Loss of wings induces the expression of the worker-like phenotype in queens of a ponerine ant

Abstract

Many highly-eusocial insect species are characterized by morphological differences between females. This is especially pronounced in ants where queens usually possess a fully developed thorax with wings and are specialized for reproduction while workers have a reduced thorax without wings and show various levels of reproductive degeneration that is associated with their helper role in the colony. Despite their morphological differentiation, queens and workers still show some plasticity leading to overlapping behavioral and physiological phenotypes. We investigated the level of queen plasticity and the factor that induces a worker-like phenotype in the ant species Harpegnathos saltator that has limited queen-worker dimorphism and workers that can assume the reproductive role of a queen in the colony. By comparing alate and dealate young queens, so-called gynes, we found that the loss of wings initiated the expression of behavioral and physiological characteristics of ant workers. In contrast to alate gynes, dealate gynes displayed higher frequencies of worker-like behaviors. In addition, dealate gynes showed a worker-like range of reproductive states unlike alate gynes. Like workers, dealate gynes lost the chemical signaling that is characteristic of alate gynes. Since gynes can activate this worker-like phenotype after wing loss, the essential difference between the ant queens and workers in this species with limited queen-worker dimorphism is a dispersal polyphenism. If the phenotypic plasticity observed in H. saltator is representative of the early stages of ant eusociality, an emerging dispersal dimorphism rather than a distinct reproductive dimorphism might represent one of the first steps in ant evolution. Summary StatementAnt queens who have lost their wings express worker-like behaviors and physiology including the display of dominance behavior during hierarchy establishment, which is normally a worker-only behavior in this species.