Worker-like behavioral and physiological phenotype in queens with removed wings in a ponerine ant

Abstract

Many highly eusocial insects are characterized by morphological differences between females which are especially pronounced in ants. How these differences associate with particular behavioral and physiological phenotypes can illuminate early ant evolution. In ants, the morphological queen usually possesses a larger thorax with wings compared to a wingless worker. While queens specialize in reproduction, workers help with nonreproductive tasks and show various levels of reproductive degeneration. Here, we investigated the level of behavioral and physiological plasticity within queens in the ant species Harpegnathos saltator which shows limited queen-worker dimorphism. We found that the experimental removal of wings led to the expression of worker behaviors and physiology by examining young queens with wings, known as alate gynes, and those whose wings have been experimentally removed or naturally shed, known as dealate gynes. Compared to alate gynes, dealate gynes displayed higher frequencies of behaviors that are naturally shown by workers during reproductive competition. In addition, dealate gynes exhibited a worker-like range of ovarian activity. Like workers, they lacked the putative sex pheromones on their cuticle characteristic of dispersing gynes. Because gynes activate a worker-like phenotype after wing removal, the essential difference between the queen and worker in this species is a dispersal polyphenism. If the queen plasticity observed in H. saltator reflects the early stages of ant eusociality, a dispersal dimorphism rather than a distinct reproductive dimorphism might represent an early step in ant evolution.