The evolution of paternal care: a role for microbes?

Paternal care is an evolutionary mystery. Despite extensive research, both theoretical and experimental, the reasons for its ubiquity remain unclear. Common explanations include kin selection, suggesting that the benefits to the offspring outweigh the costs to the father’s future reproductive success, and limited accuracy in parentage assessment. However, these explanations do not cover the breadth of circumstances in which paternal care has been observed, particularly in conditions of uncertainty in paternity. Many recent studies presented associations between microbes and complex behavioural traits, including anxiety, depression, and autism spectrum disorders. Here we propose that microbes may play a key role in the evolution of paternal care. Using computational models, we demonstrate that microbes associated with increased paternal care could be favoured by natural selection. We find that microbe-induced paternal care could evolve under wider conditions than suggested by genetic models. Moreover, we show that microbe-induced paternal care is more likely to evolve when considering paternal care interactions that increase microbial transmission, such as feeding and grooming. Our results suggest that factors affecting the host microbiome, such as antibiotics or specific foods, could also affect paternal behaviour.