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First published online August 17, 2007
Journal of Experimental Biology 210, v (2007)
Copyright © 2007 The Company of Biologists Limited
doi: 10.1242/jeb.001081
Outside JEB |
AGING SNAKES
Veterinary University Vienna Teresa.Valencak{at}vu-wien.ac.at
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Things wear out with use, and the more intensely we use them, the faster they wear out. This is certainly true for cars, shoes and other objects in our modern world, and might also be true for mammals. About 100 years ago, the German physiologist Max Rubner applied this principle to the aging process in mammals and postulated a negative relationship between an animal's energy turnover and its rate of aging. This `rate-of-living' theory agreed with the `free-radical' theory of aging, which suggested that oxidative stress was caused by the by-products of respiration, reactive oxygen species (ROS). Oxidative stress is higher in animals with higher energy turnover rates and thus could explain why mice live shorter lives than elephants.
Kylie Robert and her colleagues from Iowa State University and Santa Clara University, California, recently tested how aging and lifespan are related to physiological and behavioural differences in six different species of colubrid snakes: either long-lived, with a lifespan greater than 15 years, or short-lived, with a lifespan less than 10 years. Reptiles are very suitable models to test whether metabolism affects longevity, because they have a low rate of metabolism and age slowly but still exhibit a wide array of life spans ranging from <2 years up to records of 150 years.
First, the team tested the rate-of-living theory in the snakes, measuring their oxygen consumption to assess the animals' metabolic rates. They found no relationship between metabolic rate and lifespan, thus contradicting the theory, because the older animals did not have a lower metabolic rate. Since the relationship between metabolic rate and the aging rate is absent in many comparisons in endotherms, Robert and her collaborators were not too concerned that they missed finding one in an ectotherm.
The team suspected that lifespan could also be related to slithering performance, with faster slitherers being better able to escape predators and therefore live longer. To test this idea, the researchers measured the locomotory performance of long-lived and short-lived snakes by recording their locomotory speed, with the help of photocells, over 1 m on a linear racetrack. Consistent with their expectations, Robert and her team observed that longer-lived snakes had increased locomotory performance compared with shorter-lived species. They concluded that in snakes, behavioral traits like locomotory performance influence the avoidance of predation and may even affect the evolution of lifespan. Besides, they also observed that faster snakes also behaved more aggressively, therefore defending themselves better, which helps them reach a longer lifespan.
Finally they turned their attention to cellular physiology and quantified oxidative stress in the two groups of snakes to find out if the free-radical theory of aging applied in the snakes. They measured production of the ROS hydrogen peroxide in mitochondria, finding that short-lived snakes produced significantly more hydrogen peroxide than the longer-lived species. Together, the group's findings clearly confirm the free-radical theory of aging, with longer-lived species producing fewer ROS and suffering less oxidative stress. The authors explain that their study is the first to address ROS production using reptilian species as the model system and shows that colubrid snakes are promising subjects for aging studies.
References
Robert, K. A., Brunet-Rossinni, A. and Bronikowski, A. M. (2007). Testing the `free radical theory of aging' hypothesis: physiological differences in long-lived and short-lived colubrid snakes. Aging Cell 6,395 -404.[CrossRef][Medline]
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