Determination of age of Polynesian rats (Rattus exulans).

[First paragraph(s)...]
The weight of an eye lens increases along an asymptotic curve throughout the normal life span of many mammals (Lord, 1959; Friend, 1967a). In rats (laboratory R. norvegicus) this increase in lens weight has been found to be largely independent of the nutritional status of the animals. Rats maintained under several controlled diet conditions failed to produce differences in lens weight despite nearly two-fold differences in body weight (Friend, 1967b) although the diets of their mothers during pregnancy and lactation may affect lens weight (Friend and Severingaus, 1967, working on white-tailed deer).
As part of a broad study of Rattus species inhabiting coconut and cocoa plantations in Fiji an ageing technique applicable to the most abundant species, R. exulans was evaluated with the aim of investigating the age structure of field populations.