Abstract

Although division of labor as a means to increase productivity is a common feature in animal social groups, most previous work has focused almost exclusively on eusocial insects with extreme task partitioning. Empirical evidence of division of labor in vertebrates is scarce, largely because we lack a theoretical framework to explore the conditions under which division of labor is likely to evolve. Here we model how individual decisions on task specialization may select for the emergence of division of labor under both direct and indirect fitness benefits by explicitly considering alternative helping tasks with varying fitness costs (i.e., some tasks are likely to lead to injury or death, while others impact an individual's body mass and reproductive success more strongly due to lower feeding rates and energy investment). We find that: (1) direct survival fitness benefits of living in larger groups are the primary driving force of cooperation to enhance group productivity; (2) indirect fitness benefits derived from related group members are a non-essential facilitator for more stable forms of division of labor; and (3) division of labor is favored by increasingly harsh environments. Ultimately, our model not only makes key predictions that are consistent with existing empirical data, but also proposes novel avenues for new empirical work in vertebrate and invertebrate systems alike.