Â鶹ÒùÔº

Animals living at higher elevations found to have decreased sense of smell

A recent study in Current Biology has found that animals living at elevations of 1,000 meters and higher have a reduction in genes related to smell and a smaller olfactory bulb than similar low-altitude species.

The researchers screened the genomes of 27 different species of animals living in high-altitude environments, as well as their low-altitude relatives. A wide range of mammal types was studied, including monkeys, goats, llamas and guinea pigs. Both domesticated and wild mammals were included.

Scientists found a 23% reduction in genes related to smell and an average of an 18% size reduction of the olfactory bulb, a kind of smell processing center located in the brain. These evolutionary changes appear to be specific to smell. No changes were found in the genes related to pheromone and taste detection.

Environmental differences at high altitudes include thinner, drier and colder air, which can lead to difficulties in breathing, increased nasal congestion and hypoxia—low levels of oxygen in the body. These conditions also make it harder for scent molecules to travel—meaning there are fewer available scents for animals to detect in the air.

Although the exact mechanism is still unclear, the reduced sense of smell may be related to the reduction of available scents and to nasal inflammation, which causes additional difficulties in picking up scents. Over time, these issues may have led to mountain-dwelling animals evolving a worse sense of smell, but possibly compensating with better vision or other senses. However, additional studies would be needed to determine whether the loss of smell resulted in other increased abilities or senses.

The study also compared the genomes of human communities at high and low altitudes. Researchers studied the genomes of Tibetans, who were estimated to have established their mountain-dwelling communities at altitudes above 3,000 meters sometime between 9,000 and 30,000 years ago. These were compared with the genomes of the low-altitude Han Chinese populations.

Interestingly, no olfactory changes were found in human populations. Researchers posit that this may be due to the continued mixing of lowland and highland populations, or because there may not have been enough generations for the genetic changes to occur yet.

This research provides a novel twist on prior studies of the effects of high-altitude living. Prior studies have mostly focused on adaptation by gaining new functions or traits to cope with harsh environments, while this study shows that animals can also lose certain abilities. These understudied mechanisms of maladaptation and trait loss may have future implications for evolutionary biology and medicine.