First, with regard to aging of wild rats:
I agree that there is no way to obtain an exact age of wild
species because of individual variablity. I will mention,
however, a correlate that I have not seen mentioned by others
and that is cross-linking in the extracellular matrix. A paper,
discussing this in human's is :
Sell, DR, and Monnier, VM. Structure elucidation of a Senescence
cross-link from human extracellular matrix. J. Biol. Chem. 266:
21597-21602, 1990.
This process also occurs over the life-time
of the primitive least shrew (Orin Mock, Ph.D., Personal
Communication). I don't know for sure, but presume it also
occurs in more advancd rodents like the rat.
Second regading nutrition and aging:
Several contributors have asserted recently that eating well
is associated with an increased life span. There is a wealth
of experimental evidence to suggest exactly the opposite.
That is, caloric restriction has been shown to promote longevity
in experimental animals. A place to start reading about this
might be:
YU, BP, How diet influences the aging process of the rat. Proc.
Soc. Exp. Biol. Med. 205: 97-105,1994.
Clearly, starvation hastens death; but so too does overeating
hasten death.
I'm headed home to dinner now!! Oh well.
