A specialization of taste aversion learning during suckling and its weaning-associated transformation.

During ontogenesis, altricial mammals advance through different ecological niches which require correspondingly different adaptive strategies. We view learning as an important feature of ontogenetic adaptations and consider the acquisition and expression of taste aversion learning during nursing within this framework. Fifteen-day-old preweanling rat pups fail to acquire conditioned taste aversions while nursing, whereas 20-day-old weanlings readily learn flavor aversions while suckling (Martin & Alberts, 1979). The developmental emergence of taste aversion learning while nursing coincides with reduction in maternal milk supply and the rat pup's transition to a solid food diet. We considered the ontogenetic transformation of learning while nursing as a feeding-related adaptive strategy of the weanling rat and tested two predictions derived from this view: (1) delayed weaning might postpone acquisition or expression of suckling-related taste aversions and (2) conditions that permit weaning (e.g., access to alternate food sources) might induce acquisition or expression of such taste aversions. Both predictions were confirmed.