An obscure group of animals may reveal the secret of elongating life

THE one sure way to prolong an animal's life is, paradoxically, to starve it. "Caloric restriction", as it is known in the trade, works for everything from threadworms to mammals (people included, as far as can be ascertained without the luxury of controlled experiments). So it is no surprise that it also works for a group of small creatures known as rotifers. If that were the only result of Shugo Watabe's experiments on the critters, at the University of Tokyo, it would scarcely be worth reporting. What makes this news is that the offspring of the rotifers in question also lived longer than normal. And that—the inheritance of an acquired characteristic—is quite startling.

Rotifers are unusual in that they often reproduce by parthenogenesis (some species, indeed, can reproduce only in this way). A parthenogenetic population is, by definition, all female and the result, give or take the odd mutation, is that a rotifer's daughters are genetically identical to her. That makes rotifers convenient subjects for studies of the controversial idea that characteristics acquired during an individual's life can be passed down the generations in ways that are independent of mutations in the DNA.

Dr Watabe and his colleagues first looked at whether caloric restriction does, indeed, work its magic on rotifers. It does. Without it, as they report in Functional Ecology, their animals lived for an average of 8.8 days. With it they lived for 13.5 days. The intriguing result came when they did the same thing with the rotifers' offspring. The daughters of those rotifers which had been fed as much as they could eat lived for 9.5 days if treated likewise (not significantly different from their mothers) and 14.4 if put on short commons. Those born of calorie-restricted mothers lived for 12.7 and 16.8 days respectively. Something, then, is being passed on that is having an effect down the generations.

That something seems to be related to an enzyme called catalase. This enzyme degrades hydrogen peroxide, a highly reactive chemical that creates cellular damage of the sort associated with ageing. Dr Watabe found that the offspring of calorie-restricted mothers have more catalase than those of mothers who were fed without restriction.

The researchers also detected higher levels of the enzyme in the eggs of calorie-restricted mothers, so it could be that their offspring are simply endowed with the stuff. A more intriguing possibility, though, is that the relevant genes are affected by epigenesis, a process in which chemicals attached to the DNA control its activity. Epigenetic modifications are often retained when cells divide, and can sometimes be passed on to offspring.

If inherited epigenetic changes were causing daughter rotifers to produce more catalase, it would raise the question of whether a similar thing happens in other species and, if so, whether it might be induced artificially, without all the tedious business of a lifetime's starvation. That would certainly be worth looking at. The search for an elixir of life has taken people to some strange places. Few, though, are stranger than rotifers.