Communal breeding and cooperation in Seychelles warblers is associated with nest predation risk, not survival benefits and food availability

Description

In communally-breeding animals, conflict over access to reproduction arises because the limited resources needed for survival and reproduction must be shared between dominant and subordinate group members. Reproductive concession models have been constructed to investigate how such conflict is resolved, and how communal breeding can be evolutionarily stable. These models predict that dominants should concede a share of reproduction to subordinates when this (1) increases the dominants’ fitness and (2) prevents valuable subordinates from leaving the group. Demonstrable evidence of animals engaging in such reproductive concessions would have important implications for our understanding of the evolution of sociality across the animal kingdom, but has thus far been missing.Here, we show that dominant Seychelles warblers Acrocephalus sechellensis share reproduction in return for cooperative joint-protection of the nest and that such concessions promote group living and cooperation. Subordinates who help with incubation reduce the risk of egg predation and thus substantially increase group reproductive success in areas with high numbers of egg predators.Subordinates are more likely to gain access to reproduction within the group when predation risk is high.Since subordinates are more likely to stay and help in groups where they have the opportunity to reproduce, group living and cooperation are also more common in territories with high predation risk,regardless of food availability in the territory. Our results show that reproductive concessions can form part of a social contract between group members that underpins cooperative and communal breeding in social animals. Thus, while sociality is often considered to be selected for through habitat saturation or survival benefits derived from processes like safety-in-numbers and enhanced food processing, in Seychelles warblers sociality derives, at least partly, through reproductive benefits associated with reduced nest predation.

Period	12-Feb-2020
Event title	Netherlands Annual Ecology Meeting 2020
Event type	Conference
Conference number	13
Organiser	Netherlands Ecological Research Network (NERN)
Location	Lunteren, NetherlandsShow on map
Degree of Recognition	International