Oxidative stress is pervasive in all forms of life, represents a major selective pressure imposed on all organisms and potentially mediates life-history trade-offs. Vertebrate spermatozoa are very susceptible to oxidative stress, which affects sperm performance and reduces male fertility and Darwinian fitness. This should especially be true in species where males face sperm competition, the circumstance where sperm of two or more males compete to fertilise the same egg. Interestingly, sperm competition theory predicts that low-ranking males should invest more into their germline at the expense of their soma whereas dominant, high-ranking males should invest more into the somatic traits conferring greater access to females (the soma/germline allocation trade-off). Because both somatic functions and sperm cells likely suffer from oxidative stress, males may face a trade-off in the allocation of antioxidant resources to either the protection of their soma or the protection of their germline. The soma/germline allocation trade-off hypothesis therefore predicts that high-ranking males should preferentially invest their antioxidant defences in somatic functions whereas low-ranking males should preferentially invest their antioxidant defences in their germline. This project aims at testing whether antioxidant allocation strategies into soma or germline underlie the development of reproductive tactics according to social status as predicted by sperm competition models. This goal will be achieved using a combination of field observations, field experiments and aviary experiments.
Sperm quality, antioxidant allocation to soma vs. germline and social status in a natural population. I plan to establish long-term monitoring of a natural population of house sparrows breeding in nest boxes. Regular observations and captures will provide data on social status, redox balance in soma and germline and sperm quality. We will thus be able to investigate the natural co-variation between sperm quality, antioxidant allocation to soma vs. germline and social status.
Experimental manipulation of oxidative stress and dietary antioxidant availability. We will use captive house sparrows to test whether and how a) exposure to a pro-oxidant toxicant, b) supplementation with dietary antioxidant and c) parasite infestation affect a male’s oxidative status and sperm quality and differentially affect antioxidant allocation to soma vs. germline according to male social status.
Experimental manipulation of social status. We will use captive house sparrows to test experimentally whether and how a change in a male’s social status affects his antioxidant allocation strategy to soma vs. germline and sperm quality.
Oxidative stress and dietary antioxidant availability during early development. We will use experiments and long-term monitoring of a natural population of house sparrows breeding in nest boxes to test the hypothesis that oxidative challenges and dietary antioxidant availability during early development affect social status, and thus determine antioxidant allocation strategies to soma vs. germline and sperm quality in adulthood.