ORIGINAL PAPER Worker self-restraint and policing maintain the queen’ s reproductive monopoly in a pseudomyrmecine ant Volker S. Schmid & Martin Kaltenpoth & Erhard Strohm & Jürgen Heinze Received: 14 August 2012 / Revised: 28 December 2012 / Accepted: 4 January 2013 / Published online: 24 January 2013 # Springer-Verlag Berlin Heidelberg 2013 Abstract Division of reproductive labor in insect societies is often based on worker self-restraint and both queen and worker policing. Workers of many hitherto studied wasps, bees and ants do not lay eggs in the presence of a queen. However, it is presently unclear how far these observations in a few select clades can be generalized. We investigated if and how queens maintain a reproductive monopoly in col- onies of the elongate twig ant, Pseudomyrmex gracilis,a member of the previously unstudied ant subfamily Pseudomyrmecinae. Colonies are usually headed by a sin- gle, singly mated queen (monogyny, monandry). Workers therefore would be more closely related to males produced by other workers (r =0.375) than to the sons of queens (r = 0.25). Nevertheless, workers appear to refrain from laying male-destined eggs in the presence of the queen. In queen- less conditions, workers form dominance hierarchies by antennal boxing, and only one or a few high-ranking indi- viduals readily begin to lay eggs. When returned into a queenright colony, egg-laying workers are immediately bit- ten, stung and expelled or killed by other workers. While the composition of cuticular hydrocarbons clearly differed be- tween castes, it less clearly reflected worker ovarian devel- opment. An association with worker ovarian development that would allow workers to monitor the reproductive status of nestmates could only be tentatively postulated for certain substances. Our study broadens our knowledge about repro- ductive conflict in social Hymenoptera and shows that worker sterility in the presence of a queen is more common in monogynous, monandrous ants than expected from relat- edness alone. Keywords Cuticular hydrocarbons . Dominance . Policing . Pseudomyrmex gracilis . Reproductive conflict . Worker reproduction Introduction The cohesiveness and smooth functioning of insect societies require that internal disagreements among nestmates are resolved (Ratnieks et al. 2006). Though the societies of ants, bees and wasps often appear to be harmonious “superorgan- isms” (e.g., Hölldobler and Wilson 2008), kin selection theory predicts the occurrence of several conflicts of inter- est. For example, workers and queens may have different preferences concerning the origin of males (e.g., Ratnieks 1988; Monnin and Ratnieks 2001; Heinze 2004; Ratnieks and Wenseleers 2005; Ratnieks et al. 2006; Ohtsuki and Tsuji 2009). Workers are most closely related to their own sons (life-for-life relatedness r =0.5). In colonies with a single, singly mated queen (monogyny and monandry), workers are also more closely related to the males produced by sister workers (r =0.375) than to the males produced by the queen (r =0.25). Based on relatedness alone, workers should therefore prefer worker-produced sons over queen- produced sons. Workers of most species of social Hymenoptera are ca- pable of producing haploid males from unfertilized eggs after the death of their queen (e.g., Crozier and Pamilo 1996). Which worker lays eggs and which does not may be regulated by antennal boxing, biting, jerking and other types of dominance interactions among the workers, in Communicated by L. Sundström Electronic supplementary material The online version of this article (doi:10.1007/s00265-013-1476-y) contains supplementary material, which is available to authorized users. V. S. Schmid (*) : M. Kaltenpoth : E. Strohm : J. Heinze Biologie I, Universität Regensburg, 93040 Regensburg, Germany e-mail: volker.schmid@biologie.uni-regensburg.de M. Kaltenpoth Research Group Insect Symbiosis, Max Planck Institute for Chemical Ecology, Hans-Knöll-Str. 8, 07745 Jena, Germany Behav Ecol Sociobiol (2013) 67:571–581 DOI 10.1007/s00265-013-1476-y