Does more reproductive effort always increase oxidative stress in male house mice?

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Reproductive investment is expected to be costly and can reduce survival or future reproductive success. For males, competition for mates may be especially costly when attracting females requires heavy investment in sexual signals. Increased signalling effort can cause bodily damage through oxidative stress, but this had previously been demonstrated only in species with visual sexual signals.

Researchers tested whether reproductive effort—including reproduction, aggression and scent signalling—was associated with increased oxidative stress in male house mice (Mus musculus domesticus). These mice produce and deposit scent signals containing high concentrations of protein around a defended territory. The researchers manipulated male reproductive investment by housing males alone, with a female, or with a female in the vicinity of competitors.

Males breeding near competitors invested the most in scent signalling and regularly had aggressive interactions with other males. They tended to show greater oxidative damage to lipids in the gastrocnemius muscle, but showed no other indication of increased oxidative stress. In contrast, reproductive males had lower lipid oxidation in their serum and liver than males housed alone.

The results suggest that oxidative stress does not always increase simply as reproductive effort increases. The researchers proposed that the absence of a consistent increase in oxidative damage could reflect adaptive regulation of antioxidants and/or the house mouse scent signalling system, which differs considerably from the visual signalling of birds previously studied in this context.