Social mutilation in the Ponerine ant Diacamma: cues originate in the victims

Abstract

In the queenless ponerine ant genus Diacamma, all workers eclose with a pair of innervated thoracic appendages termed gemmae. The gamergate (= mated egg laying worker) maintains reproductive monopoly by mutilating the gemmae of all eclosing individuals. Such mutilation leads to irreversible behavioural and neurological changes such that the individual lacking gemmae becomes incapable of appropriate sexual calling and mating. In one population related to Diacamma ceylonense from India, Diacamma sp. from Nilgiri (hereafter referred to as 'nilgiri'), gamergates do not mutilate their nestmates and yet maintain reproductive monopoly. To understand what triggers mutilation, we exchanged cocoons between the mutilating D. ceylonense colonies and the non mutilating 'nilgiri' colonies. 'nilgiri' callows were not mutilated even in D. ceylonense colonies while D. ceylonense callows were mutilated even in 'nilgiri' colonies, suggesting that the cues for mutilation originate in the victims (callows), presumably in the gemmae themselves. This finding should facilitate understanding the proximate mechanism and evolutionary significance of mutilation of gemmae as a method of resolution of reproductive conflicts in the genus Diacamma.