Does the size of an animal’s nose predict how well it can smell? The answer is, perhaps surprisingly, no; in fact, the nose itself doesn’t do any of the actual odor detection. The nose pulls air past what’s called the olfactory bulb, an extension of the brain with chemical receptors, and it’s the binding of compounds to these receptors that allows one to smell things. The more compounds an animal can tell apart, the better it can smell. Here, scientists trained elephants to indicate whether two things smell different to them; in the process, they discover that elephants are better at smelling than… honeybees! Who knew?
Olfactory discrimination ability of Asian elephants (Elephas maximus) for structurally related odorants.
"Using a food-rewarded two-choice instrumental conditioning paradigm, we assessed the ability of Asian elephants, Elephas maximus, to discriminate between 2 sets of structurally related odorants. We found that the animals successfully discriminated between all 12 odor pairs involving members of homologous series of aliphatic 1-alcohols, n-aldehydes, 2-ketones, and n-carboxylic acids even when the stimuli differed from each other by only 1 carbon. With all 4 chemical classes, the elephants displayed a positive correlation between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length. The animals also successfully discriminated between all 12 enantiomeric odor pairs tested. An analysis of odor structure-activity relationships suggests that a combination of molecular structural properties rather than a single molecular feature may be responsible for the discriminability of enantiomers. Compared with other species tested previously on the same sets of odor pairs (or on subsets thereof), the Asian elephants performed at least as well as mice and clearly better than human subjects, squirrel monkeys, pigtail macaques, South African fur seals, and honeybees. Further comparisons suggest that neither the relative nor the absolute size of the olfactory bulbs appear to be reliable predictors of between-species differences in olfactory discrimination capabilities. In contrast, we found a positive correlation between the number of functional olfactory receptor genes and the proportion of discriminable enantiomeric odor pairs. Taken together, the results of the present study support the notion that the sense of smell may play an important role in regulating the behavior of Asian elephants."
Photo: flickr/Greg George
