An Analysis of Habitat Preference in Mice as a Function of Prior Experience

This study was designed to explore various aspects of the role of learning in determining habitat preference in mice. Using an inbred strain of mice, a series of six experiments was conducted in order to evaluate the effects of experience with two different bedding materials upon bedding material preference. Bedding preference was examined in various experiments by allowing a choice of bedding material and noting on what material the animal slept, ate and where females maintained their litters. In addition, growth and reproductive indices as a function of bedding experience were also recorded. Experiment I was designed to answer basic questions about the role of prior experience in determining habitat preference in mice. Variations in the bedding material to which mice were exposed were found to affect their habitat preference at weaning and in adulthood. In addition, it was found that prior experience had different effects on the habitat preference of male and female offspring. Males, rather than females, demonstrated a larger and more consistent effect of the bedding experience. Female subjects which were raised on the less desirable of the two bedding substances (a commercial cellulose material, Sanicel) were found to "drift" away from their initial preference for the familiar bedding material. Experiment II investigates the effect on adult bedding preference of factorially varying preweaning and postweaning experience with each of the two bedding materials. The results of Experiment II again indicated substantial effects of experience on habitat preference as indicated by sleeping site and feeding site. Like those of Experiment I, the results again indicated that the habitat preference of males remains stable during preference testing regardless of which habitat is preferred, while that of females drifts away from the cellulose material in the course of preference testing. Even though males showed more stable habitat preference during the adult test period, they were also influenced by the postweaning experience, while females were found to be influenced by their early preweaning experience exclusively, regardless of varying postweaning experience. Experiments III and IV investigated whether the selection of birth site for the next generation is affected by prior bedding experience. Female mice were born and raised to adulthood on one of the two bedding substances, mated, and allowed to select the bedding material upon which they would raise their litters. The results indicated that, even though drift was present in sleeping and eating patterns of the cellulose-raised females, litter placement remained strongly dependent upon early bedding history. Experiment V was designed to determine the effect of several generations of experience with a given bedding material on bedding material preference, and to explore the possible genetic and non-genetic mechanisms for the mediation of such an effect. The results indicated that there was no change in habitat preference over generations and that the entire learning effect was complete following the first ,generation's initial exposure to the new habitat. Experiment VI investigated habitat preference and reproductive success of male offspring as a function of premating and mating bedding experience. The bedding-mating history of male offspring was found to have no effect on indices of reproductive success or habitat preference. The results of the study were discussed in terms of support given to the theory of sympatric speciation, the implications of the differential effect on bedding preference seen in male and female offspring, and the implications for evolutionary theory of the data indicating that the first generation offspring display maximal habitat conditioning.