Behavioural differences in non-reproductive adult females in a long-term selection experiment for litter size in mice

In a previous study, it has been shown that adult, non-reproductive female mice from a line selected for high litter size at birth (S-Line) have highe r residual feed intake (RFI) than females of a non-selected control line (C -line). Several studies have indicated that a higher RFI is related to a hi gher activity level. Differences in activity may suggest underlying differe nces in coping strategies. To investigate whether coping strategies have be en affected as a correlated effect of selection for high litter size, 48 no n-reproductive mature C- and S-Line females were twice subjected to an open field, seven times to a maze, once to a social confrontation and twice to a runway test. In the second open-field test, S-Line females crossed more s quares than C-line females and were less reserved to enter the centre of th e open field. In the maze tests, S-line females showed more locomotion acti vity than C-line females. They encountered dead-ends more often and returne d more often to the starting area in the first maze test. No differences we re found in their reaction rewards an extra-maze cue change. In the social confrontation test, S-line females showed more locomotion activity, were le ss immobile and investigated the floor and opponent less than C-line female s. S-line females ran faster in both runway tests than C-line females. Thes e results suggest that the novelty response of S-line females is more domin ated by an active coping style than that of C-Line females. However, more t ests, such as additional behavioural tests, physiological tests and neurobi ological tests are required to be more conclusive on whether selection for high litter size has resulted in mice that adopt the active coping strategy . (C) 2000 Elsevier Science B.V. All rights reserved.