Elephants trump the sniff charts with the strongest sense of smell identified in a single species so far, a new study has found.
Published in the journal Genome Research, new data has revealed that African elephants possess the largest number of genes associated with smell documented to date, donning five times as many as humans and twice as many as dogs. To their surprise, they even beat the previous record holder, rats.
For the study, researchers compared the genomes of 13 different placental mammal species including elephants, horses, rabbits, rodents and orangutans. They were looking specifically at genes encoding olfactory receptors (ORs). ORs reside in the airways and bind to odor molecules. A signal is then sent to the brain for interpretation via olfactory receptor neurons.
They found that the number of OR genes varied significantly between the different animals, ranging from 296 in orangutans to almost 2,000 in African elephants. Furthermore, they found that the common ancestor of all the species investigated had 781 genes, suggesting that while primates had lost a number of OR genes, elephants and rodents had gained genes over time.
Mistakes in DNA replication can lead to both the duplication of genes and the loss of genes. If duplicated genes subsequently acquire mutations then they can eventually become distinct from the original gene.
According to lead author Yoshihito Niimura, the relatively low number of genes found in primates could be due to a diminished reliance on smell as vision improved.
Having such a large repertoire of OR genes likely assists the elephants in locating food and avoiding predators. For example, a 2007 study found that African elephants are able to distinguish members of two different tribes living in Kenya based on both smell and color cues. Young members of one of the tribes, the Maasai, kill elephants in order to prove themselves as a male, whereas the other tribe, the Kamba, usually do not hunt them.
Furthermore, according to biologist Bruce Schulte, who was not involved in the study, research has suggested that male elephants may use their acute sense of smell in order to determine when a female is ready to reproduce. This would be advantageous since elephants only have a small window of opportunity to reproduce every few years, Live Science reports.
While the researchers did not assign functions to all of the genes identified, they extrapolate that the vast number present likely bestows a keen sense of smell.
"Apparently, an elephant's nose is not only long but also superior," said Niimura.
[Via AFP, Live Science and Genome Research]