Originally published by Company of Biologists, reposted with permission.
The upcoming lunar year is going to be the year of the tiger. One of the tiger’s closest cousins lives in the Himalayas – the snow leopard. Unlike other big cats, snow leopards are usually found in rocky terrains above 5,000 meters in elevation. In comparison, tigers that live in similar regions are typically found at elevations below 3,500 meters. One of the biggest challenges for any species living at high elevations is the scarcity of oxygen in the air. What kind of advantages do the snow leopards have that help them thrive at high altitudes?
To answer that question, let’s revisit a Research Article from 2015, published in Journal of Experimental Biology. The authors of this paper began their research by looking at other mammals. Most mammals can adjust how much oxygen the hemoglobin in their red blood cells can carry based on oxygen concentration in the atmosphere. This plasticity is achieved by adjusting the level of DPG, a compound that wedges into the gap on hemoglobin. It changes hemoglobin’s shape and makes it harder for oxygen to bind to hemoglobin. This process helps the red blood cell to offload the oxygen where needed.
Some high-altitude species adapt to low oxygen level by lowering DPG binding sensitivity, causing oxygen-hemoglobin affinity to increase. The increase will allow them to harness more oxygen from the air. Big cats usually carry a set of mutations that reduces the affinity of their hemoglobin for oxygen, making them poorly adapted to high altitudes.
Perhaps snow leopards lost those mutations that affect oxygen affinity and DPG sensitivity for other big cats? Janecka and colleagues investigated this possibility. They sequenced DNA samples extracted from snow leopard droppings collected in their habitat and compared them with genetic sequences of its close cousins: Leopard, Siberian tiger, African lion, and Jaguar. The researchers were surprised to find that snow leopard has the same mutation that makes other big cats unprepared for the lack of oxygen in the air. On top of that, researchers also examined how well snow leopard hemoglobin binds to oxygen with or without DPG. Unsurprisingly, they found that snow leopard hemoglobin is just as bad at carrying oxygen, and just as unresponsive to DPG, as the other big cats’ hemoglobin.
So, what makes the snow leopard unique? The group offered a few hypotheses about why snow leopards thrive at high altitudes despite their disadvantageous hemoglobin. Some high-altitude thriving animals take faster, deeper breaths, and perhaps the snow leopard is one of them. They may also have bigger lungs than other species. In addition, maybe other factors can affect how well hemoglobin takes up oxygen that the researchers did not examine in this paper. At this time, the reason why snow leopards thrive in such harsh conditions remains a mystery to us.
Original article: here