Meeting Abstract
All sexually reproducing organisms are faced with a fundamental decision: to invest valuable resources and energy in reproduction or in their own survival. This trade-off represents the ‘cost of reproduction’ and is thought to underlie a number of behavioral adaptations, including the evolution of mating systems. However, the hypothesis that costly parental care favors the evolution of cooperative breeding has not been formally tested because until recently we lacked an understanding of the mechanism that shaped the costs of reproduction. Oxidative stress—the imbalance between harmful reactive oxygen species and neutralizing antioxidants—has been demonstrated to link current reproductive effort to future survival across taxa. We test whether breeding cooperatively reduces the oxidative costs of reproduction in two sympatric species of African starlings that differ in their mating system. We show that individuals of the non-cooperative species incurred an oxidative cost of reproduction, whereas this costs was reduced in individuals of the cooperatively breeding species. These oxidative costs were not related to individuals’ investment in nest guarding or offspring provisioning, but increased with a general index of breeding workload (number of chicks * age of chicks). Furthermore, oxidative costs were lowered in individuals of the cooperatively breeding species because the breeding workload was shared among numerous individuals, yielding a lower per capita workload than in non-cooperative individuals. This research represents a unique comparison across two sympatric species of birds demonstrating that cooperative breeding does reduce the oxidative costs of reproduction. As such, our work supports the theory that the costs of reproduction play a role in shaping the evolution or maintenance of mating systems.
