title: Group-size-dependent punishment of idle subordinates in a cooperative breeder where helpers pay to stay.
abstract: In cooperative breeding systems, dominant breeders sometimes tolerate unrelated individuals even if they inflict costs on the dominants. According to the 'pay-to-stay' hypothesis, (i) subordinates can outweigh these costs by providing help and (ii) dominants should be able to enforce help by punishing subordinates that provide insufficient help. This requires that dominants can monitor helping and can recognize group members individually. In a field experiment, we tested whether cooperatively breeding cichlid Neolamprologus pulcher subordinates increase their help after a forced 'idle' period, how other group members respond to a previously idle helper, and how helper behaviour and group responses depend on group size. Previously, idle helpers increased their submissiveness and received more aggression than control helpers, suggesting that punishment occurred to enforce help. Subordinates in small groups increased their help more than those in large groups, despite receiving less aggression. When subordinates were temporarily removed, dominants in small groups were more likely to evict returning subordinates. Our results suggest that only in small groups do helpers face a latent threat of punishment by breeders as predicted by the pay-to-stay hypothesis. In large groups, cognitive constraints may prevent breeders from tracking the behaviour of a large number of helpers.
authors.affiliation: Behavioural Ecology, Institute of Ecology and Evolution, University of Bern, Wohlenstrasse 50a, 3032 Hinterkappelen, Switzerland stefan.fischer@iee.unibe.ch.
authors.forename: Stefan
authors.initials: S
authors.lastname: Fischer
authors.affiliation: Behavioural Ecology, Institute of Ecology and Evolution, University of Bern, Wohlenstrasse 50a, 3032 Hinterkappelen, Switzerland Department of Zoology, University of Cambridge, Cambridge, UK.
authors.forename: Markus
authors.initials: M
authors.lastname: Zöttl
authors.affiliation: Behavioural Ecology, Institute of Ecology and Evolution, University of Bern, Wohlenstrasse 50a, 3032 Hinterkappelen, Switzerland Behavioural Ecology and Self-Organization, Centre for Ecological and Evolutionary Studies, University of Groningen, Groningen, The Netherlands.
authors.forename: Frank
authors.initials: F
authors.lastname: Groenewoud
authors.affiliation: Behavioural Ecology, Institute of Ecology and Evolution, University of Bern, Wohlenstrasse 50a, 3032 Hinterkappelen, Switzerland.
authors.forename: Barbara
authors.initials: B
authors.lastname: Taborsky
mesh_terms: D000374:Aggression; D000818:Animals; D023681:Cichlids / Q000502:physiology*; D005260:Female; D006379:Helping Behavior; D008297:Male; D011156:Population Density; D011678:Punishment; D012098:Reproduction / Q000502:physiology*; D012919:Social Behavior; D012930:Social Dominance
keywords: cichlids; conflict; cooperation; eviction; helping; territory defence