The University of Southampton

How some plants and animals appear to defy the ageing process

14 January 2008

The inevitability of the ageing process and the onset of senescence - the process of deterioration with age - is a fact of life for most plant and animal species.

Some, however, live to extreme ages, such as the English yew, of which at least one alive today is recorded in the Domesday Book; while a few organisms seem to defy current evolutionary understanding altogether, by appearing to have indefinite generation lengths with negligible senescence. For example, the Rocky Mountain Bristlecone Pine is known to produce viable cones at over 4000 years of age.

New research by ecologist Dr Patrick Doncaster from the University of Southampton, and mathematician Professor Robert Seymour from University College London, demonstrates the principle by which some organisms can indefinitely postpone the onset of senescent ageing.

'Our analysis indicates that sedentary organisms, including some types of tree, are particularly likely to achieve this postponement of the onset of senescent ageing,' comments Dr Doncaster. 'It evolves through many generations of ancestors "crowding out" young individuals of the same species that attempt to grow to adulthood alongside them.'

He continues: 'The inevitability of senescence amongst organisms with repeated reproduction has well-developed theoretical foundations. In essence, since reproduction carries physiological costs, natural selection favours reaping early benefits, and delaying the cost in physiological decline until later in life when there is a greater chance of being dead anyway from environmental hazards.

'But some organisms show negligible senescence and a few, such as Hydra, which is a very simple freshwater animal, and the Bristlecone Pine, appear to have indefinite generation lengths. We have now answered the question of how they could have evolved from ancestors with senescent life histories. Mathematical analysis shows that the crowding out of young individuals favours selection on ever-reducing senescence. Our computer simulations indicate that this runaway process could even lead to immortality.'

The research paper 'Density Dependence Triggers Runaway Selection of Reduced Senescence' is published in PLoS Computational Biology, the official journal of the International Society for Computational Biology.

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