What’s the News: In the animal kingdom, prey species must follow one rule above all others: keep away from predators. To do this, some animals take chemical cues from the urine they stumble upon. Now, new research
published in the Proceedings of the National Academy of Science has identified a single molecule in the urine of many mammalian carnivores that causes rodents to scurry in fear. This chemical could eventually help scientists understand instinctual behavior in animals. How the Heck:
A research team at the Harvard Medical School analyzed a group of olfactory receptors called trace amine-associated receptors (TAARs). They concentrated on one in particular, TAAR4, which is strongly activated by bobcat urine (sometimes used by gardeners to repel small pests). They found that one specific molecule, called 2-phenylethylamine, is responsible for the TAAR4 reaction.
To see if 2-phenylethylamine is bobcat specific, the team tested urine samples from 38 mammalian species, including servals, snow leopards, giraffes, zebras, and rodents. They found that the carnivores had the highest concentrations of the molecule, with some species, like lions and tigers, producing up to 3,000 times more 2-phenylethylamine than the herbivores.
As a way of checking the role of the molecule, the researchers placed a few drops of lion urine loaded with 2-phenylethylamine in a cage with mice and rats. The rodents avoided that area of the cage. The team then used urine free of the chemical, and found that the rodents had no aversion to it.
What’s the Context:
Scientists have long known that chemical cues can mediate predator-prey interactions, and not just in mammalian species. For example, some salamanders and tree frogs use these cues to detect predatory fish.
Sometimes these the cues aren't enough. The parasitic disease taxoplasmosis can overcome rodents’ instinctual aversion to predatory urine. In some cases, the disease causes mice to actually seek out areas marked by cat urine. The mechanism is still a bit unclear, but scientists believe that taxoplasma does this by affecting dopamine levels in the amygdala.
The exact role of TAARs, first discovered 2001, is also unclear. But, "here we have the first convincing evidence that they might control instinctive behaviour," Anna Menini, president-elect of the European Chemoreception Research Organization in Paris, told Nature.
The Future Holds:
The researchers are working to experimentally show that TAAR4 controls the rodents’ instinctive behavior. They are also trying to pinpoint brain circuits that TAAR4 activates as it responds to 2-phenylethylamine.
Future research needs to explain why carnivores have a higher concentration of the 2-phenylethylamine in their urine. The team suspects that it’s a by-product of meat digestion.
Image: Flickr / goingslo