Is There a Trade-Off between Radiation-Stimulated Growth and Metabolic Efficiency?

Beneficial protective effects may result from an adaptive respose to low dose radiation exposure. However, such benefits must be accompanied by some form of cost because the responsible biological mechanisms are not normally maintained in an upregulated state. It has been suggested that stimulation of adaptive response mechanisms could be metabolically costly, or that the adaptive response could come at a sacrifice to other physiological processes. We exposed developing lake whitefish embryos to a fractionated regime of gamma radiation (662 keV; 0.3 Gy min^-1) to determine whether radiation-stimulated growth was accompanied by a trade-off in metabolic efficiency. Developing embryos were exposed at the eyed stage to different radiation doses delivered in four fractions, ranging from 15 mGy to 8 Gy per fraction, with a 14 day separation between dose fractions. Dry weight and standard length measurements were taken 2-5 weeks after delivery of the final radiation exposure and yolk conversion efficiency was estimated by comparing the unpreserved dry weight of the yolk to the unpreserved yolk-free dry weight of the embryos and normalizing for size-related differences in somatic maintenance. Our results show that the irradiated embryos were 8-10% heavier than the controls but yolk conversion efficiency was slightly improved. This finding demonstrates that stimulated growth in developing lake whitefish embryos is not "paid for" by a trade-off in the efficiency of yolk conversion.