Pheromones found in a mother's milk may be critical to helping her newborn adjust to its environment. A new study of rabbits shows that pups learn to recognize novel odors only when these odors are associated with a chemical cue that typically signals food and warmth.
Learning about the world by sense of smell is common among infants of many mammalian species. Human babies, for example, show interest in whatever foods their mothers eat when nursing because the foods' aromas are passed on through breast milk. Scientists don't understand, however, just how newborn infants learn to identify these additional smells.
Neuroethologist Gerard Coureaud of Centre National de la Recherche Scientifique, in Dijon, France, and his colleagues wondered if rabbit pups expand their horizons via the mammary pheromone, a pheromone in rabbit milk known to attract the blind tots to their mums. When the researchers exposed 2-day-old rabbit pups to two new odorants, the pups didn't react to either. But when the team repeated the experiment--this time after first introducing the same two chemicals with the mammary pheromone--the pups immediately started moving towards the source of the smells. Their behavior was identical to the way they search for their mother's nipples, the team reports online 10 October in Current Biology.
This study demonstrates, for the first time, that the mammary pheromone helps pups learn other odorants, says neuropsychologist Peter Brunjes of University of Virginia in Charlottesville. "From an evolutionary point of view, this [kind of learning] is a really cool thing," he says. That's because by the time the young rabbits venture out of their nests on their own, they must use the smells they learned from their mother to find food and shelter. Coureaud says that future work is needed to address whether this phenomenon occurs in other mammals.