Stinky bacteria

To a hyena, a grass stalk is an olfactory Facebook. He can tell from a sniff which other hyenas are in the area: male or female, young or old, pregnant or lactating. All of these characteristics are recognizable from the scent pastes that their owners rub onto such stalks from a gland under their tails. Many mammals communicate by scent, and scientists have long suspected that the chemicals responsible for this language of signature stinks are not made by the animals themselves, but by symbiotic bacteria that live in scent glands.

Researchers tested this idea with a study of pastes scooped from the glands of anesthetized hyenas in Kenya. They took a survey of the bacterial DNA in each paste, and of volatile fatty acids, a family of pungent chemicals that are largely responsible for the smell. The bacterial and chemical signatures matched each other, suggesting the microbes are producing the odors. Individuals with similar chemicals also had similar profiles of bacteria.

What’s more, the bacterial and chemical signatures also corresponded to key pieces of information hyenas detect from smell: the family or clan they come from, their sex and their reproductive status, the researchers reported online in the Proceedings of the National Academy of Sciences.

Shrinking animals

When Earth warms, mammals shrink. That’s what researchers found when they looked back 56 million years, during a time when global temperatures increased about 6 degrees for a period of 20,000 years. Early horses, for example the now-extinct Hyracotherium, shrunk by about 30 percent, presumably to increase the ratio of skin area to body volume, and thus lose heat more easily. Now, scientists have found that this wasn’t a one-off event. At the November meeting of the Society of Vertebrate Paleontology in Los Angeles, another team of U.S.-based researchers looked at a slightly later but somewhat less severe warming period, which happened about 53 million years ago.

Using molar size as a proxy for body size, the researchers looked at mammals in sediments from the fossil-rich Bighorn Basin of Wyoming. They found that the same thing happened: Mammals, including deer and small primates that resembled today’s lemurs, got small again, with horses like Hyracotherium downsizing by about 22 percent this time. In both cases, the animals rebounded to their previous sizes when the warming episode was over.

ScienceNOW is the online daily news service of the journal Science.