An increase in estradiol facilitates the onset of paternal behavior in the dwarf hamster (Phodopus campbelli).

In the dwarf hamster (Phodopus campbelli), activational effects of testosterone (T) and estradiol (E) in the regulation of paternal behavior have been repeatedly rejected because peripheral concentrations of E do not change across the reproductive cycle of males. Further, castration no affected paternal behavior despite that both T and E concentrations decreased significantly. However, the role of these hormones has not been evaluated in models of castration and hormonal replacement in virgin males. Here, we analysed the effects of E and T in paternal behavior in virgin male dwarf hamster (Phodopus campbelli). Thirty paternal (PAT) males were bilaterally castrated; of them, 10 were implanted with T, 10 with E and 10 males received no treatment. Other 10 PAT males underwent sham-castration. Seventeen aggressive (AGG) males were also bilaterally castrated; of these, 10 AGG received E replacement, 7 were not treated. Other 7 AGG males were submitted to sham-castration. Following treatments, paternal behavior tests were conducted again. T and E levels in plasma were quantified by radioimmunoassay (RIA). The results showed that the treatments did not affect the paternal behavior of males that were initially paternal. Neither castration nor sham-castration surgery affected the behavior of AGG males. However, when these males were treated with E and the concentrations of this hormone increase significantly they became paternal. Our data suggest that an increase in E levels shifted infanticidal behavior to paternal behavior in dwarf hamster.