"We see this fierce protection of offspring is so many animals," says Stephen Gammie, a University of Wisconsin-Madison assistant professor of zoology and lead author of the recent paper. "There are stories of cats rescuing their kittens from burning buildings and birds swooping down at people when their chicks are on the ground."
In terms of biology, it makes sense that mothers would lay down their own lives to protect their offspring, especially if it means the parents' genes will be passed down to the next generation, says Gammie. But he adds that despite all the observations and the theories explaining why mothers display this behavior - commonly known as maternal aggression - very little research has investigated the biological mechanisms that turn on this trait in new mothers.
"We've known for a long time that fear and anxiety decrease with lactation," explains Gammie. "Maybe it's this decrease that allows mothers to attack during a situation that normally would evoke a fear response."
Testing this hypothesis, the Wisconsin professor and his colleagues studied the link between maternal aggression in mice and levels of corticotropin-releasing hormone (CRH), a peptide that acts on the brain to control behavior.
About six days after a group of mice gave birth, the new mothers received injections containing either one of three doses of CRH or a saline solution with no amount of the peptide. Following each injection, which was given once a day for four consecutive days, the researchers returned the mother mice to their pup
Contact: Stephen Gammie
University of Wisconsin-Madison