A team of biologists has identified the Agouti gene, which could help explain why some mammalian parents exhibit nurturing behaviors while others are indifferent or even aggressive toward their young.
The study, led by researchers at Princeton University and in Nature on Wednesday, focuses on the Rhabdomys pumilioa species of African rat in which males can have very different attitudes after becoming fathers.
In mammals, parental care is mostly provided by females: it is estimated that more than 95% of the almost 6,000 known species depend almost exclusively on their mothers to raise their young. Even in species where males remain present, paternal behavior varies greatly.
In the case of the African striped rat, some males clean their young and protect them from the cold with their bodies; others ignore or mistreat the weakest members of the litter, points out.
To understand the neurological basis of these differences, the researchers recorded the brain activity of males in various situations, with and without calves. They found that activity in the medial preoptic area (MPOA), a brain region already associated with parental behavior in females, increased whenever males encountered offspring. But the intensity of this activation varied: higher levels of activity were associated with caring behaviors, while lower levels coincided with hostility.
The team also concluded that the MPOA is not the only important element. The more careful males showed lower levels of expression of Agouti geneusually associated with metabolism and skin pigmentation, rather than parental behavior. The discovery suggests a new function of this gene in the brain.
The social context also counts. Men who lived alone tended to have lower levels of Agouti than those who lived in groups. In some cases, high levels of Agouti appeared to reduce neural activity in the MPOA. When scientists artificially increased the expression of this gene through gene therapy, previously caring males became less interested in their offspring or more aggressive. Moving males from community environments to isolation conditions naturally dropped Agouti levels and restored interest in offspring.
The authors argue that Agouti may function as an evolutionary mechanism, which helps animals adjust their investment in offspring depending on social competition or population density.
