Scientists have identified how a single gene in honey bees separates the queens from the workers.
Scientists from Michigan State University and Wayne State University studied a gene in bees called Ultrabithorax or Ubx.
The gene is responsible for leg and wing development and plays a crucial role in the evolution of bees' ability to carry pollen.
"This gene is critical in making the hind legs of workers distinct so they have the physical features necessary to carry pollen," said Zachary Huang, MSU entomologist.
"Other studies have shed some light on this gene's role in this realm, but our team examined in great detail how the modifications take place," Huang said.
Specifically, the gene allows workers to develop a smooth spot on their hind legs that hosts their pollen baskets, researchers said.
On another part of their legs, the gene promotes the formation of 11 neatly spaced bristles, a section known as the "pollen comb".
The gene also promotes the development of a pollen press, a protrusion also found on hind legs, that helps pack and transport pollen back to the hive.
While workers have these distinct features, queens do not. The research team was able to confirm this by isolating and silencing Ubx, the target gene.
This made the pollen baskets, specialised leg features used to collect and transport pollen, completely disappear. It also inhibited the growth of pollen combs and reduced the size of pollen presses.
In bumble bees, which are in the same family as honey bees, queens have pollen baskets similar to workers.
In this species, Ubx played a similar role in modifying hind legs because the gene is more highly expressed in hind legs compared to front and mid legs, researchers said.
"The pollen baskets are much less elaborate or completely absent in bees that are less socially complex," Huang said.
"We conclude that the evolution of pollen baskets is a major innovation among social insects and is tied directly to more-complex social behaviours," Huang said.
The study is published in the journal Biology Letters.
