Wednesday, July 23, 2014

Elephants and Their Noses

According to a recent paper,1 elephants may have a greater ability to differentiate smells than any other species on the planet. The conclusion is inferred from the variety of Olfactory Receptor Genes (OFGs) in the African bush elephant genome. There are many things we might extrapolate from this research and a brief report in Science News summarizes some of them.
"Everyone knows that African elephants boast versatile snouts, which can toss logs, grab food and spray water. But the towering mammals may also be the world’s best smellers, scientists report July 22 in Genome Research. The team found that African bush elephants (Loxodonta africana) carry about 2,000 genes for smell sensors, or olfactory receptors. Olfactory cells reside in the pachyderms’ nasal cavities near the tops of their trunks. Renowned sniffers like rats have around 1,200 olfactory receptor genes and dogs about 800. Humans and other primates possess relatively poor olfactory powers and just one-fifth as many olfactory genes as elephants. The researchers think that as mammal species diverged, the original smell-sensing gene duplicated in elephants. The broad smell palette perhaps explains why aromas can dictate elephant behavior. African elephants can communicate aggression via scents and can use smell to distinguish the Maasai, an ethnic Kenyan group that hunts elephants, from the Kamba, who are primarily farmers and pose no threat."
Questions remain about the functionality of these olfactory receptors in the elephant and there are other contributors to olfactory sensitivity and discernment which will need to be considered. For example, researchers need to look at the amount of olfactory epithelium and the enervation of that tissue in the snout of elephants.2 Gene expression is another important factor and so experiments which differentiate between genes and their function in the elephant's nose will be important next steps in determining the importance of the OFGs. We know that in humans there are genes which code for vestigial olfactory structures which do not contribute to our sense of smell; thus, the extent to which the inferences of this article hold true await further research.



1Niimura, Yoshihito, Atsushi Matsui, and Kazushige Touhara. "Extreme expansion of the olfactory receptor gene repertoire in African elephants and evolutionary dynamics of orthologous gene groups in 13 placental mammals." Genome Research, 2014.
2Bear, Connors and Paradiso, Mark, Barry and Michael (2007). Neuroscience: Exploring the Brain. USA: Lippincott Williams & Wilkins. pp. 265-275.

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