Policing Effectiveness Depends on Relatedness and Group Size

Abstract

Cohesion of social groups requires the suppression of individual selfishness. Indeed, worker egg laying in insect societies is usually suppressed or punished through aggression and egg removal. The effectiveness of such "policing" is expected to increase with decreasing relatedness, as inclusive fitness of group members is more strongly affected by selfish worker reproduction when group members are less closely related to each other. As inclusive fitness is also influenced by the costs and benefits of helping, the effectiveness of policing should decrease with increasing colony size, because the costs for the whole colony from selfish worker reproduction are proportionally reduced in large groups. Here, we show that policing effectiveness in colonies of the ant Temnothorax unifasciatus is low in large groups and high in small groups when relatedness is high. When we experimentally decreased the relatedness in groups, the policing effectiveness reached the same high level as in small, highly related groups, irrespective of group size. Therefore, our results indicate that policing effectiveness is simultaneously shaped by relatedness and group size, that is, an ecological factor. This may have major implications for testing policing across species of animals.

Ants Response to Human-Induced Disturbance in a Rain Tropical Forest

“…That most likely makes colonies from disturbed habitats even more prone to local extinction as low brood production decreases their ability to stabilize or increase the number of colonies in next generations. Our results concur with previous observations in other social insects that small colonies produce less (Luque et al 2013 ) or even any sexual brood (Walter et al 2011 ). Our field observations are also consistent with results of a laboratory experiment (Hartmann et al 2003 ) where P. punctata colonies with experimentally added larger number of larvae, but otherwise with size similar to that found in our disturbed habitats, were not able to rear surplus brood.…”

“…In addition, we expected for social insects that the disturbance will result in a smaller colony size. In social insects, brood productivity is strictly linked with colony size: larger colonies produce larger brood number and larger proportion of sexual brood that later may establish new colonies (e.g., Walter et al 2011 , Luque et al 2013 , DiRienzo & Dornhaus 2017 ). Therefore, the predicted smaller colony size may lead to lower brood production resulting in lower viability of populations in more-disturbed locations.…”

Terminal Investment: Individual Reproduction of Ant Queens Increases with Age

“…Beyond that, colony size was kept constant in the present study, and as increasing worker number presumably positively affects total productivity [22], [23] the effect of queen life span on reproductive success might be even more pronounced under natural conditions. Our result therefore parallels findings in bumble-bees, where a queen’s lifetime reproductive success also increases with its longevity [24].…”

Taxonomic Synopsis of the Ponto-Mediterranean Ants of Temnothorax nylanderi Species-Group

“…Members of the genus occur in a great variety of habitats and display a considerable range of social behavior [ 1 ] and associations with other organisms [ 2 ]. Because of their small colony size and easy maintenance in the lab Temnothorax species establish model systems in insect behavioral ecology and sociobiology, including studies on self-organized decision making [ 3 ], [ 4 ], [ 5 ], [ 6 ], nest construction [ 7 ], [ 8 ], nest moving [ 9 ], [ 10 ], division of labor [ 11 ], the regulation of reproduction [ 12 ], [ 13 ], [ 14 ], [ 15 ], [ 16 ] [ 17 ], [ 18 ], and host-parasite coevolution [ 19 ], [ 20 ], [ 21 ].…”