Behavior and the limits of genomic plasticity: power and replicability in microarray analysis of honeybee brains

Transcription is slow relative to many post-transcriptional processes in the brain. Using the rich system of division of labor in the honeybee (Apis mellifera), we found extreme differences in the extent to which behavioral occupations of different durations were associated with gene-expression differences in the brain. Nursing and foraging, occupations lasting > 1 week, were associated with significant expression differences for nearly one-quarter of the genes tested (1208 of 5563 cDNAs tested; P < 0.01, ANOVA), consistent with previous results. In contrast, transitional occupations, performed for 1-2days after nursing and before the onset of foraging, were associated with either no differences (guards vs. undertakers; 19 cDNAs, fewer than the expectation of 56 false-positives) or few differences (comb builders vs. guards and undertakers; 248 cDNAs), but extensive differences relative to both nursing and foraging (> 500 cDNAs, all contrasts). Statistical power analysis indicated that expression differences of two-, 1.5- and 1.25-fold should have been detected in 100, 92 and 37% of cases, respectively. Replication of previous results at these magnitudes was 95, 71 and 51%, with no genes showing differences in the opposite direction. These results indicate that behavioral plasticity over different time-scales may be associated with substantial differences in the extent of genomic plasticity in the brain.