By flipping a molecular switch, males go from being puppy guardians to being puppy killers
The difference between a loving father and a deadbeat may come down to a molecular switch in the brain – at least in African striped mice.
Stimulate the activity of a particular gene in a part of the brain known to regulate maternal care transformed the nurturing males into distant males and even, in certain cases, in the killers of mouse pups, researchers report on February 18 in Nature. The findings reveal how social context can change gene activity in the brain and thus shape the care provided to men.
The provision of care to men is widespread in fish and amphibianswhich suggests that this is a very ancient behavior among vertebrates. Among mammals, however, fewer than 5 percent of species have fathers who stay behind to raise their young. Male African striped mice (Rhabdomys pumilio) are one of the exceptions to the rule, although their dietary tendencies vary greatly, making them an ideal species to study the factors that influence this behavior.
Some take care of young people and care for them; others ignore the puppies or even attack them. The same male could become aggressive or doted on.
To understand this behavior, comparative neurobiologist Forrest Rogers and his colleagues observed the mice’s social environment. In laboratories, group-housed males tended to be aggressive toward mouse pups when introduced to them. But surprisingly, when these males were moved to be housed alone, they became very paternal.
“I clearly thought something was wrong, because all the work we know about mice and rats is that if you isolate them socially, they become very anxious and are often not the most caring individuals,” says Rogers, of Princeton University. But the lone male African striped mice didn’t seem anxious at all.
The researchers photographed the brains of the males to identify the regions activated by interaction with the young. Good caregivers showed greater activity in the medial preoptic area, or MPOA, than hostile males. This region of the brain was previously known to be rewired in new mothers of other rodent species.
“A lot of the neural responses…that are starting to be so well documented in maternal behavior, these same brain regions are at work in males as well,” says Sarah Hrdy, an anthropologist at the University of California, Davis, who was not involved in the new study.
But when the team delved deeper into the molecular level, they had a surprise: a gene called Agouti was more active in the MPOA of aggressive males.
Artificially boost the activity of Agouti in the MPOA have become previously ambivalent nurturing and sometimes infanticidal males. But when men moved from a communal lifestyle to a solitary lifestyle, Agouti the levels in their brains dropped and they became more interested in taking care of the puppies.
Agouti was previously known to be important for the development of the characteristic mouse stripes. So its involvement in the brain “was a big surprise, honestly,” says Ricardo Mallarino, a developmental and evolutionary biologist at Princeton whose previous work revealed how the African striped mouse got its stripes.
“This animal has developed the ability to assimilate information from its environment and regulate its behaviors which are often energetically demanding,” explains Mallarino. The activity of Agouti in the brain, it’s how the mouse integrates signals about the social environment to balance competing demands, such as parenting, feeding, and defending territory.
Taken together, the findings support a growing body of research showing how the social environment can change gene activity in the brain, which in turn affects parental behavior.
It’s unclear if something similar happens in humans. Unlike the apes we are closest to, many human fathers care for babies. We are only beginning to explore the potential biological roots of this behavior. “We are in the early stages of understanding the nurturing potential of humans,” says Hrdy.
