Physiological and behavioural costs of traits linked to reproductive success in wild-derived house mice.

Abstract

The early-life environment can have profound effects on offspring development and behaviour into adulthood. There are physiological and behavioural trade-offs associated with altered developmental strategies as a result of responding to environmental cues. Oxidative stress, a physiological mechanism that can lead to decreased reproductive output and increased aging, has also been suggested to be a main consequence mediating investment in life-history traits, particularly reproductive effort. I aimed to examine the effects of developmental environments on reproductive effort and oxidative stress in young wild-derived mice, Mus musculus domesticus. I also examined age-related differences in sexual signalling and aggression in young adult and old male mice. I altered the early-life environment by manipulating litter size or introducing social cues in wild-derived mice and measured developmental and reproductive traits as well as markers of oxidative stress. Pups from enlarged litters suffered higher oxidative challenges compared to those from reduced litters. Male young exposed to male scents also exhibited lower levels of markers indicating oxidative stress, although this result was not consistent through all assays examined. However, males from enlarged litters and those exposed to female cues increased investment in sexual signalling, irrespective of potential increased oxidative challenges. Mothers exposed to male cues during pup rearing decreased maternal care at peak pup development age. Interestingly, male young exposed to male cues at weaning age suppressed their growth rate, whereas those that were raised with male cues from birth grew at a faster trajectory, possibly as a result of altered maternal care. When examining differences in reproductive effort between older and younger adult males, older males scent marked more frequently and were significantly more aggressive, although they had lower major urinary protein levels than younger adult males. Interestingly, both young and old males scent marked more frequently after competitive encounters regardless of the outcome. While I did find evidence of oxidative stress potentially mediating reproductive effort, especially in offspring from experimentally enlarged litters, it did not explain all the differences in reproductive effort measured. I also found that the early-life environment had significant impacts on growth and traits linked to reproductive investment post-weaning, especially in male mice.