New meta-analysis tools reveal common transcriptional regulatory basis for multiple determinants of behavior.

A fundamental problem in meta-analysis is how to systematically combine information from multiple statistical tests to rigorously evaluate a single overarching hypothesis. This problem occurs in systems biology when attempting to map genomic attributes to complex phenotypes such as behavior. Behavior and other complex phenotypes are influenced by intrinsic and environmental determinants that act on the transcriptome, but little is known about how these determinants interact at the molecular level. We developed an informatic technique that identifies statistically significant meta-associations between gene expression patterns and transcription factor combinations. Deploying this technique for brain transcriptome profiles from ca. 400 individual bees, we show that diverse determinants of behavior rely on shared combinations of transcription factors. These relationships were revealed only when we considered complex and variable regulatory rules, suggesting that these shared transcription factors are used in distinct ways by different determinants. This regulatory code would have been missed by traditional gene coexpression or cis-regulatory analytic methods. We expect that our meta-analysis tools will be useful for a broad array of problems in systems biology and other fields.

Honey bee aggression supports a link between gene regulation and behavioral evolution.

A prominent theory states that animal phenotypes arise by evolutionary changes in gene regulation, but the extent to which this theory holds true for behavioral evolution is not known. Because "nature and nurture" are now understood to involve hereditary and environmental influences on gene expression, we studied whether environmental influences on a behavioral phenotype, i.e., aggression, could have evolved into inherited differences via changes in gene expression. Here, with microarray analysis of honey bees, we show that aggression-related genes with inherited patterns of brain expression are also environmentally regulated. There were expression differences in the brain for hundreds of genes between the highly aggressive Africanized honey bee compared with European honey bee (EHB) subspecies. Similar results were obtained for EHB in response to exposure to alarm pheromone (which provokes aggression) and when comparing old and young bees (aggressive tendencies increase with age). There was significant overlap of the gene lists generated from these three microarray experiments. Moreover, there was statistical enrichment of several of the same cis regulatory motifs in promoters of genes on all three gene lists. Aggression shows a remarkably robust brain molecular signature regardless of whether it occurs because of inherited, age-related, or environmental (social) factors. It appears that one element in the evolution of different degrees of aggressive behavior in honey bees involved changes in regulation of genes that mediate the response to alarm pheromone.

Genotype, task specialization, and nest environment influence the stinging response thresholds of individual Africanized and European honeybees to electrical stimulation.

This study was conducted to analyze the stinging response thresholds of individual European and Africanized worker honeybees (Apis mellifera L.) to electrical stimulation. Newly emerged workers were identified, and either were placed into an incubator, into their natal colonies, or cross-fostered in common colonies of European or Africanized ancestry. Nest and guard bees of each type were collected and exposed to an electric stimulus of 0.5 mA, and the time they took to sting a leather substrate was recorded. Africanized bees consistently had significant lower thresholds of defensive response than European bees across all of the environments tested. Guards were faster to sting than nest bees only for the Africanized genotype, suggesting that alleles of African origin have pleiotropic effects on guarding and stinging. This is the first study that shows that single individuals specialized in guarding also may have a lower response threshold for stinging. Environmental effects were also evident. In all cases, bees responded faster to the electrical stimulation after being kept in environments other than their natal nest. Moreover, significant genotype by environment and genotype by task specialization interactions were found. Our results fit a model of division of labor based on differences in response thresholds to stimuli among workers of different genotypes and task groups that result in non-additive effects on colony behavior.