The closed environment of the fig receptacle and its influence on male conflict in the old World fig wasp, Philotrypesis pilosa

Abstract

The influence of the environment on the fighting behaviour and susceptibility to injury of male Phylotrypesis pilosa, a parasitic fig wasp, was examined with reference to a recent model of contest competition. The model was extended by deriving an expression for the overall rate at which contest costs accumulate during resource exploitation. Predictions were then made about the cost and frequency of fights, and about the overall cost of fighting with regard to variations both in the density of males and females and in the ratio of females to male competitors. The cost of fighting was estimated from the length and frequency of fights and by the extent of male injuries. The overall cost of conflict was highest at an intermediate density of males, as predicted. The overall cost also rose as the density of females increased but, unexpectedly, did not peak at an intermediate female density. A predicted relationship between fighting cost and the ratio of female number to male competitor number was also missing. These discrepancies were associated with a difference in the actual and assumed form of sperm utilization that followed mating, and with the surprising ability of males to alternate rapidly between guarding and exploratory behaviours. The data give no indication that males are either reducing their levels of aggression in fights with relatives, or increasing them to establish dominance when encountering the same competitor repeatedly.