The bee that would be queen

A team of researchers from Arizona State University, Purdue University and the Norwegian University of Life Sciences has discovered evidence that honeybees have adopted a phylogenetically old molecular cascade – TOR (target of rapamycin), linked to nutrient and energy sensing – and put it to use in caste development.

The findings, published in the June 6 edition of PLoS ONE, the online, open-access journal from the Public Library of Science, show that TOR is directly linked in the nutrient-induced development of female honeybees into either queens, the caste of large dominant egg-layers, or into workers, the caste of small helpers.

“Our study provides three independent lines of evidence – gene expression, pharmacology and RNA interference (RNAi) – that converge on one conclusion: selection can have acted on the TOR pathway to enable two distinct phenotypes to evolve in the bee,” says Gro Amdam, an assistant professor in ASU’s School of Life Sciences.

The researchers found that queen-fate can be blocked, and that workers develop, when TOR activity is reduced during development.

Amdam notes that while social insect queens and workers have been subjects of great fascination for centuries, and scientific study for the last few decades, the gene regulatory pathways responsible for determining caste fate has remained largely unknown. This is the first time a genetic pathway has been identified to control these two phenotypes, says Amdam, who heads social insect studies in laboratories at both ASU and the Norwegian University Department of Animal and Aquacultural Sciences.

“The finding that queens and workers can emerge from an old pathway that controls tissue growth in a variety of species, including humans, helps us understand what evolution builds on when it produces seemingly radically new phenotypes,” Amdam says.