The researchers found that the absence of progesterone's actions reduced aggression while promoting positive paternal behavior. The findings, to be published online by the Proceedings of the National Academy of Sciences during the week of Feb. 24, suggest a new approach to studying an area of biology that has been poorly understood.
"We discovered that the hormone progesterone and its receptor are important in males, not just females," said Jon E. Levine, professor of neurobiology and physiology, who led the provocative study. "Paternal behavior may be based in the same biology as maternal behavior."
Like adult males of many other species, male mice rarely contribute to parental care and often attack or kill infants soon after birth. Although this hostile behavior had previously been attributed to testosterone, a correlation between testosterone and male behaviors directed at young has never been established. Seeking another explanation for the male behavior, Levine's research team tested paternal behavior in progesterone receptor knockout mice. (These mice lack the gene that encodes progesterone receptors and thus the animals are not affected by the presence of progesterone.)
"In male knockout mice we noticed something quite startling," said Levine. "They behaved differently, and the most obvious changes were a complete lack of aggression toward infants and the emergence of active paternal care. These animals are terrific dads."
After breeding males of both the knockout and a control strain, the researchers found a complete absence of infanticide in the resulting litter
Contact: Megan Fellman