Cooperation in non-family groups as a strategy for reproducing in variable climates

Christina Hansen Wheat, Emily O'Connor, Philip Ashleigh Downing, Ashleigh S Griffin, Charlie Kinahan Cornwallis 

The global climate is changing to be more extreme and less predictable, threatening many species. Cooperative breeding is more common under such conditions, indicating it may improve resilience to challenging climates. However, whether specific features of cooperative breeding systems, such as how groups form and how large they become, evolved to cope with particular climates is unclear. We test two predictions using phylogenetic analyses across birds. First, cooperative groups formed by unrelated adults (‘nonfamily’) are an adaptation to variable environments. Nonfamily groups can form relatively quickly when conditions deteriorate, unlike family groups, which often require offspring retention over multiple generations. Second, species with larger groups are able to breed in more extreme environments. We found that as climates get hotter and precipitation becomes more variable, cooperative breeding with nonfamily is more frequent and groups become larger (nspecies=39). Conversely, cooperative breeding in family groups is more frequent in stable, hot environments (nspecies=128). Additionally, both nonfamily and family cooperative species had broader climatic niches than phylogenetically matched pair breeders (nspecies=456). Our results highlight that cooperation with unrelated individuals may enable species to live in hot environments with variable rainfall that are expected to become more common in the future.