) The glutamate vesicular transporter blocker Chicago Sky Blue (CSB) (4 mg/ml) blocked the effect of MSG on scouting (P < 0.05, least-square mean ± SE for four previously MSG-responsive colonies; results of individual trials are shown in fig. S3). (C) Non-scout foragers treated with dopamine antagonists (DAA) (either the D1-receptor antagonist SCH-23390, the “pan-receptor” antagonist Flupenthixol, or both) showed an overall 44% decrease in scouting probability in seven trials over three colonies (P < 0.05, the graph represents least-square mean ± estimated error; mixed-model ANOVA, 2-tailed test; results of individual trials are shown in fig. S5). The probability of scouting was calculated from the proportion of foragers in each treatment group that exhibited scouting behavior, based on a precise count of foragers when releasing them from treatment cages.