THE war on ageing has opened up a new front in the wilds of nature. After decades of poring over fruit flies and worms in the lab, it is time to find out how different species grow old naturally and how genes related to ageing play out in real environments.
Until recently, researchers who study the genetic and molecular mechanisms of ageing thought they had little to learn from wild animals. They tended to believe that few of them ever lived long enough to show the decrepitude of old age. So they opted for lab organisms because they are easy to raise and have short lives.
Only in the past few years have field biologists accumulated the careful, long-term evidence that proves senescence really does occur in the wild.
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鈥淲hen you get to natural populations, which are more difficult to study, there you have organisms which are actually living a long time. It would be nice to know what they鈥檙e doing,鈥� says Robert Ricklefs at the University of Missouri, St Louis, one of several evolutionary biologists to describe their new approach in the June issue of Functional Ecology (vol 22, p 371).
This opens the door for gerontologists to go out and ask how organisms actually age. Already, they are finding interesting cases worth following up in more detail. For example, some bird species, such as terns and kittiwakes (see picture), remain remarkably vigorous right into old age. 鈥淭hese birds are raising chicks right up until they die, and doing a pretty good job of it,鈥� says Ricklefs. 鈥淭hat鈥檚 a pretty spectacular result. Mammals don鈥檛 seem to age that way.鈥�
鈥淪ome birds, such as terns and kittiwakes, remain remarkably vigorous right into old age. Mammals don鈥檛 age that way鈥�
Honeybees, too, show great promise in the study of ageing. The workers, in particular, vary greatly in lifespan despite their highly similar genetic background. 鈥淚t鈥檚 like you suddenly live ten times as long as your twin sister, just because you respond differently to the social environment. How can that be explained?鈥� says Florian Wolschin at Arizona State University in Tempe. What鈥檚 more, some bees can actually reverse the ageing process. For example, when an older worker bee is forced to switch from foraging to nursing 鈥� a job typical of a younger bee 鈥� it grows physiologically younger in some aspects of protein expression.
It is only by studying ageing in the wild that we can truly sort out the relative importance of nature and nurture. 鈥淎s with everything in biology, it鈥檚 not about genes or environment, it鈥檚 about how they interact,鈥� says Alastair Wilson at the University of Edinburgh, UK.
For example, a mutation in the daf2 gene dramatically lengthens the lifespan of nematode worms living on agar in the lab but it shortens the lifespan of worms in soil and other realistic substrates. 鈥淚 think that鈥檚 the kind of observation that ought to give us pause,鈥� says Steven Austad at the University of Texas Health Science Center in San Antonio.
So far, though, research on ageing in the wild remains at its earliest stages. 鈥淭his is a time of real transition. Over the next decade, I think you鈥檙e going to see a lot more use of natural populations. I think it can only benefit the field as a whole,鈥� says Ricklefs.
Death 鈥� Delve deeper into the riddle of human mortality in our special report.
