Résumé
1. Oxidative stress has been proposed as a central causal mechanism
underlying the life history trade-off between current and future
reproduction and survival in wild animals. 2. Whereas mixed evidence
suggests that maternal oxidative stress may act both as a constraint and a
cost to reproduction, some studies have reported a lack of association
between reproduction and maternal oxidative stress. 3. The oxidative
shielding hypothesis offers an alternative explanation, suggesting that
mothers may pre-emptively mitigate the oxidative costs of reproduction by
increasing antioxidant defences prior to reproduction. 4. We tested the
oxidative constraint, cost, and shielding hypotheses using a longitudinal
field study of oxidative stress levels in a species that breeds using
daily energy income, the Columbian ground squirrel (Urocitellus
columbianus). 5. Elevated maternal oxidative damage prior to reproduction
was associated with higher maternal investment in litter mass at birth,
but not at weaning. 6. Breeding females increased their antioxidant
capacity and decreased their oxidative damage from birth to lactation
compared to non-breeding females measured at the same time periods.
However, lower maternal oxidative stress during lactation was not
associated with higher offspring survival or mass growth over this period.
7. Our results provide little evidence for maternal oxidative stress
acting as a constraint on, or cost to, reproduction in Columbian ground
squirrels, but partially support the idea that oxidative shielding
occurred to buffer potential oxidative costs of reproduction.