Extensive Reorganization of Behavior Accompanies Ontogeny of Aggression in Male Flesh Flies

Darrell Moore,Edith Seier,Karl H Joplin,Caleb Paquette,J Dylan Shropshire,Mark A Frye

doi:10.1371/journal.pone.0093196

Abstract

Aggression, costly in both time and energy, is often expressed by male animals in defense of valuable resources such as food or potential mates. Here we present a new insect model system for the study of aggression, the male flesh fly Sarcophaga crassipalpis, and ask whether there is an ontogeny of aggression that coincides with reproductive maturity. After establishing that reproductive maturity occurs by day 3 of age (post-eclosion), we examined the behavior of socially isolated males from different age cohorts (days 1, 2, 3, 4, and 6) upon introduction, in a test arena, with another male of the same age. The results show a pronounced development of aggression with age. The change from relative indifference to heightened aggression involves a profound increase in the frequency of high-intensity aggressive behaviors between days 1 and 3. Also noteworthy is an abrupt increase in the number of statistically significant transitions involving these full-contact agonistic behaviors on day 2. This elevated activity is trimmed back somewhat by day 3 and appears to maintain a stable plateau thereafter. No convincing evidence was found for escalation of aggression nor the establishment of a dominance relationship over the duration of the encounters. Despite the fact that aggressive interactions are brief, lasting only a few seconds, a major reorganization in the relative proportions of four major non-aggressive behaviors (accounting for at least 96% of the total observation time for each age cohort) accompanies the switch from low to high aggression. A series of control experiments, with single flies in the test arenas, indicates that these changes occur in the absence of the performance of aggressive behaviors. This parallel ontogeny of aggressive and non-aggressive behaviors has implications for understanding how the entire behavioral repertoire may be organized and reorganized to accommodate the needs of the organism.

Highlights

Aggression is widespread throughout the animal kingdom [1]
Flesh Flies Fight A raster plot (Fig. 3) showing one minute of activity for one representative opponent pair taken from three different age cohorts illustrates some general characteristics of the various behaviors performed by male flesh flies in the experimental arena
We introduce the flesh fly S. crassipalpis as a model system for exploring fundamental questions concerning how the nervous system may organize a variety of behaviors, including aggressive acts, and how these patterns may change with age

Summary

Introduction

Aggression is widespread throughout the animal kingdom [1]. Typically, male animals will defend valuable resources in the environment such as food, shelter, and access to mates. Cost-benefit studies of territoriality have been carried out on a wide variety of vertebrates, including lizards [4], salamanders [5], Siamese fighting fish [6], Golden-winged Sunbirds [7], rufous hummingbirds [8], and golden lion tamarins [9]. Such studies have been performed on invertebrates, including aphids [10], crayfish [11], crab spiders [12], fruit flies [13], and a variety of aquatic insects [14]

Methods

Results

Conclusion