AGING IN REPTILES

Like in fishes, the reptiles appear to show three types of senescence. The African skink, Mabuya buettneri, shows rapid senescence similar t o death at mating observed in Salmon and marsupial mouse. Most of the lizards and snakes undergo gradual senescence comparable to the patter n exhibited by a majority of vertebrates. On the other hand, turtles, tortoises and crocodiles continue to grow throughout life and are thus credited with slow or negligible senescence. Evidences and mechanisms of rapid or negligible senescence in reptiles are still fragmentary a nd unclear. Findings in a few species of lizards (Calotes versicolor) and snakes (Natrix natrix) showing gradual senescence support the conc ept of commonalities in ageing phenomena in vertebrates. an age-relate d increase in the stability of collagen and accumulation of altered en zyme molecules, a decrease in metabolism and response to stress-enhanc ed anti-oxidative defence mechanisms and the nature of responses to ho rmones, restricted diet and lower environmental temperature corroborat e the concept. On the other hand neither the increase in mortality rat e and accumulation of lipofuscin nor the reproductive senility have be en shown conclusively in ageing reptile populations. It is likely that there are multiple mechanisms of senescence in reptiles. Further stud ies on selected species from among the 6,000 living species are necess ary to unravel the phenomena.