Testosterone promotes 'cuddling,' not just aggression

Aubrey Kelly et. al conducted experiments on Mongolian gerbils, rodents that form lasting pair bonds and raise their pups together. While males can become aggressive during mating and in defense of their territory, they also exhibit cuddling behavior after a female becomes pregnant, and they demonstrate protective behavior toward their pups.

In one experiment, a male gerbil was introduced to a female gerbil. After they formed a pair bond and the female became pregnant, the males displayed the usual cuddling behaviors toward their partners. The researchers then gave the male subjects an injection of testosterone. They expected that the resulting acute rise in a male's testosterone level would lessen his cuddling behaviors if testosterone generally acts as an antisocial molecule.

"Instead, we were surprised that a male gerbil became even more cuddly and prosocial with his partner," Kelly says. "He became like 'super partner.'"

In a follow-up experiment a week later, the researchers conducted a resident-intruder test. The females were removed from the cages so that each male gerbil that had previously received a testosterone injection was alone in his home cage. An unknown male was then introduced into the cage.