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Exclusively inhabiting tropical countries such as Senegal, wild chimpanzees lack adaptations to seasonal variations in ultraviolet B (UVB) irradiance from sunlight; since UVB exposure enables vertebrates to synthesize vitamin D, Sophie Moittié and colleagues studied zoo chimpanzees in Italy and other mid-latitude countries to see how vitamin D levels are affected by the seasonal variations in UVB irradiance that occur in those locations. They found that chimpanzees’ vitamin D levels were significantly lower in winter than in summer and appeared unaffected by oral supplementation of vitamin D administered by zookeepers. Moittié and colleagues point out, however, that supplementation was rare, highly varied, and poorly tracked, and therefore they caution against concluding that       

Which choice most logically completes the text?

A

vitamin D levels among zoo chimpanzees in Italy and other mid-latitude countries likely show different seasonal patterns than do vitamin D levels among wild chimpanzees in Senegal and other tropical countries.

B

the lack of an observed effect of supplemental vitamin D on zoo chimpanzees in Italy and other mid-latitude countries may reflect shortcomings in the data rather than actual ineffectiveness.

C

providing zoo chimpanzees in Italy and other mid-latitude countries with supplemental vitamin D has no promise as a strategy for offsetting winter reductions in their vitamin D levels.

D

winter reductions in UVB irradiance in Italy and other mid-latitude countries can contribute to variations in zoo chimpanzees’ vitamin D levels.