In male house mice, differences have been reported in behavioural strategies to cope with challenges. These differences are related to a differentiation in territorial aggression. In the present study it was investigated whether consistent differences exist in response to challenges among female mice. For this purpose, females from lines selected for male s hort and l ong a ttack l atency in a resident-intruder paradigm were used. SAL females were significantly and consistently more prone to engage a non-social challenge than LAL females, both during development as in adulthood. This was measured in an unfamiliar object test and an open field test. To assess the response of females to social challenges, SAL and LAL dams were confronted with an intruder at regular intervals during the lactation period. SAL as well as LAL dams showed very short attack latencies and there were no differences between SAL and LAL mice. It is suggested that the pup protection function of maternal aggression does not allow the development of significant variation in maternal aggression. This infers that maternal aggression is not a suited parameter to assess the response of female mice to a social challenge.
House mice of selection lines for short attack latency (SAL) and long attack latency (LAL) differ fundamentally in the way they interact with their environment. A previous study showed marked differences in maternal behaviour between dams from both lines. The present study was designed to determine, by reciprocal cross-fostering, to what extent the postnatal SAL and LAL maternal environment contributes to observed differences in aggression and behavioural strategy between SAL and LAL mice. At a subadult age there were neither differences in attack latency between lines nor between control and cross-fostered groups. In adulthood there was a significant difference in attack latency between SAL and LAL mice, which was not influenced by maternal type. Also coping, as measured by the readiness to encounter a challenge, was not influenced by maternal type. Both at a subadult age as in adulthood, SAL mice encountered unknown situations much faster than LAL mice, but there were no differences between control and cross-fostered groups. As found in previous studies, SAL mice were more routine-like in their behaviour than LAL mice. However, SAL mice that were reared by LAL dams were more flexible in their behaviour than SAL mice reared by their own mothers. This postnatal maternal effect on
To investigate the relationship between aggression and routine-like behaviour the response of male mice of bidirectionally selected lines for attack latency to a change in the social and non-social environment has been measured. In a non-social situation the extent of routine-like behaviour was measured in a Y-maze in which only one of the two arms gave access to the food compartments. The number of errors made in response to reversal of the arm that was blocked was taken as indicator for the degree of routine formation. Males of the short attack latency (SAL) line made significantly more errors, and hence were more routine-like in their performance, than mice of the long attack latency (LAL) line. Males of the LAL line that nevertheless had short attack latencies (i. e. aggressive LAL mice) turned out to be flexible in their behaviour; their response was similar to that of the non-aggressive LAL males. In a social situation SAL and aggressive LAL mice were used to investigate routine formation in attacking behaviour. The males were given different amounts of experience with male opponents after which their own female was introduced as opponent. The more extended the experience with male intruders was, the more SAL males subsequently attacked their female. In contrast, LAL mice appropriately changed their behaviour towards the female opponent. Thus, the attacking behaviour of SAL mice gets routine-like, whereas that of LAL males remains flexible. It is concluded that selection for attack latency generally coincides with selection for routine-like behaviour, suggesting that these two factors are influenced by many of the same genes. Regarding the fact that aggressive males of the LAL line show flexible behaviour, it may be proposed that with the phenotypic selection for attack latency there has in fact been selected for a mechanism that determines the organization (routine-like vs flexible) of behaviour.