In animal societies, cooperation can confer long-term benefits, including a boost to future breeding and survival. How can sharing a workload now allow an animal to breed more in the future? Equally, how can working hard now have a detrimental effect on future reproduction and longevity? I had a feeling oxidative stress may play a role.
I wanted to test whether reproductive effort increased exposure to oxidative damage, and whether cooperative sharing of workloads could reduce these costs. To address this, I used a tricky clutch-removal experiment, lots of videos of feeding at the nest, and much blood sampling.
The results revealed that, in small breeding groups, the costs of reproduction were clear: elevated exposure to harmful oxidative damage, which can lead to future diseases and ageing. However, in big breeding groups, there were no such costs. In larger social groups, additional helpers were sharing the burden of offspring care, and allowing all birds to avoid exposure to oxidative stress. Work rate even scaled with antioxidant protection: those that worked hardest had the weakest antioxidant defences.
This was by far my favourite paper to emerge from my PhD research on the sparrow weaver project. The results suggest that oxidative stress may play a central role in the evolution of cooperation: while reproduction can carry significant costs, cooperative 'oxidative load-lightening' may have evolved to avoid these costs!