The development of a sex-differentiated defensive motor pattern in rats: A possible role for juvenile experience

When protecting a food item held in the forepaws, rats will dodge laterally away from an approaching conspecific. Both males and females dodge, but do so differently, with females pivoting around the pelvis and males pivoting around the midbody. While females tend to end the dodge with their rumps opposing the other rat's midbody, males typically oppose the head. In this study, two developmental factors were investigated for their role in the genesis of this sex-differentiated motor pattern: (a) Dodging by males and females was analyzed before and after puberty to ascertain whether the differential pattern of movement was associated with the pubertal change in pelvic morphology, and (b) Dodging by adult males and females that had been raised without social interaction from weaning was analyzed to ascertain whether experience in the juvenile phase of development was necessary. In both studies, males and females performed the sex-typical version of the dodging motor pattern regardless of age or test condition. However, orienting to the head of the opponent was disrupted in males reared in social isolation, a feature of dodging that developed between weaning and puberty. Therefore, the evidence is consistent with the view that while the sexual differentiation of the motor organization of dodging develops without the need for experience, the males' ability to direct this motor pattern with the correct orientation towards the opponent requires some prepubertal experience.