Underground Popeye. Blind mole rats are more efficient than other rats at getting oxygen to where they need it--their muscle-bound forearms.

You Dirty (Oxygen Deprived) Rat

Like a miner in a collapsed shaft, the blind mole rat often finds itself digging in tunnels with scant oxygen. Now scientists have a better idea how this animal survives down under: It's more efficient at getting oxygen to its muscles than other kinds of rats are. The finding, reported in the current issue of the Proceedings of the National Academy of Sciences, sheds light on how species evolve to cope with hostile environments.

Physiologist Ewald Weibel of the University of Bern in Switzerland and his colleagues have been studying how species such as the pronghorn antelope and the tiny Eutruscan shrew have developed specialized physiology for their environments. So they wondered if the blind mole rat (Spalax ehrenbergi superspecies), which is found in Israel, also has developed unique physiology for its oxygen-poor environment. "Mole rats have to work very hard to dig their burrows," Weibel says. "It's an extreme constraint."

Unlike naked mole rats, which are selfless critters that live in beehivelike communities, blind mole rats are rugged individualists. Weibel, who obtained several specimens from the dean of blind mole rat studies, Israeli comparative physiologist Eviatar Nevo, admits to being a bit put off by the hirsute creatures when they first appeared in his lab. "They're vicious and have enormous teeth," Weibel says. But the cruel exterior belies a fragile nature: "We had to struggle to keep them alive."

Weibel's group ran the mole rats on a treadmill and put them through a battery of other tests to measure oxygen consumption and diffusion to the muscles. Compared to white rats, they found, the mole rats had about a 30% greater capillary density in the muscles. And while mole rats have less muscle mass than ordinary rats, they have almost 50% more mitochondria, organelles that process oxygen, by volume of muscle tissue. Moreover, the mole rats are like miniature Popeyes: "Almost all their muscle mass is in the front of their body," Weibel says, which enables the mole rat to use its forearms "like a powerful shovel."

Mole rat experts give Weibel's study thumbs up. "In my opinion, the work is interesting and novel," says Chris Faulkes of the Institute of Zoology in London. Faulkes, a specialist in African mole rats, cautions that findings from Spalax cannot necessarily be generalized to other species.