Gender-selective patterns of aggressive behavior in Drosophila melanogaster

Abstract

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.

Fig. 1.

Schematic representations of average fights in mated (A) and virgin (B) female flies. The box sizes represent the numbers of transitions to and from the pattern, with the relative frequency given in percentages. Arrows between boxes represent the likelihood of transitions. Some transitions (red arrows) are unique to mated or virgin females. The large gray arrows outline two different behavioral loops. Note that fencing threat (blue box) and retreat (green box) are in opposite positions in the two schematics to prevent an overlap of transition arrows. The patterns are analyzed from first-order Markov chains (see Materials and Methods) by using 2,550 and 1,857 behavioral transitions from 26 mated and 26 virgin fights, respectively. HPF, high-posture fencing; WT, wing threat.

Fig. 2.

Female fighting pattern after simplification of analysis by removal of three categories of fencing (see text). The total number of transitions are 2,597 and the box and arrow dimensions are calculated as described for Fig. 1. The observed and expected transitions are given adjacent to each transition arrow. HPF, high-posture fencing; WT, wing threat.

Fig. 3.

An example of a fight between a pair of virgin females (A) and a pair of males (B). In the male fight, the subordinate fly retreated from the food cup without returning after the last encounter. In the female fight, both females were on the food cup for the 30-min period, and there were five reversals in the pattern of consecutive wins.

Fig. 4.

Behavioral patterns and transitions seen in fights between pairs of male and pairs of female D. melanogaster. Females and males share five common behavioral patterns (white boxes), whereas several gender-selective behavioral patterns also are seen (male, purple boxes; female, red boxes). The transition arrows and box sizes are as defined for Fig. 1, with the addition that the dashed line between hold and chase in males indicating a transition that approaches statistical likelihood. The large light blue arrows indicate similar transition loops, and the gray arrows indicate gender-selective transition loops. The female data are a rearrangement of the data presented in Fig. 2, and the male data were collected from 2,526 transitions from 376 encounters in 19 trials.