But if there truly is such a compensation, then doesn't that demonstrate that low levels of radiation are beneficial to at least one type of mammal? It is currently presumed that less radiation exposure is always better. This study seems to provide evidence to suggest that is not a universally valid claim.
Your point is well taken. However, my point is the perceived benefits are to a species that receives very little radiation to start with. Most mammals are daily exposed, and have adapted to, radiation from the sun. The voles spend most of their time in darkness. By the same token, I suppose blind creatures that live in caves, such as certain fish and insects, would benefit from exposure to radiation. They would either develop the ability to see or perish.