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

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

Climate change is making conditions more extreme and variable, threatening many species. Cooperative breeding can be more common under such conditions, suggesting it may improve resilience to climate change. However, it is unclear whether specific features of cooperative breeding systems, such as how groups form and how large they become, evolved in response to particular climate challenges. We test two predictions using phylogenetic analyses across birds. First, cooperative breeding with unrelated individuals (‘nonfamily’) is an adaptation to variable environments. Nonfamily groups can form relatively quickly when conditions deteriorate, in contrast to family groups, which typically form when individuals remain in their natal areas over multiple generations. Second, species with larger groups are able to breed in more extreme environments. Nonfamily cooperative breeding was more frequent and group sizes were larger (nspecies=39) in hotter climates with more variable precipitation. Conversely, cooperative breeding in family groups was more frequent in stable, hot environments and group sizes were not related to climate (nspecies=128). Both nonfamily and family cooperatively breeding species also had broader climatic niches than phylogenetically matched pair breeders (nspecies=456). These results highlight that cooperation with unrelated individuals may enable species to live in hot environments with variable rainfall, which are expected to become more common in the future.