Worker policing without genetic conflicts in a clonal ant

Abstract

In group-living animals, mutual policing to suppress reproduction is an important mechanism in the resolution of conflict between selfish group members and the group as a whole. In societies of bees, ants, and wasps, policing against the production of males by other workers is expected when egg laying by workers decreases the average inclusive fitness of individual group members. This may result (i) from the relatedness of workers being lower to worker-than to queen-derived males or (ii) from a lowered overall colony efficiency. Whereas good evidence exists for policing behavior caused by genetic conflicts, policing caused by efficiency factors has not been demonstrated. We investigated the regulation of reproduction in the ant Platythyrea punctata, a species in which colonies are clones because workers are capable of producing female offspring by thelytokous parthenogenesis. Reproductive conflicts resulting from differences in genetic relatedness are therefore not expected, but uncontrolled reproduction by all workers could lead to the destruction of sociality. Here we show that worker policing by aggressive attacks against additionally reproducing workers keeps the number of reproducing workers low. Furthermore, through experimental manipulation of the number of brood items per colony, we show that worker policing can enhance group efficiency.

Comparative Analysis of Worker Reproduction and Policing in Eusocial Hymenoptera Supports Relatedness Theory

“…(Kikuta and Tsuji 1999). Worker policing has even been found in species that reproduce parthenogenetically: the ant Platythyrea punctata (Hartmann et al 2003) and the Cape honeybee Apis mellifera capensis ; but also see Moritz et al 1999;Beekman et al 2002) and also in two species where workers are equally related to the queen's sons as to other workers' sons (Vespula vulgaris and Formica fusca). In these cases, worker policing is selectively neutral on relatedness grounds.…”

“…As a result, worker policing can have colony-level benefits, particularly if policing occurs through aggression and causes reproductive workers to work rather than reproduce (e.g., in A. smythiesi [Iwanishi et al 2003] and P. punctata [Hartmann et al 2003]). Theory has shown that if worker policing has colony-level benefits, it can be selected for even under single mating (Ratnieks 1988).…”

“…However, in many species, workers kill or "police" other workers' eggs before they can hatch (reviewed in Wenseleers et al 2004b;Ratnieks and Wenseleers 2005;Ratnieks et al 2006). In some species, workers even aggress nestmates with active ovaries, which can result in the victim being killed or cause it to regress its ovaries (Visscher and Dukas 1995;Monnin and Ratnieks 2001;Hartmann et al 2003;Iwanishi et al 2003;Ratnieks et al 2006). The result of this policing behavior is that the reproductive division of labor is reinforced, with more of the colony's males being the queen's sons.…”

“…More recent data, however, show that worker policing also occurs in species where queen mating frequency is below 2, for example, in the ant Camponotus floridanus (Endler et al 2004) and the hornet Vespa crabro (Foster et al 2002), or in species that reproduce parthenogenetically, such as the ant Platythyrea punctata (Hartmann et al 2003) and the Cape honeybee Apis mellifera capensis see table A1). This has led to doubts concerning the importance of relatedness in selecting for worker policing (Foster et al 2002;Hartmann et al 2003;Pirk et al 2003Pirk et al , 2004Endler et al 2004;Gadagkar 2004;Wilson 2005).…”

“…This has led to doubts concerning the importance of relatedness in selecting for worker policing (Foster et al 2002;Hartmann et al 2003;Pirk et al 2003Pirk et al , 2004Endler et al 2004;Gadagkar 2004;Wilson 2005). This doubt was reinforced by , who used a comparative analysis of 50 species of ants, bees, and wasps to show that the proportion of males that are workers' sons is not influenced by relatedness.…”