NESTING AND FITNESS - LIFETIME REPRODUCTIVE SUCCESS IN-HOUSE MICE BIDIRECTIONALLY SELECTED FOR THERMOREGULATORY NEST-BUILDING BEHAVIOR

To test the hypothesis that large, well-built, nests are an important component of fitness, we kept 12 mating pairs of two high-selected, tw o control, and two low-selected lines, selected for thermoregulatory n est-building behavior, at 22 and 4 degrees C with access to 10 g of co tton to build a nest, for a period of 180 days. Measurements included number of lifters born per family, number of young per litter born and surviving up to 40 days of age, nest type built by the parents, and w eight gain of the young from weaning (20 days of age) to 40 days of ag e. In all lines the production and survival of offspring was substanti ally decreased at 4 degrees C compared to 22 degrees C, but the high-s elected lines produced more and better-quality offspring, surviving up to 40 days of age at both temperatures compared to the control and lo w-selected lines. This indicates that thermoregulatory nest-building b ehavior and evolutionary fitness are closely associated.