Cooperation facilitates the colonization of harsh environments

Abstract

Animals living in harsh environments, where temperatures are hot and rainfall is unpredictable, are more likely to breed in cooperative groups. As a result, harsh environmental conditions have been accepted as a key factor explaining the evolution of cooperation. However, this is based on evidence that has not investigated the order of evolutionary events, so the inferred causality could be incorrect. We resolved this problem using phylogenetic analyses of 4,707 bird species and found that causation was in the opposite direction to that previously assumed. Rather than harsh environments favouring cooperation, cooperative breeding has facilitated the colonization of harsh environments. Cooperative breeding was, in fact, more likely to evolve from ancestors occupying relatively cool environmental niches with predictable rainfall, which had low levels of polyandry and hence high within-group relatedness. We also found that polyandry increased after cooperative breeders invaded harsh environments, suggesting that when helpers have limited options to breed independently, polyandry no longer destabilizes cooperation. This provides an explanation for the puzzling cases of polyandrous cooperative breeding birds. More generally, this illustrates how cooperation can play a key role in invading ecological niches, a pattern observed across all levels of biological organization from cells to animal societies.

Family living sets the stage for cooperative breeding and ecological resilience in birds

“…In conclusion, our analyses reveal 2 key findings that provide a novel way of understanding the evolution of cooperation in birds and suggest a resolution for earlier equivocal findings [6,7,9,10,23]. First, family living enables coping with variable environmental conditions and increases offspring survival both within and outside the breeding season [38].…”

The ecology of cooperative breeding behaviour

“…Perhaps most importantly, the dual benefits framework provides an explanation for the evolution of cooperatively breeding species where individuals benefit directly from group living in the absence of habitat saturation, something that has been the prevailing explanation for cooperative breeding behaviour for more than 50 years (Selander 1964). Finally, by distinguishing among the different ecological bases of social evolution, the dual benefits framework also opens up new directions for studying the ecological consequences of sociality, such as the expansion of niche breadth or range size (Sun et al 2014;Cornwallis et al 2017). Thus, we hope that the dual benefits framework will stimulate further discussion about the role of ecology in the evolution and maintenance of cooperative breeding behaviour, and contribute towards the development of a more general but predictive theory of social evolution.…”

“…; Cornwallis et al . ). Thus, we hope that the dual benefits framework will stimulate further discussion about the role of ecology in the evolution and maintenance of cooperative breeding behaviour, and contribute towards the development of a more general but predictive theory of social evolution.…”

The other facets of family life and their role in the evolution of animal sociality

“…in the European earwig F. auricularia; Wong & Kölliker, 2012;Kramer et al, 2017). Finally, note that further possibilities to apply advanced frameworks for cooperative breeding to the emergence of family life could, for instance, relate to the potential impact of additional environmental characteristics (such as variability and harshness; Jetz & Rubenstein, 2011;Koenig & Walters, 2015;Cornwallis et al, 2017) and life-history traits (such as longevity; Downing, Cornwallis & Griffin, 2015).…”