Attraction of male golden hamsters (Mesocricetus auratus) to the odors of male conspecifics

Social-defeat stress suppresses scent-marking and social-approach behaviors in male Mongolian gerbils (Meriones unguiculatus)

In many species, social-defeat stress induces behavioral changes in subordinate individuals. The present study examined how social-defeat stress affected scent-marking and approach behaviors in male Mongolian gerbils and whether socially defeated males selectively avoided dominant males. In Experiment 1, each of 11 gerbils was defeated by a dominant gerbil during a short social confrontation (10 min in total). For Experiment 2, the same animals were used two weeks after the end of Experiment 1. Each subject was again similarly defeated, but the two gerbils were then kept in the same cage, separated by a wire mesh for 24 h. Behavioral changes in socially defeated males were observed after social defeat; both experiments were replicated three times. After acute social defeat in Experiment 1, male gerbils did not change their scent-marking activity and frequently approached the dominant males. In contrast, males decreased scent-marking activity and approach behavior toward dominant males in Experiment 2. The amount of time defeated males approached unfamiliar males was also reduced, suggesting that social-defeat stress reduces scent-marking motivation and conspecific approach behavior rather than inducing social avoidance toward a specific individual. These findings showed that the severity of social-defeat stress is an important factor in subsequent behavioral changes in male Mongolian gerbils.

Recognition of competitors by male golden hamsters

Golden hamsters, like many animals, form dominant/subordinate relationships after aggressive encounters. We examined whether behavioral responses by males that won or lost fights would differ toward familiar and unfamiliar male stimulus animals. In Experiment 1, male winners or losers of fights explored an arena containing a confined stimulus animal that was either familiar or novel and had either won or lost a fight. Compared to dominant males, losers spent less time in proximity to stimulus males and investigated them less. Losers also displayed higher levels of stretch-attend postures (indicative of risk assessment) than winners, and they showed more escape and locomotion in response to familiar winners than to unfamiliar winners, indicating recognition of the male that they had lost to. In Experiment 2, losers scent marked less to the odors of a familiar winner than to those of an unfamiliar winner. Thus, male hamsters appear to use familiarity with a former opponent's odors to adaptively regulate their responses to variations in social threat.

Differential effects of prior dominance or subordination experience on conspecific odor preferences in mice

Preferences for the soiled bedding odors of familiar and unfamiliar conspecifics were assessed among male mice rendered dominant or subordinate by a series of resident-intruder encounters. Alpha males preferred the odors of their familiar antagonist most strongly. Subordinates, in contrast, showed strongest preferences for unfamiliar females and a weaker preference for alpha odors. When female odors were eliminated from the preference test, alphas continued to show the strongest preference for familiar subordinate odors while subordinates displayed roughly equivalent preference for the odors of familiar alphas and unfamiliar males. It is suggested that the apparent mild preferences of subordinates for dominant conspecific odors reflects fear motivated risk assessment. In contrast, approaches of dominants to subordinate odors seems to be appetitively motivated. Generally recognizable subordination odors may be useful to unfamiliar males in recognizing exploitable resources.