The development of a sex-differentiated defensive motor pattern in rats: Apossible 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 o pposing the other rat's midbody, males typically oppose the head. In this s tudy, two developmental factors were investigated for, their role in the ge nesis of this sex-differentiated motor pattern: (a) Dodging by males and fe males was analyzed before and after puberty to ascertain whether the differ ential pattern of movement was associated with the pubertal change ill pelv ic morphology, and (b) Dodging by adult males and females that had been rai sed without social interaction from weaning was analyzed to ascertain wheth er experience in the juvenile phase of development was necessary. In both s tudies, males and females performed the sex-typical version of the dodging motor pattern regardless of age or test condition. However, orienting to th e head of the opponent was disrupted in males I-cared 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 differentia tion of the motor organization of dodging develops without the need for exp erience, the males' ability to direct this motor pattern with the correct o rientation towards the opponent requires sonic prepubertal experience. (C)1 999 John Wiley & Sons, Inc. Dev Psychobiol 35: 156-164, 1999.