Abstract
1. Investment in reproduction is anticipated to be costly and can decrease survival or future reproductive success. For males, substantial reproductive costs may be accrued when competing for mates, particularly when individuals need to invest heavily in the production of sexual signals to attract females. On a proximate level, increased male signalling effort can cause somatic damage because of oxidative stress, although this has been demonstrated only in species with visual sexual signals.
2. We tested whether reproductive effort (comprising reproduction, aggression and scent signalling) is associated with increased oxidative stress in male house mice (Mus musculus domesticus). Sexual signalling in this species involves the production and deposition of scent signals containing a high concentration of protein around a defended territory. Male reproductive investment was manipulated by housing males alone, with a female or with a female and in the vicinity of competitors.
3. Males breeding in the vicinity of competitors invested the most in olfactory signalling as well as having regular aggressive interactions with other males. These males tended to show greater oxidative damage to lipids in the gastrocnemius muscle but no other indication of increased oxidative stress. Instead, lipid oxidation was lower in the serum and liver of reproductive males compared with those housed alone.
4. Our results highlight that oxidative stress does not always occur simply as a function of increasing reproductive effort. The lack of a consistent increase in oxidative damage could be due to adaptive regulation of antioxidants and / or a consequence of the scent signalling system of house mice, which differs considerably from the visual signalling of birds previously examined in this context.