For the first time scientists have been able to examine the genetic processes that decide whether a juvenile bee is destined for life as a worker or as a queen. By stringing together a series of images that describe which genes are active, researchers at the Bee Research Laboratory, Maryland, and the University of Arizona have been able to picture exactly how hormones triggered by environmental and nutritional influences cause larvae to activate the genes necessary to fulfil their destiny.
Female honeybees, Apis mellifera, begin life as bipotential larva with the capability to develop into one of two castes, either worker or queen. The ability of young from the same species to differentiate into different castes is known as polyphenism, says Dr Jay Evans from the Bee Research Laboratory in a new research article due to be published in the January issue of Genome Biology next week. This is the first genomic-scale view of such polyphenic development, he continues.
The researchers used gene-expression profiles, known as arrays, to establish exactly which genes were active as the larvae developed. From the outset, the team found that those larvae destined to become queen bees appeared to down-regulate some of the genes characteristic of bipotential larva and switch on a distinct set of caste-related genes, including genes responsible for metabolism and respiration. Worker bees, they found, continued to express more of the genes typical of the juvenile larva. This difference in gene expression is thought to lead to a difference in the size and function of organs that gives the upper hand to queen bees as they develop.
This may reflect the costs of a high-stakes race between queen and larvae to develop quickly and gain direct fitness as heads of the colony, says Evans. Developing queens that emerge first, even if only by a matter of hours, almost always beat rival queens in gaining control of colony reproduction.