Genetics of Social Behavior - Sociogenomics - Eusociality - Honey Bee

Honey Bee

To examine higher insect social order, researchers looked into the potential evolutionary history of a “foraging gene” in honey bees (Apis mellifera). Honey bees have a several week lifespan divided between two phases—one spent caring for the hive, the other spent foraging. The regulation of social foraging is important to maintain division of labor, requisite of eusocial organization. In order to discover how foraging is bees is genetically encoded, the honey bee genome was searched for genes that may be shared by other species. A molecular basis for feeding behavior has been determined in Drosophila melanogaster, which shares a common insect ancestor. The “foraging gene” in D. melanogaster encodes a cGMP mediated protein kinase (PKG). Naturally occurring allelic variation produces behavioral syndromes in D. melanogaster, both “sitters” and “rovers”. The needs of a honey bee colony are communicated between bees by pheromones, chemical signals which trigger behavioral responses. Honey bees have a variant of the same foraging gene that controls the onset of foraging behavior. Elevated expression of this gene correlates with increased foraging activity; precocious foraging was induced in young workers by experimentally introducing PKG.

Further clues to the genetic origins of eusociality have been derived by comparing quality of genomic processes. Also applying to A. mellifera; by looking at the degree of genetic linkage and chromosomal recombination rates, light may be shed on the consequence of group selection on a eusocial insect colony. Within the Order Hymenoptera, primitively and highly eusocial species tend to have greater gene linkage and significantly higher more DNA recombination events than non-social species. This trend continues within groups of eusocial species, highly eusocial species have highly recombinant genomes. While contested, recombination activity might originate from the influence of group selection acting on developing eusocial organization in haplodiploids, where colonies that can best maintain a stable coefficient of relatedness are favored.

An early study also determined the cellular basis of the discrete caste morphology of A. mellifera. Queens arise when workers in a colony selectively feed chosen larvae royal jelly. The caste differentiation occurs through an epigenetic process; non-heritable factors contributing to gene expression. Queen and worker morphological forms both come occur from the same genome, royal jelly nourishment is the non-genetic determiner. The pathway to queen morphs is through increased mRNA translation in the cytosol. Biogenesis of organelles occurs at the same rate in both types of larvae, as evidenced by the ratio of mitochondrial DNA to nuclear DNA. Special feeding leads to an increase of metabolic rate for larval queen to facilitate the energy requirement to develop their larger body size.