How the animal kingdom can inspire us to live for longer

Published on Friday 10 July 2009 20:07

SCIENTISTS at three Scottish universities are leading a research effort aimed at understanding how and why some kinds of animals have the capacity to live so much longer than others.

Ageing research traditionally focuses on a narrow range of species, thought to offer good models of fundamental ageing processes common to most organisms.

But the Scottish researchers think we might be missing a trick by not finding out more about lifespan diversity.

Natural variations in lifespan are truly remarkable. Most people know big animals, such as elephants, usually live longer than small animals like mice, and cold-blooded animals such as reptiles and fish generally have much longer lives than warm-blooded birds and mammals.

But how many realise that the maximum lifespan of a bird is on average three times that of a mammal of the same size?

Pet parrots regularly outlive their owners, but even common birds, such as starlings, have been recorded as living for more than 20 years. A similar-sized mammal would have a maximum lifespan of two or three years, yet birds' physiology would indicating otherwise.

Birds typically have high body temperatures (40C to 42C), high metabolic rates, rapid growth rates and high blood glucose levels, all traits that we would expect to result in shorter, not longer, lives.

In general, rates of ageing and maximum lifespans are a consequence of the balance between factors that damage the body, and the extent to which damage is repaired.

Much of the damage comes about through oxidation of bio-molecules by highly reactive free radicals. The more energy expended in fuelling growth and reproduction, and in fighting off disease, the greater the exposure to internally generated free radicals.

Animals have evolved a range of antioxidant defence mechanisms to prevent and repair such damage The balance of damage and repair in different species depends, crucially, on the extent to which they can produce more young by being big, reproducing fast or living a long time.

With the focus on small and large mammals in Aberdeen and Edinburgh respectively, and birds and fish in Glasgow, the groups are investigating the great diversity in the pace of ageing.

Importantly, research shows long-lived animals in the wild do show clear signs of ageing. Older individuals reproduce less well and their survival is lower than when in middle age.

Work in Glasgow and Edinburgh with long-lived seabirds and wild mammals, such as red deer, has shown that both genes and early life conditions play important roles in how fast individuals decline. It also seems that, although their physiology runs faster, birds take other things in life, such as reproduction, more slowly than mammals.

But longevity is not simply a matter of the pace of energy expenditure. The Aberdeen group found that raising an animal's energy expenditure does not necessarily shorten its life and can increase it, possibly by making its antioxidant defences more effective.

When it comes to degeneration and repair at cellular level, important differences between us and other species are being uncovered. One interesting factor is the pattern of loss of special bits of DNA that protect the ends of chromosomes, known as telomeres. Every time cells divide, these get shorter and the loss increases with more exposure to damaging free radicals. Evidence is mounting that comparing telomere lengths between individuals of the same species is a useful indicator of biological state. Wrinkles, baldness or grey hair are not indicators of likely remaining lifespan; how short your telomeres are might well be.

In humans, average telomere length gets shorter with age and under high stress, and this had been linked to life expectancy.

The Glasgow group has shown this link to life expectancy occurs in wild birds, but, importantly, telomere length and age do not seem to be closely linked in long-lived birds. How this occurs is under investigation.

Studying the diversity of solutions evolved by animals in which a long lifespan has been favoured by evolution might uncover novel mechanisms that could help us to hold back the march of time in our own species. Evolution geared us to maximise lifetime reproductive success, which is influenced by reproductive rate and lifespan, but we now want to maximise only our life.

Other species, with different evolutionary pressures to us, might just have some clever physiological tricks to help us in this quest.

&#149 Pat Monaghan is professor of environmental and evolutionary biology at Glasgow University. She has been seconded to The Scotsman as part of the British Science Association's Media Fellowship scheme, which promotes a greater understanding of the media among scientists.