BIOLOGY OF RODENTS 



211 



TABLE 7 



Summary of Ambient and Rat-Implanted Dosimeter Exposure 

 Results, Enewetak Atoll, November 1977 to April 1978* 



Ambient dosimeters, 

 exposure (mR day ') 



Implanted dosimeters, 

 exposure (mR day^') 



'Dosimeters supplied and analyses provided by I Aoki, Radiological and Environ- 

 mental Sciences Laboratory, Idaho Operations Office, DOE. Calculated results in mil- 

 lirem (mR) were derived for total exposure [seriod. 



tToo low to calculate. 



in these vegetation piles. Burning, however, was incom- 

 plete; resprouting of shrubs occurred rather quickly. The 

 rats increased in numbers and began to spread. 



The bulldozing of transects for radiation measurements 

 on other islets probably had limited impact on the rats. 

 The brush piles provided increased harborage; certainly, 

 the carrying capacity of these islet habitats for rats was 

 not decreased. 



In our earlier studies, we had found no abnormalities in 

 rats that we could associate with elevated radiation levels. 

 The rats were not larger, nor did we observe a greater 

 prevalence of tumors or resorbed embryos. Color phases 

 were not associated with radiation patterns. The melanistic 

 roof rats on Runit are better explained through genetic 

 drift in an isolated population. In recent studies, however, 

 Temme (1981, 1986; Temme and Jackson, 1978) found a 

 positive relationship between background radiation levels 

 and frequency of palatal ridge deviations in the roof of the 

 mouth (Figs. 5 and 6). For example, the incidence of 

 abnormal palatal ridges was 0.44 in Polynesian rats from 

 Lujor Islet, which had the highest test contamination of 

 islets still harboring this species. On Japtan, with no direct 

 testing contamination, the incidence was 0.06. Other popu- 

 lations were intermediate, but similar relationships were 

 not evident in roof rat comparisons. 



However, when mean measures of divergence for 

 palate ridge variation are compared, values between 

 Enewetak and Bikini Atolls and between Enewetak and 

 other atolls are much larger than statistics comparing the 

 north end of Enewetak Atoll (greatest radiation exposure) 

 with the southerly islets (least exposure) (0.75 to 2.0 vs. 

 0.20 to 0.35) (Figs. 7 and 8). Thus these palate variant 

 patterns also may be influenced by geographic isolation — 

 the greater the geographic separation, the larger the diver- 

 gence statistic (Temme, 1981). As far as could be deter- 

 mined, these slightly altered palatal ridge structures cause 

 the rat no difficulty; we do not know if a mutation is 

 involved. 



Plasma transferrins were examined by Malecha and 

 Tamarin (1969) from roof rats collected on Runit, Enjebi, 

 and Medren. Five alleles were found, compared to only 



A 



12 3 4 5mm 



I — ■ — ■ — ■ — ■ — I 



papilla palatina (^fc^ 



diastemal or 



antemolor 

 ridges 



\.v 



intermolar ridges ii^fA/''' "SJ 



— till >'*''V,. Lin 



gulor pad 



B 



5 mm 

 ' ' (^ 29.77, 



^11.6 7. 



Fig. 5 a. Nomenclature of palatal ridges in typical Polynesian 

 rat; b. Incidence of diastemal ridge deformation in rats on 

 Lowja (Enewetak Atoll), which had intermediate levels of 

 background radiation, was 0.30. On Japtan (outside the con- 

 taminated area) the incidence was 0.02. A new aberration, 

 involving intermolar ridges and found in 1256 of the speci- 

 mens, was unique to Japtan (Temme and Jackson, 1978). 



