Nestmate interactions and egg-laying behaviour in the queenless ponerine ant Rhytidoponera sp. 12

Abstract

Rhytidoponera sp. 12 is a polygynous Australian arid-zone queenless ponerine ant with morphologically identical mated workers (gamergates) and unmated workers. Discriminating gamergates from virgin workers in R. sp. 12 is therefore difficult. All females have functional ovaries and spermatheca. The ability of unmated workers to lay trophic eggs has not been reported. In four R. sp. 12 colonies we found that gamergates have tough reddish-brown cuticle differing from that of the dark brown unmated workers. Gamergates were successfully identified by combining this observable morphological difference with previously described behavioural traits thus eliminating the need of identification through dissection. In a laboratory-kept colony gamergates showed mutual tolerance. Egg-shuffling behaviour by gamergates was observed. A high proportion of unmated workers laid trophic eggs that were either cannibalised or shared between nestmates; larvae were observed to feed exclusively on these trophic eggs. Eggs laid by gamergates were sometimes eaten, although the majority of these were deposited onto egg piles carried by unmated workers. Oophagy of viable eggs by gamergates may represent a form of dominance behaviour or, together with egg-shuffling, a behaviour to resist manipulation by less fecund gamergates. Removing gamergates from three colonies led to oocyte development in some unmated workers, indicating that ovarian development in virgin workers may be reduced in the presence of gamergates.