Olfactory Sensitivity for Six Predator Odorants in CD-1Mice, Human Subjects, and Spider Monkeys

• Using a conditioning paradigm, we assessed the olfactory sensitivity of six CD-1 mice (Mus musculus) for six sulfurcontainingodorants known to be components of the odors of natural predators of the mouse. With all six odorants, themice discriminated concentrations ,0.1 ppm (parts per million) from the solvent, and with five of the six odorants the bestscoringanimals were even able to detect concentrations ,1 ppt (parts per trillion). Four female spider monkeys (Atelesgeoffroyi) and twelve human subjects (Homo sapiens) tested in parallel were found to detect the same six odorants atconcentrations ,0.01 ppm, and with four of the six odorants the best-scoring animals and subjects even detectedconcentrations ,10 ppt. With all three species, the threshold values obtained here are generally lower than (or in the lowerrange of) those reported for other chemical classes tested previously, suggesting that sulfur-containing odorants may play aspecial role in olfaction. Across-species comparisons showed that the mice were significantly more sensitive than the humansubjects and the spider monkeys with four of the six predator odorants. However, the human subjects were significantlymore sensitive than the mice with the remaining two odorants. Human subjects and spider monkeys significantly differed intheir sensitivity with only two of the six odorants. These comparisons lend further support to the notion that the number offunctional olfactory receptor genes or the relative or absolute size of the olfactory bulbs are poor predictors of a species’olfactory sensitivity. Analysis of odor structure–activity relationships showed that in both mice and human subjects the typeof alkyl rest attached to a thietane and the type of oxygen moiety attached to a thiol significantly affected olfactorysensitivity.

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