Response of Wild Rodents to Acute Gamma Radiation

Recent reports have shown that some species of small wild rodents, pocket mice (Perognathus longimembris and Perognathus formosus) (1) and cotton rats (Sigmodon hispidus) (2), given an acute dose of y-radiation have an LD50o(3o) that ranges between 1200 and 1500 r. This level of lethality is considerably higher than that of the laboratory mouse (544 to 665 r) (3) and the laboratory rat (665 r) (4), animals of approximately the same body size as the pocket mouse and cotton rat. Since it has been suggested that resistance to radiation is a criterion of general fitness (5), it might be concluded that wild rodents that are genetically diverse and as adults have passed through a period of rigorous natural selection are more fit and also more resistant than laboratory rodents. Alternatively, these data may represent exceptional species. Our studies have been designed to obtain evidence on these questions of comparative radiation sensitivity. Since a large number of variables such as age, sex, kind and intensity of radiation, previous treatment, length of time in captivity, genetic background, and environment affect lethality and make comparison of the results from different experiments and laboratories difficult, the procedure in these studies has been to collect adult wild small mammals by live-trapping and to compare their response to acute y-radiation with that of domestic mice under both laboratory and field conditions. Where possible, both wild and domestic forms of the same species have been used. In the laboratory experiments the wild mammals must adjust to the unusually stabile laboratory environment; in the field experiments the domestic mammals must adjust to a constantly fluctuating environment. Thus, the experimental design compares wild and domestic forms within a species and between