Figure 4.

Dams retrieve males before females because of their USVs. Four-day-old pups were removed from the nest for 5 min and marked to identify sex, then placed back on the opposite side of the home cage as shown in panel 1. The dam retrieved the pups one by one as shown in panel 2 (A). The rank order sum quantification of pup retrieval based on sex in control dams with litters that received no treatment indicated male pups were more likely to be retrieved before females (Mann–Whitney U = 36.0, p < 0.05, B, based on 6 litters). When litters were treated with either siRNA against Foxp2 or scrambled control (C), control males were again significantly more likely to be retrieved first and females retrieved last. Males treated with siRNA against Foxp2 were significantly less likely to be retrieved compared with control males, whereas females treated with Foxp2 siRNA, which have USVs similar to control males (Fig. 1A) were significantly more likely to be retrieved before control females (Kruskal–Wallis test = 20.5, p < 0.05, groups with the same letter are significantly different from each other (C, based on 5 litters).