Sentence:  Reindeer are well suited to the taiga's frigid winters. They can <WSD>maintain</WSD> a thermogradient between body core and the environment of up to 100 degrees, in part because of insulation provided by their fur, and in part because of counter-current vascular heat exchange systems in their legs and nasal passages. 
Meaning of the word marked with <WSD> tags:  To keep up; to preserve; to uphold (a state, condition etc.). (from 14thc.)