TRAINOR, B. C.; MARLER, C. A.: Testosterone promotes paternal behaviour in a monogamous mammal via conversion to estrogen

Typically thought of as a hormone that inhibits paternal behavior, recent correlational and hormone manipulation studies have found that testosterone (T) could actually promote paternal behaviors in mammals. Here we show that in the California mouse, Peromyscus californicus, T promotes paternal behaviors via aromatization to estradiol (E₂). In the first experiment, castrated males given T or E₂ implants showed significantly higher levels of huddling and pup grooming behavior than males given dihydrotestosterone or empty implants. In the second experiment, castrated males treated with T implants and an aromatase inhibitor (fadrozole) showed significantly lower levels of huddling and pup grooming behavior compared to castrated males treated with T implants and inhibitor vehicle. Brain areas that are known to promote or inhibit parental behavior contain high levels of aromatase in the males of many mammalian species. One possible explanation for these results is that T is aromatized in brain areas such as the medial preoptic area or the medial amygdala, where E₂ then has effects on behavior.