Size-dependent foraging gene expression and behavioral caste differentiation in Bombus ignitus

A putative open reading frame of the Bifor gene was 2004 bp in length. It encoded 668 aa residues and showed high identity to orthologous genes in other hymenopterans (85.3-99.0%). As in ants and wasps, Bifor expression levels were higher in nurses than in foragers. Bifor expression was negatively correlated with individual body size even within the same behavioral castes (regression coefficient = -0.376, P < 0.001, all individuals; -0.379, P = 0.018, within foragers).These findings indicate that Bifor expression is size dependent and support the idea that Bifor expression levels are related to behavioral caste differentiation in B. ignitus. Thus, the relationship between foraging gene expression and behavioral caste differentiation found in ants and wasps was identified in a different system of labor determination.Animal foraging behavior is a particularly interesting phenomenon from both ecological and evolutionary perspectives [1,2]. Although understanding the genetic basis of individual foraging behavior is important for evolutionary studies, in most case the genes controlling this behavior have not been identified. Candidate genes have, nevertheless, been identified in insects, and genetic analyses of behavioral differences have been conducted. For example, a foraging gene in the fruit fly (Drosophila melanogaster) differentiates behavior via a two-allele system: individuals with an R allele (rovers) show higher activity for food materials than those with a for allele (sitters; [3]). The same locus is also related to sucrose response, resistance to high temperature, and learning [4-6].Foraging genes, members of the cGMP-dependent protein kinase (PKG) family, are also found in social insects and are related to the division of labor through behavioral caste differentiation in colonies. In honeybees (Apis mellifera), foraging gene (Amfor) activity differs according to worker age, with gene expression levels increasing with increasing age. Young workers with low ex