Caste differentiation in ants

A specific hormone appears to have a decisive effect on whether ants become queens or worker ants. Their fate is determined as early as the embryonic stage.

A new research study from Department of Biology, University of Copenhagen finds that excess juvenile hormone can redirect the development of worker ants, giving them reproductive queen-like traits.

As early as embryo development, many colony-dwelling insects become specialized for either reproduction or labor as queens or workers, respectively. In some ant species, juvenile hormone (JH) induces queen-worker differentiation as early as embryo development, but whether this hormone can impact the developmental trajectory of ants after the onset of differentiation is still unclear.

Ruyan Li, PhD-student at Department of Biology and his research colleagues fed 237 Pharaoh ant worker larvae with controlled doses of juvenile hormone during the first half of the 3^rd larval instar, the final stage of larval development.

The group documented the ants’ physical characteristics, behavior, and gene expression for 30 days as they grew into adults. They found that hormone-treated worker ants took on queen-like physical characteristics, such as increased body length, compound eyes, flight muscles, brain size, and spermatheca, the female organ used to store spermatozoa.

They then isolated a set of 95 (JH)-hormones-sensitive genes likely responsible for the development of queen-like traits in workers. The workers also took on queen-like behavioral patterns, characterized by reduced locomotion and foraging behavior.
However, unlike queens, JH-treated workers did not develop ovaries. The results suggest that Pharaoh ants have non-overlapping developmental windows during which JH can influence reproductive organ development and the development of bodily characteristics.