Dominant-subordinate relationships in hamsters: sex differences in reactions to familiar opponents

Abstract

In the majority of mammalian species, males are dominant over and more aggressive than females. In contrast, some reports suggest that female golden hamsters are more aggressive than males but systematic comparisons using the same methods for both sexes are rare. We observed same-sexed pairs of hamsters over repeated trials to assess whether sex differences existed in the level of agonistic behavior and in the development and maintenance of dominant-subordinate relationships with familiar partners. There were no sex differences in measures of agonistic behavior or fear responses (fleeing) during the initial series of three trials on the first day of testing. Following a four-day interval, males that had lost in session 1 showed fearful responses to a familiar dominant male and were not likely to engage in a fight with him. In contrast, females that lost the initial fights were not fearful and fought vigorously with the familiar winner in subsequent encounters. Although the amount of agonistic behavior engaged in by females did decrease over the course of the three sessions, females that lost did not demonstrate an increase in fear, as measured by the latency to flee. Males that lost fights did show increased fear during later trials and sessions. These results suggest that female hamsters are less affected by losing fights than males are and thus that females are less likely than males to develop highly polarized dominant-subordinate relationships. Further work is needed to understand the mechanisms underlying these sex differences.

Figure 1

Schematic representation of the experimental design. Subjects were tested in three different sessions 4 days apart so that females would always be tested on the same day of their estrous sycle. In each session, subjects had three aggressive encounters with a four-minute inter-trial interval

Figure 2

Session 1: Histograms depicting the mean (+/− SEM) scores of males (n=13 pairs) (grey) and females (n=15 pairs) (white) for (A) probability of fighting, (B) the latency to fight, (C) number of fights (D) time spent fighting, (E) the probability of fleeing, and (F) latency to flee.

Figure 3

Session 2: Histograms depicting the mean (+/− SEM) scores of males (n=13 pairs) (grey) and females (n=15 pairs) (white) for (A) probability of fighting, (B) the latency to fight, (C) number of fights (D) time spent fighting, (E) the probability of fleeing, and (F) latency to flee.

Figure 4

Session 3: Histograms depicting the mean (+/− SEM) scores of males (n=13 pairs) (grey) and females (n=15 pairs) (white) for (A) probability of fighting, (B) the latency to fight, (C) number of fights (D) time spent fighting, (E) the probability of fleeing, and (F) latency to flee.