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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2004.09.014 Byline: P. Palanza, D. Della Seta, P.F. Ferrari, S. Parmigiani Abstract: We assessed the effects of different situational or social determinants on the regulation of female-female competition. We carried out a laboratory study to examine aggression and reproductive success of pairs of wild female mice, Mus musculus domesticus spp., as a function of the timing of settlement of females relative to that of males and the genetic relatedness and familiarity between females (sibling versus nonsibling females). After a few days of cohabitation with a male, females were highly aggressive towards, and intolerant of, any intruder female, regardless of relatedness and familiarity. In this condition, monogamy was the resulting mating pattern in approximately 80% of cases. Conversely, pairs of females who made contact with each other at the same time, or prior to cohabitation with a male, showed comparatively little aggression and a high degree of reciprocal tolerance. Only in these latter conditions did genetic relatedness and familiarity between females influence their behavioural interactions and reproductive success. Although nonsibling pairs showed higher frequencies of aggressive interactions than siblings, polygyny resulted in 97% of cases. However, in most sibling groups both the females weaned young and had greater reproductive success than nonsiblings. Nonsibling females appeared to compete for reproduction through the inhibition of reproduction or infanticide. These findings suggest that the timing of male/female settlement in a deme determines the level of female competition, which, in turn, affects the resulting mating pattern. Only when females showed social tolerance did genetic relatedness and familiarity influence reproductive success. Author Affiliation: (*) Dipartimento di Biologia Evolutiva e Funzionale, Universita degli Studi di Parma, Italy (a ) Dipartimento di Fisiologia, Universita degli Studi di Siena, Italy Article History: Received 6 February 2003; Revised 30 April 2003; Accepted 5 September 2004 Article Note: (miscellaneous) MS. number: 7614R

Cross fostering is a widely used laboratory practice. However, relatively few studies have directly investigated the carry-over effects of this procedure in adult animals. The aim of the present study is to investigate the late effects of cross fostering (CF) at birth (in litters composed of no siblings) on adult mice. When adults, cross-fostered male and female mice were examined for intrasex aggression, and levels of emotionality, exploration and anxiety. In addition, body weight was monitored, several internal organs were weighed and plasma corticosterone levels were measured. When compared to controls, body weight of CF male and female mice was increased, at least after early puberty. CF males showed smaller preputial glands, while basal corticosterone level was not affected by cross fostering. In the free-exploratory test, CF males, but not females, showed a behavioral profile suggestive of lower anxiety. These effects in adulthood cannot be ascribed to differences in the maternal care received, which was not affected by cross fostering. In conclusion, cross fostering at birth induced a number of behavioral and physiological alterations in mice, particularly in males. These findings should be carefully evaluated when applying cross fostering procedure to laboratory animals. [ABSTRACT FROM AUTHOR]

Swiss CD-1 lactating mice show a different pattern of attack toward intruders of differing sex, displaying defensive attack against the male (bites on the head and ventrum associated with fear) and offensive attack against the female (bites on the back and flanks with no elicitation of fear). This dichotomy may reflect diverse functions of maternal aggression: the attack toward males (the more infanticidal gender in laboratory strains) has been interpreted as a counterstrategy to infanticide, whereas the attack toward females may serve to establish a social hierarchy or to space rivals of the same sex. In terms of proximal mechanisms, fear may be a key factor involved in the modulation of the different patterns of attack. In Experiment 1 we compared the pattern of attack of lactating females in Swiss CD-1 and Wild mice toward male and female intruders in relation to fear components of behavior of the attacking dams. Results showed that in Swiss mice, male intruders were attacked with a defensive type of attack accompanied by high levels of fear, whereas female intruders did not elicit fear in the attacking animal but were attacked with an offensive pattern. In Wild mice, both types of intruders were attacked with a defensive pattern; notwithstanding, fear was evident only toward male intruders. This suggests that fear is not totally responsible for the expression of the defensive type of attack. To test the hypothesis that defensive attack toward male and female intruders may be related to the infanticidal potential of the intruder, Experiment 2 examined levels of infanticide in both male and female Swiss CD-1 and Wild mice. Swiss female mice showed virtually no infanticidal behavior, whereas Swiss males and both sexes of Wild mice showed similarly high levels of infanticide (55%–75%). From a game theory perspective, the defensive pattern of maternal attack toward female intruders in Wild mice is discussed as “extreme” defense of a high value resource and thus, functionally, a competitive form of aggression. Aggr. Behav. 26:193–203, 2000. © 2000 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Lactating mice respond differently to male and female conspecific intruders, displaying defensive attack towards the former and offensive attack towards the latter. Two studies are reported in which the effects of naloxone on this differential response pattern were assessed. In the first study, lactating residents were pretreated with saline or naloxone (0.5, 2.5 mg/kg) and consecutively confronted with intruders of differing sex. Results suggested that attack (offensive) against female conspecific is more sensitive to the inhibitory effects of opiate-receptor blockade than attack (defensive) on males. This conclusion was strengthened in a follow-up study, in which independent groups of lactating residents were used to further examine the effects of naloxone (0.5 mg/kg) on response to male and female intrusion. Analysis indicated that this low dose of naloxone significantly inhibited attack on female, but not on male, intruders. Indeed, in response to male, but not to female, intrusion, naloxone-treated residents showed a significant increase in fear-related behaviour. Findings are discussed in relation to the motivational differences in the response of lactating mice to intruders of differing sex and to possible mechanisms underlying the reported differential effects of opiate-receptor blockade. [ABSTRACT FROM AUTHOR]