Elephants have the most discerning sense of smell of any mammal, according to a new study.
The quantity and type of receptor genes in the nose of elephants provides this acute abilities to pachyderms. These genes, designed to detect smells, are utilized in sensor cells that line the nasal cavity of the animals, called the olfactory receptor (OR) repertoire. When an odor triggers these cells, a stream of nerve signals travels from the nose to the brain. Here, the animal interprets the signal as a particular odor.
Smell is essential to animals in the wild. They are used to find food, detect which foods may not be healthy, and to discover mates.
Researchers examined the OR structures of 13 different types of mammals, including humans. Other animals examined included guinea pigs, rabbits, cows, rodents, chimpanzees and horses.
They found elephants possess more OR genes than any species ever recorded. This was twice as high as dogs, well known for their sense of smell. Our own species was found to have only 400 types of the olfactory receptors - roughly 20 percent as many of the genes as pachyderms.
More than 10,000 different OR genes were examined during the study. Elephants possess about 2,000 of the organic structures. Canines have around 1,000. Only three of the genes were common to all 13 species.
"The functions of these genes are not well known, but they are likely important for the living environment of African elephants. Apparently, an elephant's nose is not only long but also superior," Yoshihito Niimura, study co-author, said.
An earlier study showed elephants are nearly as good as mice at identifying individual smells. The tiny rodents have almost 1,300 varieties of the genes in their noses, providing a great deal of discrimination between odors.
Elephants have learned to use their sense of smell to distinguish one group of people from another. Some of the Maasi people, nomads who live in southern Kenya and northern Tanzania, will try to spear the behemoths. The Kamba, other Kenyan natives, rarely hunt the animals. Using their large repertoire of OR genes, elephants in the area are able to determine the level of danger presented by encroaching humans.
The low number of OR genes in humans and chimpanzees may be due to our visual acuity. Some researchers believe we lost much of our olfactory discrimination as eyesight become more important among our distant ancestors.
The repertoire of smell present in any given species is determined by the constant duplication of genes. Over the course of millions of years, OR genes can appear and disappear, affecting nasal skills.
Study of elephants and their olfactory abilities was detailed in the journal Genome Research.
