Motor competition in the prenatal ontogeny of species-typical behaviour

Abstract

Facial wiping, an action pattern antecedent to grooming behaviour in adult rodents, can be elicited during the prenatal period by infusion of a lemon solution into the mouth of the fetal rat, Rattus norvegicus. In altricial species such as the rat, the wiping response to chemosensory infusion temporarily disappears during early postnatal development. The expression of facial wiping may be constrained by features of the postnatal environment, or may be suppressed through competition with incompatible motor responses. To test these alternative hypotheses, a comparative study of altricial and precocial rodent fetuses was conducted. Fetuses of two altricial species, Norway rats and Mongolian gerbils, Meriones unguiculatus, expressed the wiping response during the last 1–2 days of gestation. In contrast, fetal cotton rats, Sigmodon hispidus, and spiny mice, Acomys cahirinus, exhibited accelerated emergence followed by prenatal disappearance of the wiping response, which is consistent with a motor competition hypothesis. The age at which the wiping response disappeared coincided with the emergence of contact righting and quadrupedal locomotor behaviour, which appear to interfere with the expression of facial wiping.