28 July 2010, by Adele Rackley

No parent will be surprised to hear that diverting energy into having kids accelerates the ageing process – but the good news is that antioxidants help, at least if you're the father.

Two sticklebacks

Three-spined sticklebacks in breeding colouration

Scientists have shown that sticklebacks fare better at parenthood when they have a diet rich in antioxidant carotenoids.

Carotenoids are known to reduce damage caused by free radicals, which accelerate the ageing process.

The theory is that high-energy activity like reproduction causes an increase in the production of free radicals, so breeding animals will be particularly susceptible to their effects, and more so if their supply of antioxidants can't keep up. The oxidative stress caused by free radicals is thought to underlie the ageing process – or 'senescence' – so a diet rich in antioxidants should help defend against the ageing effects of reproduction.

'These effects should apply to any species where the male invests heavily in parental care.'

Dr Tom Pike, University of Exeter

Researchers from the Universities of Glasgow and Exeter tested this idea on three-spined sticklebacks (Gasterosteum aculeatus). They controlled the sticklebacks' diet and breeding rates, and measured senescence by testing their swimming endurance. The results, published in Behavioural Ecology, indicate that a diet rich in anti-oxidants does seem to make a difference.

'Reproduction is costly,' says lead author Dr Tom Pike from the University of Exeter, who was at the University of Glasgow when he did the research. 'The more you reproduce the earlier you die. We wanted to find out why.'

Sticklebacks make ideal subjects because many populations have just one breeding season which means they must produce lots of broods in a short time. It's particularly hard on the males because they're responsible for childcare too. Sticklebacks use carotenoids to produce sexual signals, so this anti-oxidant is likely to be in short supply when the fish are breeding.

The scientists captured a sample of sticklebacks from a Scottish river and fed half the fish a carotenoid-rich diet, and the other half a low-carotenoid diet.

Forty males from each dietary group were then put in separate tanks with nesting material, and were shown a sexually mature female for ten days until they'd made a nest.

Three-spined stickleback

Three-spined stickleback.

The researchers then measured each breeding male's sustained swimming performance - the amount of time it could swim against a current of water.

The fish were allowed to mate, then the group was divided again. Half the fish from each of the dietary groups (high and low carotenoids) went through the exact same process until the cycle of breeding had been completed three times. The remaining fish did not reproduce again.

The swimming endurance of both the high and low reproduction groups continued to be monitored after each 20-day cycle.

At the end of the study, the fish that had gone three rounds on a low-carotenoid diet had fared much worse than the other three groups; their endurance levels had dropped significantly.

'Our results show that both dietary carotenoid intake and breeding effort have an impact on how quickly the sticklebacks' swimming performance declines,' explains Pike.

'We thought we'd see roughly these results, but carotenoids aren't thought to be particularly effective antioxidants, so we were surprised that they seem to have such a big effect.'

These findings have important implications for breeding males, because females prefer a mate that looks fit enough to cope with the physical stresses of fatherhood.

Male sticklebacks put a lot of effort into nurturing and fanning their eggs. So fathers that lack carotenoids will be less likely to produce a healthy brood, and might not even have the energy to attract their next mate.

And, says Pike, 'These effects should apply to any species where the male invests heavily in parental care.'

The researchers emphasise that other factors – loss of energy or susceptibility to parasites for example – could also have a bearing on the results and that further work is needed to unravel all the relationships.