Male and female aggression at different reproductive stages was investigated in
pairs of wild mice. Fourteen pairs of laboratory-outbred wild mice were
established, each pair living in a multiple set of cages, connected by runaways.
Intruder tests were carried out at different stages of the reproductive cycle,
i.e. 48 h after introduction, during pregnancy and lactation. In these stages, a
female, a male and two pups were consecutively introduced in each territory (24
h separating each intrusion). Male residents were highly aggressive towards (and
always intolerant of) male but not female intruders. Conversely, resident
females preferentially attacked same sex intruders after colony establishment
and during pregnancy, but they attacked either sex of intruder when nursing
young. Seven out of 14 female intruders were tolerated 48 h after introduction
of residents but tolerance of females decreased during pregnancy and lactation.
Male and female residents were essentially responsible for the intolerance of
same-sex intruders. Both males and females exhibited infanticide, but sex
differences in the timing of attack on alien pups were observed. In the 7
colonies where the intruder female was tolerated (since that two females were
present) only one female reproduced successfully. This suggests that, as in
males, females of this stock compete for the opportunity to reproduce; they can
be exclusively territorial or form a dominance hierarchy which probably
determines reproductive success. While male competitive aggression appears to be
mostly directed to other males, females seem largely responsible of the
regulation of the reproductive potential of a deme unit throughout intrasexual
aggression (intolerance towards other females), and possibly also inhibition of
subordinate reproduction and killing of unrelated pups.
Social Stress Increases Anxiety-Like Behavior Equally in Male and Female Zebrafish
