Fear-related behaviour in two mouse strains differing in litter size

The present experiment compared the fear-related behaviour of a mouse strai n selected over 101 generations for high litter size with that of a randoml y selected strain. The H-strain, selected for large litter size, has a mean (+/- SD) litter size at birth of 21.5 +/- 3.5 pups. The randomly bred C-st rain has a mean (+/- SD) litter size of 9.6 +/- 2.2 pups. The elevated plus -maze, the light:dark test and a resident:intruder test were used to measur e how the mice responded to novelty. In the elevated plus-maze, a well-vali dated model of animal anxiety, the H-strain was significantly more anxious (having a lower percentage of entries into open arms) than the C-strain at 9 weeks of age. In the light:dark test, in which the light levels were simi lar to those in the home environment, the H-strain did not differ significa ntly from the C-strain in its avoidance of the brightest area. In the resid ent:intruder test where aggression-trained, older H-strain males were the r esidents, 11-week-old intruding mice of the C-strain spent a higher percent age of their time in flight and immobility than intruders of the H-strain. There were clear anxiety- and fear-related differences between the strains, which may be related to their selection history. The results illustrate a need for further studies on the consequences of selection for increased pro duction for the ability of animals to adapt to their home environment and c ope with environmental changes.