Dietary carotenoid availability and reproductive effort influence the age-related decline in performance

Elevated breeding effort is known to increase an individual's rate of senescence, although the underlying mechanisms are not well understood. One possibility is that the ability to resist senescence is limited by the availability of antioxidants, which are necessary to mitigate the deleterious effects of oxidative stress thought to underlie the aging process. Susceptibility to oxidative stress is likely to be particularly high during reproduction, and so for a given level of reproductive effort, the rate of senescence should be fastest in those individuals with the poorest antioxidant capacity. We tested this hypothesis in an experimental study of breeding male three-spined sticklebacks (Gasterosteus aculeatus) held under a high or low reproduction regime and fed on either high or low levels of carotenoids (potentially limiting dietary compounds with antioxidant properties). Fish on the high reproduction regime and those on the low-carotenoid diet both showed an accelerated decline in sustained swimming performance (an indicator of locomotor senescence) compared with males on the low reproduction regime and high-carotenoid diet, respectively. The swimming performance of fish subjected to the high rate of reproduction, but fed a low-carotenoid diet, appeared to decline most rapidly, perhaps because of the additive effects of increased levels of reproduction-induced oxidative stress and lower antioxidant availability. These findings show that both dietary carotenoid intake and breeding effort can impact on the age-related decline in swimming performance and have important implications for female choice and the capacity of males with insufficient antioxidant defenses to adequately perform paternal care.