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African elephant genome suggests they are superior smellers


July 22, 2014 - Sense of smell is critical for survival in many mammals. The ability to distinguish different odors, which is important for sniffing out food, avoiding predators, and finding mates, depends on the number and type of olfactory receptors found in an organism's genome. In a study published today in Genome Research, researchers examined the olfactory receptor (OR) repertoire encoded in 13 mammalian species and found that African elephants have the largest number of OR genes ever characterized; more than twice that found in dogs, and five times more than in humans.

To characterize the olfactory capabilities of different mammals, the authors examined genome sequences from 13 placental mammals and identified over 10,000 OR genes in total. The repertoire of OR genes found in any given species was highly unique - only 3 OR genes were shared and evolutionarily conserved amongst all 13 mammals. Surprisingly, the African elephant had the most extensive olfactory repertoire, with almost 2,000 OR genes. "The functions of these genes are not well known, but they are likely important for the living environment of African elephants," said author Yoshihito Niimura. "Apparently, an elephant's nose is not only long but also superior." Conversely, humans, along with our primate relatives, have much fewer numbers of OR genes compared to all other species examined, possibly as a result of our diminished reliance on smell as our visual acuity has improved.


African elephants use their trunks to smell their surroundings. They have five times more olfactory receptors than humans, and the most of any animal characterized to date. Photo courtesy of Eric Green.

The authors traced the evolutionary histories of OR genes using a novel computational tool to deduce ancestral genes, and then examined their duplication or loss in each species. Some lineages of OR genes greatly expanded in a given species, such as an ancestral gene that has duplicated in elephants, generating 84 distinct genes (humans and other primates only have 1 copy), while other OR gene lineages are completely lost. Each species' unique olfactory repertoire, resulting from hundreds of gene duplications and deletions during evolution, highlights the molecular basis for differences in olfaction across organisms.

"Comparison of the repertoires of OR genes among mammals lets us know the commonalities and differences of olfactory perception, deepening our understanding of the sense of smell in humans," Niimura said.

Scientists from the University of Tokyo contributed to this study.

This study was funded by the Japan Science and Technology Agency (JST) and the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid program.

Media contacts:

The authors are available for more information by contacting: Michiyo Sato, General Affairs Division, The University of Tokyo (koho@ofc.a.u-tokyo.ac.jp)

Interested reporters may obtain copies of the manuscript prior to the embargo via email from Peggy Calicchia, Administrative Assistant, Genome Research (calicchi@cshl.edu, +1-516-422-4012). 

About the article:

The manuscript will be published online ahead of print on 22 July 2014. Its full citation is as follows:

Niimura Y, Matsui A, Touhara K. 2014. Extreme expansion of the olfactory receptor gene repertoire in African elephants and evolutionary dynamics of orthologous gene groups in 13 placental mammals. Genome Res doi: 10.1101/gr.169532.113

About Genome Research:

Launched in 1995, Genome Research (www.genome.org) is an international, continuously published, peer-reviewed journal that focuses on research that provides novel insights into the genome biology of all organisms, including advances in genomic medicine.  Among the topics considered by the journal are genome structure and function, comparative genomics, molecular evolution, genome-scale quantitative and population genetics, proteomics, epigenomics, and systems biology. The journal also features exciting gene discoveries and reports of cutting-edge computational biology and high-throughput methodologies.

About Cold Spring Harbor Laboratory Press:

Cold Spring Harbor Laboratory is a private, nonprofit institution in New York that conducts research in cancer and other life sciences and has a variety of educational programs. Its Press, originating in 1933, is the largest of the Laboratory's five education divisions and is a publisher of books, journals, and electronic media for scientists, students, and the general public.

Genome Research issues press releases to highlight significant research studies that are published in the journal.

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