PubMed · 14816486
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E FREDERICSON. 1951. Time and aggression.. https://doi.org/10.1037/h0059108
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In the laboratory environment, rodents are usually housed in unisexual groups, which are assembled after weaning. Housing of unfamiliar subjects has been described, however, as a stressful social setting for rodents and other mammals. Aim of the present study was to evaluate whether the age at which house mice are grouped might affect their behavior and physiology. Male or female unisexual groups were formed at different ages: at weaning, i.e., before puberty (JUV); at adolescence, i.e., after puberty (AD); and controls were raised with siblings since birth (CON). Results show that age at group formation induced several behavioral and physiological alterations in males but not in females. Specifically, when compared to controls, JUV males showed higher aggression, smaller preputial gland, and a marked reduction of neophobia in the free exploratory paradigm. Fewer changes occurred in the AD males, which showed reduced neophobia in the free exploratory paradigm and, when adults, a reduction in body weight. Females were not affected by the experimental treatment. Surprisingly, the basal corticosterone assessed at the nadir was lower for both males and females JUV and AD respect to CON. In conclusion, it is clear that mixing groups at different ages has profound effects on mouse behavior and physiology.
The question of why territorial residents usually win asymmetrical owner-intruder contests is critical to our understanding of animal contest evolution. Game theory suggests that, under certain conditions, residency could be used as an arbitrary means of contest settlement in a manner analogous to tossing a coin. Key empirical support for this idea is provided by a study on the speckled wood butterfly (Pararge aegeria); however, this result has proven controversial. We show conclusively that residency does not serve as an arbitrary cue for contest settlement in this species. By means of a series of manipulative experiments, conducted on two phenotypically divergent populations of P. aegeria, we also rule out the recently presented alternative that contests are settled due to resource-correlated asymmetries in thoracic temperature. Our results instead suggest that more intrinsically aggressive males accumulate as residents and continue to win due to the self-reinforcing effect of prior winning experience. Truly arbitrary contest settlement may be rare or non-existent in the wild.
Complex behaviors, such as aggression, are comprised of distinct stereospecific behavioral patterns (modules). How such patterns get wired into nervous systems remains unknown. Recently, we reported on a quantitative analysis of fighting behavior in male flies of the common Canton-S strain of Drosophila melanogaster. Here, we report a similar analysis of fighting behavior in females of the same species. Fights were carried out between pairs of virgin and pairs of mated females in competition for a yeast resource. Each fight was videotaped and analyzed by using transition matrices and Markov chain analyses. We observe only small difference in fighting intensity between virgin and mated females. In contrast to what is seen in male fights, however, no clear hierarchical relationship is formed in the female fights. A further comparison of the behavioral patterns making up male and female fights reveals that some modules are shared by both sexes, whereas others are highly selective. Within the shared components, transitions between the modules also show gender-selective differences. By using the powerful genetic methods available for examining behavior in fruit flies, it should be possible to use the gender-selective differences in fighting behavior to address the question of how these behavioral patterns get established in the brains of fruit flies.